Complete List of Komatsu Error Codes: Meanings, Causes, and Troubleshooting Solution
Komatsu error codes are designed to help operators and mechanics identify abnormal conditions in the engine, electrical, hydraulic, fuel, and machine-control systems.
When the machine controller detects an abnormal sensor signal, voltage, pressure, temperature, or communication condition, an error code may appear on the monitor.
However, the appearance of an error code does not always mean that the component mentioned in the code is damaged and must be replaced immediately.
For example, a rail-pressure sensor error may be caused by:
A loose connector.
Broken wiring.
A short circuit.
Poor grounding.
Incorrect sensor supply voltage.
A clogged fuel filter.
Air entering the fuel system.
Actual fuel-pressure problems.
For this reason, an error code should be treated as an initial diagnostic clue, not as the final conclusion.
This article explains common Komatsu error codes, their meanings, possible causes, symptoms, and recommended troubleshooting procedures.
The information is particularly useful for Komatsu excavators such as the PC200, PC210, PC220, PC300, PC350, and PC400, as well as other Komatsu machines equipped with electronic common-rail engines.
Important notice: Error-code meanings, connector locations, standard values, and troubleshooting procedures may differ depending on the machine model, serial number, engine type, emissions specification, and controller version. Always confirm the code using the correct Komatsu Operation and Maintenance Manual or Shop Manual.
What Is a Komatsu Error Code?
A Komatsu error code is a combination of letters and numbers used by the machine controller to indicate an abnormal condition.
Several code formats may appear on Komatsu machines.
| Code format | Example | System commonly involved |
|---|---|---|
| CA | CA111, CA559, CA2249 | Engine and common-rail system |
| AA | AA10NX | Air-intake warning |
| AB | AB00KE | Charging and electrical system |
| B@ | B@BCNS, B@HANS | Temperature, oil level, and pressure |
| 879 | 879AKA | Air-conditioning system |
| 989 | 989L00 | Controller lock or communication |
The same code format may not have exactly the same diagnostic procedure on every machine.
A PC200-8, PC200-10, PC300-8, PC400-11, D375 dozer, HD785 dump truck, and WA600 wheel loader may use different controllers, sensors, wiring diagrams, and standard values.
Common Komatsu Engine Error Codes
1. CA111 – ECM Critical Internal Failure
Meaning
CA111 generally indicates a critical internal failure in the Engine Control Module, commonly called the ECM or engine controller.
On some Komatsu models, this fault may be related to internal memory, internal power-supply circuitry, or controller processing failure.
Possible symptoms
The engine is difficult to start.
The engine does not start.
The engine stops unexpectedly.
Engine speed becomes unstable.
Throttle response becomes abnormal.
The engine enters derate mode.
Several fault codes appear at the same time.
Communication with the engine controller is interrupted.
Possible causes
Battery voltage is too low.
Battery voltage is unstable.
Battery terminals are loose or corroded.
Engine-controller ground is poor.
ECM power-supply wire is open.
ECM power-supply wire is shorted.
Fuse or relay failure.
Water or corrosion inside the ECM connector.
Alternator output is unstable.
Internal ECM failure.
Troubleshooting procedure
Measure battery voltage with the starting switch OFF.
Measure battery voltage with the starting switch ON.
Check voltage during engine cranking.
Inspect positive and negative battery terminals.
Inspect engine, chassis, and controller ground connections.
Check ECM fuses and relays.
Inspect the ECM power-supply circuit.
Turn the starting switch OFF before disconnecting the ECM connector.
Check for water, corrosion, loose pins, or pushed-back terminals.
Inspect related battery-voltage and sensor-supply codes.
Confirm wiring continuity between the fuse, relay, and ECM.
Inspect the ECM only after all external circuits have been confirmed normal.
Do not replace the ECM before checking the battery, charging system, ground connections, fuses, relays, and wiring.
2. CA115 – Engine Speed and Backup Speed Sensor Error
Meaning
CA115 indicates an abnormal signal from the engine-speed sensor and backup-speed sensor on certain Komatsu machines.
These sensors allow the engine controller to determine engine speed, crankshaft position, and injection timing.
Possible symptoms
The engine cranks but does not start.
The engine is difficult to start.
Engine speed is not displayed correctly.
Engine speed becomes unstable.
Engine power decreases.
The engine stops suddenly.
The engine enters derate mode.
Possible causes
Crankshaft speed sensor failure.
Camshaft or backup-speed sensor failure.
Loose sensor connector.
Broken sensor wiring.
Wiring shorted to ground.
Wiring shorted to power.
Metal particles attached to the sensor tip.
Incorrect sensor installation.
Incorrect sensor air gap.
Damaged or loose sensing ring.
Incorrect sensor supply voltage.
Troubleshooting procedure
Check whether the engine cranks normally.
Monitor engine speed during cranking.
Inspect the crankshaft sensor connector.
Inspect the camshaft sensor connector.
Clean metal particles from the sensor tip.
Inspect the sensor harness for damage.
Check wiring continuity between the sensor and ECM.
Measure sensor resistance or output according to the shop manual.
Inspect sensing-ring condition.
Check sensor mounting and air gap.
Replace the sensor only if the measured value is outside specification.
3. CA122 – Charge-Air Pressure Sensor High Error
Meaning
CA122 indicates that charge-air or boost-pressure sensor signal voltage is too high.
The word “high” usually refers to high electrical signal voltage. It does not automatically mean that actual turbocharger pressure is too high.
Possible causes
Signal wire shorted to positive voltage.
Sensor ground circuit open.
Loose connector terminal.
Corroded connector.
Boost-pressure sensor failure.
Reference voltage too high.
ECM sensor circuit failure.
Troubleshooting procedure
Inspect the charge-air pressure sensor connector.
Check for corrosion or loose terminals.
Check sensor reference voltage.
Check sensor ground.
Check the signal wire for short to positive voltage.
Compare boost-pressure data with atmospheric pressure while the engine is stopped.
Check whether the monitor value is realistic.
Repair the wiring if a short circuit is found.
Replace the sensor only if the wiring and voltage are normal.
4. CA123 – Charge-Air Pressure Sensor Low Error
Meaning
CA123 indicates that charge-air pressure sensor signal voltage is too low.
Possible causes
Signal wire shorted to ground.
Sensor power-supply circuit open.
Sensor connector disconnected.
Poor connector contact.
Boost-pressure sensor failure.
Reference-voltage circuit problem.
ECM circuit problem.
Troubleshooting procedure
Inspect the sensor connector.
Check the connector terminals.
Measure reference voltage.
Check the sensor ground.
Check signal-wire continuity.
Check for a short circuit to ground.
Compare the monitor reading with actual machine conditions.
Repair wiring faults before replacing the sensor.
CA123 is different from actual low boost pressure caused by:
A clogged air filter.
A leaking intake hose.
A leaking charge-air cooler.
Turbocharger wear.
Exhaust restriction.
CA123 mainly indicates an electrical sensor-circuit problem.
5. CA131 – Throttle Sensor High Error
Meaning
CA131 indicates that fuel-control dial or throttle-sensor circuit voltage is too high.
Possible symptoms
Engine speed does not follow the control dial.
Engine speed remains at one value.
Engine speed increases unexpectedly.
Throttle response is unstable.
Engine derate occurs.
Possible causes
Fuel-control dial failure.
Signal wire shorted to positive voltage.
Throttle-sensor ground open.
Loose connector.
Corroded connector.
Reference voltage too high.
Engine-controller failure.
Troubleshooting procedure
Rotate the fuel-control dial from minimum to maximum.
Monitor throttle percentage.
Check whether the value changes smoothly.
Inspect the connector behind the fuel-control dial.
Measure reference voltage.
Check sensor ground.
Measure signal voltage.
Check the signal wire for short to power.
Replace the fuel-control dial if the output is unstable or does not change.
6. CA132 – Throttle Sensor Low Error
Meaning
CA132 indicates that fuel-control dial signal voltage is too low.
Possible causes
Signal wire shorted to ground.
Sensor power supply open.
Connector disconnected.
Fuel-control dial failure.
Poor ground.
ECM circuit problem.
Troubleshooting procedure
Inspect the fuel-control dial connector.
Check the power supply.
Check the fuse.
Check sensor ground.
Measure signal voltage.
Check wiring continuity to the ECM.
Check for short circuit to ground.
Replace the fuel-control dial only after confirming that the wiring is normal.
7. CA144 – Coolant Temperature Sensor High Error
Meaning
CA144 indicates that coolant-temperature sensor signal voltage is too high.
This code does not automatically mean that the engine coolant is overheating.
Possible causes
Sensor connector disconnected.
Signal wire open.
Sensor ground open.
Connector corrosion.
Coolant-temperature sensor failure.
ECM circuit failure.
Troubleshooting procedure
Check coolant level when the engine is cold.
Inspect the coolant-temperature sensor connector.
Check the signal wire.
Check sensor ground.
Compare monitor temperature with actual temperature.
Measure sensor resistance.
Compare resistance with the shop-manual specification.
Replace the sensor if its resistance is outside specification.
8. CA145 – Coolant Temperature Sensor Low Error
Meaning
CA145 indicates that coolant-temperature sensor signal voltage is too low.
Possible causes
Signal wire shorted to ground.
Sensor internally shorted.
Water inside the connector.
Damaged wiring harness.
Poor connector condition.
ECM circuit problem.
Troubleshooting procedure
Inspect the sensor connector.
Remove water and corrosion.
Check the signal wire for short to ground.
Measure sensor resistance.
Compare monitor temperature with actual engine temperature.
Inspect the wiring harness near hot or vibrating components.
If the monitor shows a very high coolant temperature while the engine is still cold, the sensor circuit may be shorted.
9. CA153 and CA154 – Charge-Air Temperature Sensor Error
| Code | Meaning |
|---|---|
| CA153 | Charge-air temperature sensor signal high |
| CA154 | Charge-air temperature sensor signal low |
These codes relate to the intake-air temperature sensor after the turbocharger or charge-air cooler.
Possible causes
Loose sensor connector.
Signal wire shorted.
Signal wire open.
Poor sensor ground.
Incorrect reference voltage.
Temperature sensor failure.
Damaged harness caused by heat.
Troubleshooting procedure
Inspect the temperature-sensor connector.
Measure reference voltage.
Check sensor ground.
Check signal-wire continuity.
Compare intake temperature with ambient temperature when the engine is cold.
Inspect wiring near the turbocharger and exhaust system.
Replace the sensor if wiring and voltage are normal.
10. CA155 and CA488 – Charge-Air Temperature Too High
Meaning
These codes indicate that charge-air temperature is too high on certain Komatsu models.
The engine controller may reduce engine speed or torque to protect the engine.
Possible causes
Charge-air cooler clogged with dust.
Radiator clogged.
Cooling fan speed too low.
Fan-drive problem.
Intake hose bent or restricted.
Hot air recirculating around the radiator.
Excessive engine load.
High ambient temperature.
Temperature sensor reading incorrectly.
Troubleshooting procedure
Clean the radiator.
Clean the charge-air cooler.
Check fan speed.
Inspect fan drive and fan-control system.
Inspect radiator sealing.
Inspect turbocharger hoses.
Inspect intercooler hoses.
Compare actual temperature with monitoring data.
Reduce machine load if temperature continues to increase.
Komatsu IMV and Fuel-Control Error Codes
11. CA271 – IMV or PCV Short Circuit
Meaning
CA271 generally indicates a short circuit in the Inlet Metering Valve or Pressure Control Valve circuit.
The IMV controls the amount of fuel entering the high-pressure supply pump.
Possible causes
IMV coil shorted.
Wiring shorted to ground.
Wiring shorted to power.
Connector damaged.
Harness rubbing against the engine.
ECM driver-circuit failure.
Troubleshooting procedure
Turn the starting switch OFF.
Inspect the IMV connector.
Inspect the harness between the IMV and ECM.
Measure IMV coil resistance.
Check for short to ground.
Check for short to power.
Inspect fuel-system contamination.
Test the IMV using the correct diagnostic procedure.
12. CA272 – IMV or PCV Open Circuit
Meaning
CA272 indicates an open circuit in the IMV or PCV control circuit.
Possible causes
IMV coil open.
Connector disconnected.
Broken wire.
Loose connector terminal.
Corrosion.
ECM control-circuit failure.
Troubleshooting procedure
Inspect the IMV connector.
Check wiring continuity.
Measure IMV coil resistance.
Inspect connector terminals.
Repair broken wiring.
Replace the IMV only if the coil is confirmed open.
Inspect the ECM only after external circuits are confirmed normal.
Komatsu Injector Error Codes
On certain six-cylinder Komatsu engines, injector codes may appear in the following sequence.
| Code | Meaning |
|---|---|
| CA322 | Injector No. 1 open or short circuit |
| CA323 | Injector No. 5 open or short circuit |
| CA324 | Injector No. 3 open or short circuit |
| CA325 | Injector No. 6 open or short circuit |
| CA331 | Injector No. 2 open or short circuit |
| CA332 | Injector No. 4 open or short circuit |
| CA351 | Injector drive-circuit error |
The injector-number sequence may be different on other engines.
Possible symptoms
Engine misfire.
Rough idle.
Low engine power.
Excessive smoke.
Difficult starting.
Engine vibration.
Cylinder contribution imbalance.
Engine derate.
Possible causes
Loose injector connector.
Broken injector wiring.
Wiring shorted to ground.
Wiring shorted to power.
Connector terminal pushed backward.
Injector solenoid failure.
Incorrect injector calibration code.
ECM injector-driver failure.
Troubleshooting procedure
Turn the starting switch OFF before disconnecting injector connectors.
Inspect the injector harness.
Inspect each injector connector.
Check wiring exposed to heat, oil, or vibration.
Measure injector resistance according to the manual.
Check wiring continuity from the injector to the ECM.
Check for short to ground or power.
Perform a cylinder cut-out test if supported.
Confirm that the injector calibration code is correct.
Do not replace the ECM before checking the injector and wiring.
13. CA342 – Calibration Code Incompatibility
Meaning
CA342 indicates that calibration data in the engine controller does not match the injector or engine configuration.
Possible causes
Incorrect injector calibration code entered.
Injector replaced without registering the new code.
Injector codes entered for the wrong cylinders.
ECM replaced.
ECM reprogrammed incorrectly.
Controller data corrupted.
Controller configuration does not match the engine.
Troubleshooting procedure
Record the code printed on each injector.
Confirm the correct cylinder position.
Compare the codes with controller data.
Enter the correct injector codes using the proper diagnostic tool.
Check ECM configuration.
Perform calibration according to the shop manual.
Sensor Supply Voltage Error Codes
14. CA352 – Sensor Supply Voltage Low
Meaning
CA352 indicates that sensor reference voltage is too low.
Many sensors may share the same reference-voltage circuit. One shorted sensor can pull the entire circuit voltage down and create several error codes.
Possible causes
One sensor internally shorted.
Reference wire shorted to ground.
Water inside a connector.
Harness pinched.
Harness rubbing against the chassis.
ECM sensor-supply circuit failure.
Troubleshooting procedure
Measure sensor reference voltage.
Identify all sensors using the same supply circuit.
Inspect the related connectors.
Disconnect sensors one at a time according to the manual.
Monitor whether reference voltage returns to normal.
Inspect the harness for damage.
Repair the short circuit.
Inspect the ECM only after all external circuits are confirmed normal.
15. CA386 – Sensor Supply Voltage High
Meaning
CA386 indicates that sensor reference voltage is too high.
Possible causes
Reference wire shorted to battery voltage.
Alternator overcharging.
Poor controller ground.
Damaged ECM connector.
Incorrect external voltage applied.
ECM sensor-supply circuit failure.
Troubleshooting procedure
Measure battery charging voltage.
Measure sensor reference voltage.
Check for short to battery voltage.
Inspect controller ground.
Inspect the ECM connector.
Inspect all sensors connected to the supply circuit.
Repair wiring before replacing the controller.
Water-in-Fuel Sensor Error Codes
16. CA428 – Water-in-Fuel Sensor Signal High
17. CA429 – Water-in-Fuel Sensor Signal Low
The water-in-fuel sensor is commonly installed on the fuel pre-filter or water separator.
Possible causes
Water inside the fuel separator.
Sensor connector loose.
Connector contaminated by fuel, mud, or water.
Signal wire open or shorted.
Poor sensor ground.
Water-in-fuel sensor failure.
Troubleshooting procedure
Inspect the water separator.
Drain water and contamination.
Inspect fuel quality inside the tank.
Inspect the sensor connector below the filter.
Clean the connector.
Check signal wiring.
Check sensor ground.
Replace the sensor if wiring is normal but the code remains active.
A water-in-fuel sensor code indicates an electrical circuit problem, but actual water contamination must still be checked.
Engine Oil and Electrical Error Codes
18. CA435 – Engine Oil Pressure Switch Error
Meaning
CA435 indicates an abnormal engine-oil pressure-switch signal.
Possible causes
Oil-pressure switch failure.
Loose connector.
Broken wiring.
Wiring shorted.
Engine-oil level low.
Actual engine-oil pressure low.
Engine-oil filter clogged.
Engine-oil pump problem.
Troubleshooting procedure
Check engine-oil level.
Inspect for oil leakage.
Inspect the pressure-switch connector.
Check wiring continuity.
Check for short circuit.
Install a mechanical pressure gauge.
Measure actual engine-oil pressure.
Compare pressure with the correct specification.
Replace the switch if actual pressure is normal but the code remains active.
Never assume that only the pressure switch is damaged. Actual low oil pressure can seriously damage:
Crankshaft bearings.
Connecting-rod bearings.
Camshaft bearings.
Turbocharger bearings.
Other lubricated engine components.
19. CA441 – Battery Voltage Low Error
Meaning
CA441 indicates that engine-controller supply voltage is too low.
Possible causes
Weak battery.
Battery terminal loose.
Battery terminal corroded.
Poor engine ground.
Poor chassis ground.
Alternator not charging.
Alternator belt loose.
Fuse or fusible-link failure.
Excessive voltage drop.
Troubleshooting procedure
Measure battery voltage with the engine stopped.
Measure voltage during cranking.
Measure alternator output with the engine running.
Inspect battery terminals.
Check battery cable condition.
Check engine and chassis grounds.
Inspect alternator wiring.
Inspect the alternator belt.
Perform a battery load test.
Perform voltage-drop testing.
20. CA442 – Battery Voltage High Error
Meaning
CA442 indicates that engine-controller supply voltage is too high.
Possible causes
Alternator regulator failure.
Alternator overcharging.
Poor alternator ground.
Poor battery ground.
Incorrect battery connection.
Incorrect jump-start voltage.
Alternator sensing-wire problem.
Troubleshooting procedure
Measure charging voltage.
Check the alternator regulator.
Inspect alternator ground.
Inspect battery connections.
Inspect alternator sensing wiring.
Confirm that the machine has not received excessive external voltage.
Stop operation until the overvoltage problem is corrected.
Excessive voltage can damage controllers, sensors, relays, and electrical components.
Komatsu Common-Rail Error Codes
Understanding Sensor Codes and Actual Pressure Codes
Mechanics must understand the difference between a sensor-circuit code and an actual-pressure code.
| Code category | Example | Meaning |
|---|---|---|
| Sensor-circuit error | CA451, CA452 | Sensor voltage or wiring is abnormal |
| Actual-pressure error | CA449, CA553, CA559, CA2249 | Actual common-rail pressure is outside target |
This difference is extremely important.
Replacing the rail-pressure sensor will not solve an actual low-pressure condition caused by a clogged fuel filter or worn supply pump.
Similarly, replacing the supply pump will not solve a sensor wiring problem.
21. CA449 – Rail Pressure Very High Error
Meaning
CA449 indicates that actual common-rail pressure is extremely high.
Possible symptoms
Engine derate.
Unstable engine speed.
Engine stops.
Hard starting.
Abnormal fuel-system noise.
Other rail-pressure codes appear.
Possible causes
Pressure-control valve stuck.
IMV stuck.
Fuel-return line restricted.
Fuel contamination.
Rail-pressure sensor inaccurate.
Pressure-control wiring problem.
Supply-pump failure.
Troubleshooting procedure
Compare target rail pressure with actual rail pressure.
Inspect related IMV codes.
Inspect rail-pressure sensor codes.
Check the pressure-control valve connector.
Inspect the fuel-return line.
Inspect fuel quality.
Check for fuel contamination.
Test the IMV or control valve.
Test the supply pump according to the manual.
Stop operation if rail pressure cannot be controlled.
22. CA451 – Rail Pressure Sensor Signal High
Meaning
CA451 indicates that rail-pressure sensor signal voltage is too high.
Possible causes
Signal wire shorted to reference voltage.
Sensor ground open.
Connector loose.
Connector corroded.
Rail-pressure sensor failure.
ECM internal circuit problem.
Troubleshooting procedure
Inspect the rail-pressure sensor connector.
Measure reference voltage.
Check sensor ground.
Check the signal wire for short to voltage.
Check rail-pressure data before starting the engine.
Compare the reading with expected atmospheric conditions.
Replace the sensor if wiring is normal but the signal remains incorrect.
23. CA452 – Rail Pressure Sensor Signal Low
Meaning
CA452 indicates that rail-pressure sensor signal voltage is too low.
Possible causes
Signal wire shorted to ground.
Sensor power-supply circuit open.
Connector disconnected.
Sensor ground problem.
Rail-pressure sensor failure.
ECM circuit failure.
Troubleshooting procedure
Inspect the sensor connector.
Check reference voltage.
Check sensor ground.
Check signal-wire continuity.
Check for short circuit to ground.
Inspect the connector terminals.
Replace the sensor only after the wiring is confirmed normal.
24. CA553 – Rail Pressure High Error
Meaning
CA553 indicates that actual common-rail pressure is higher than the pressure commanded by the engine controller.
Possible causes
IMV stuck.
Pressure-control valve stuck.
Fuel-return restriction.
Control valve contaminated.
Rail-pressure sensor biased.
Supply-pump problem.
Wiring fault.
Troubleshooting procedure
Compare target and actual rail pressure.
Check IMV command.
Check control-valve current.
Inspect fuel-return restriction.
Inspect the control-valve connector.
Check fuel contamination.
Test the control valve.
Test the supply pump if necessary.
25. CA559 – Common Rail Pressure Low Error
Meaning
CA559 generally indicates that actual common-rail pressure is lower than the pressure required by the engine controller.
Common symptoms
Low engine power.
Engine difficult to start.
Engine stalls under load.
Engine speed does not reach high idle.
Engine enters derate mode.
Acceleration is slow.
CA2249 may appear afterward.
Possible causes
Fuel level too low.
Poor fuel quality.
Water in the fuel.
Fuel pre-filter clogged.
Main fuel filter clogged.
Fuel-tank breather blocked.
Suction hose restricted.
Suction hose leaking.
Air entering the fuel system.
Feed pump weak.
IMV malfunction.
Supply pump worn.
Excessive injector return flow.
Rail-pressure sensor inaccurate.
Pressure-control valve leaking.
Troubleshooting sequence
Check fuel level.
Inspect fuel quality.
Drain the water separator.
Inspect the fuel pre-filter.
Inspect the main fuel filter.
Check the fuel-tank breather.
Inspect the suction hose.
Check for air entering the system.
Prime the fuel system.
Measure low-pressure fuel supply.
Compare target and actual rail pressure.
Inspect the IMV connector.
Inspect the rail-pressure sensor connector.
Perform an injector return-flow test.
Test the pressure-control valve.
Inspect the supply pump only after the low-pressure system is confirmed normal.
Do not replace the supply pump immediately when CA559 appears.
26. CA2249 – Common Rail Pressure Very Low Error
Meaning
CA2249 indicates that common-rail pressure is extremely low.
On certain models, the controller may limit engine output to protect the engine and fuel system.
Possible symptoms
Engine does not start.
Engine starts and then stops.
Severe engine-power loss.
Engine stalls under load.
Engine derate.
Rail pressure fails to increase during cranking.
Possible causes
Fuel tank empty.
Fuel filter severely clogged.
Fuel contaminated by water or dirt.
Suction hose leaking.
Air entering the fuel system.
Feed pump not working.
IMV stuck.
IMV electrical circuit problem.
Supply pump not generating pressure.
Excessive injector leak-off.
Pressure-control valve leaking.
Rail-pressure sensor problem.
Troubleshooting procedure
Do not replace the supply pump immediately.
Check fuel level.
Check fuel quality.
Drain the water separator.
Replace clogged filters.
Inspect the suction line from the tank.
Check the fuel-tank breather.
Check for air bubbles in the fuel system.
Measure feed pressure.
Inspect the IMV connector.
Measure IMV resistance.
Compare target and actual rail pressure during cranking.
Perform an injector return-flow test.
Inspect the pressure-control valve.
Test the supply pump according to the correct shop manual.
Engine Speed Sensor Error Codes
27. CA689 – Engine Ne Speed Sensor Error
Meaning
CA689 indicates an abnormal crankshaft or engine-speed sensor signal.
Possible causes
Crankshaft sensor failure.
Connector loose.
Wiring open.
Wiring shorted.
Metal particles on the sensor.
Incorrect sensor air gap.
Damaged sensing ring.
Sensing ring loose.
Troubleshooting procedure
Monitor engine speed during cranking.
Inspect the crankshaft sensor connector.
Clean the sensor tip.
Check wiring continuity.
Check for short circuit.
Inspect sensor mounting.
Inspect the sensing ring.
Replace the sensor if its output is outside specification.
28. CA731 – Backup Speed Sensor Phase Error
Meaning
CA731 indicates that the phase relationship between the crankshaft speed sensor and backup speed sensor is incorrect.
Possible causes
Crankshaft sensor weak.
Camshaft sensor weak.
Sensor installed incorrectly.
Sensing ring shifted.
Sensing ring loose.
Mechanical timing problem.
Wiring problem.
Connector problem.
Troubleshooting procedure
Inspect both speed sensors.
Check crankshaft-sensor output.
Check camshaft-sensor output.
Inspect both connectors.
Inspect the sensing rings.
Check mechanical timing if necessary.
Repair wiring.
Retest while cranking.
29. CA778 – Engine Backup Speed Sensor Error
Meaning
CA778 indicates an abnormal backup or camshaft speed-sensor signal.
Troubleshooting procedure
Inspect the camshaft sensor connector.
Inspect wiring to the ECM.
Clean the sensor tip.
Measure sensor resistance or output.
Check sensor mounting.
Check sensor air gap.
Inspect the sensing ring.
Inspect sensing-ring mounting bolts.
Throttle Supply Voltage Error Codes
30. CA2185 – Throttle Sensor Supply Voltage High
31. CA2186 – Throttle Sensor Supply Voltage Low
Possible causes
Reference-voltage circuit shorted.
Throttle sensor internally shorted.
Wiring shorted to battery voltage.
Wiring shorted to ground.
Poor connector condition.
Other sensors on the same circuit causing a fault.
ECM sensor-supply failure.
Troubleshooting procedure
Measure throttle-sensor supply voltage.
Inspect the fuel-control dial.
Inspect the connector.
Check sensor ground.
Check wiring for short to battery voltage.
Check wiring for short to ground.
Inspect other sensors sharing the same supply circuit.
Inspect the controller only after external circuits are normal.
Intake-Air Heater Error Codes
32. CA2555 – Intake-Air Heater Relay Open Circuit
Meaning
CA2555 indicates an open circuit in the intake-air heater or preheater-relay control circuit.
Possible causes
Relay coil open.
Relay connector disconnected.
Fuse blown.
Control wire broken.
Connector corroded.
ECM relay-driver circuit failure.
Troubleshooting procedure
Check the preheater fuse.
Inspect the intake-heater relay.
Check relay power supply.
Check the control wire from the ECM.
Measure relay-coil resistance.
Inspect the heater connector.
Replace the relay if its coil is open.
33. CA2556 – Intake-Air Heater Relay Short Circuit
Meaning
CA2556 indicates a short circuit in the preheater-relay control circuit.
Possible causes
Relay coil shorted.
Control wire shorted to ground.
Damaged wiring insulation.
Melted connector.
Incorrect fuse capacity.
ECM relay-driver problem.
Troubleshooting procedure
Measure relay-coil resistance.
Inspect wiring for damaged insulation.
Check the control wire for short to ground.
Inspect the relay connector.
Confirm the correct fuse specification.
Replace the relay if its resistance is outside specification.
Komatsu Warning Codes
In addition to CA codes, some Komatsu monitors display system-warning codes.
| Code | Meaning |
|---|---|
| AA10NX | Air cleaner clogged |
| AB00KE | Charging voltage low |
| B@BAZG | Engine-oil pressure low |
| B@BAZK | Engine-oil level low |
| B@BCNS | Engine coolant overheat |
| B@BCZK | Radiator coolant level low |
| B@HANS | Hydraulic oil overheat |
AA10NX – Air Cleaner Clogging
Possible causes
Primary air filter clogged.
Safety filter clogged.
Intake hose restricted.
Intake hose collapsed.
Air-cleaner restriction switch failure.
Sensor wiring problem.
Troubleshooting procedure
Check the air-filter restriction indicator.
Inspect the primary filter.
Clean or replace the primary filter according to the manual.
Inspect the safety filter.
Do not repeatedly clean the safety filter.
Inspect the intake hose.
Inspect the restriction switch and wiring.
Recheck the warning after repair.
AB00KE – Charging Voltage Low
Possible causes
Alternator not charging.
Alternator belt loose.
Alternator belt broken.
Battery weak.
Battery terminals loose.
Charging fuse blown.
Alternator wiring damaged.
Poor alternator ground.
Troubleshooting procedure
Inspect the alternator belt.
Measure battery voltage.
Measure charging voltage.
Inspect the alternator B+ cable.
Inspect battery terminals.
Inspect engine and chassis grounds.
Check the alternator regulator.
Perform a battery load test.
B@BAZG – Engine Oil Pressure Low
This warning indicates that engine-oil pressure is too low.
Immediate action
Stop the machine in a safe location.
Reduce engine speed.
Shut down the engine if pressure remains low.
Check engine-oil level.
Inspect for oil leakage.
Inspect the engine-oil filter.
Measure actual pressure with a mechanical gauge.
Inspect the oil pump.
Inspect the suction strainer.
Inspect the pressure-relief valve.
Inspect engine-bearing clearance if pressure remains low.
Do not continue operating an engine with low oil pressure.
B@BAZK – Engine Oil Level Low
Possible causes
Engine-oil level below specification.
External oil leakage.
Oil consumption.
Incorrect oil filling.
Oil-level sensor failure.
Sensor wiring problem.
Troubleshooting procedure
Park the machine on level ground.
Allow the oil to settle.
Check the dipstick.
Add the correct engine oil if necessary.
Inspect for leaks.
Inspect the oil-level sensor.
Inspect sensor wiring.
B@BCNS – Engine Coolant Overheat
Possible causes
Coolant level low.
Radiator clogged.
Cooling fan speed low.
Fan belt loose.
Thermostat stuck.
Water pump damaged.
Radiator cap defective.
Cooling-system leakage.
Excessive engine load.
Combustion gas entering the cooling system.
Troubleshooting procedure
Reduce engine load.
Park the machine in a safe location.
Allow the engine to idle according to the operating manual.
Do not immediately open the radiator cap.
Wait until coolant temperature decreases.
Check coolant level.
Inspect for coolant leakage.
Clean the radiator.
Check fan speed.
Inspect the thermostat.
Inspect the water pump.
Test the radiator cap.
Perform a cooling-system pressure test.
B@BCZK – Radiator Coolant Level Low
Possible causes
Coolant leakage.
Radiator level low.
Reservoir level low.
Hose damaged.
Clamp loose.
Water-pump leakage.
Coolant-level switch failure.
Wiring problem.
Troubleshooting procedure
Check coolant level when the engine is cold.
Inspect the radiator.
Inspect the reservoir.
Inspect hoses and clamps.
Inspect the water pump.
Inspect the radiator cap.
Inspect the coolant-level sensor.
Perform a cooling-system pressure test.
B@HANS – Hydraulic Oil Overheat
Meaning
B@HANS indicates that hydraulic-oil temperature is too high.
Possible symptoms
Hydraulic movement becomes slow.
Hydraulic power decreases.
Pump noise increases.
Oil temperature warning appears.
Hydraulic oil smells burnt.
Machine cycle time increases.
Possible causes
Hydraulic-oil level low.
Incorrect hydraulic oil.
Hydraulic cooler clogged.
Cooling fan speed low.
Hydraulic filter clogged.
Relief valve operating continuously.
Main pump efficiency low.
Internal leakage excessive.
Hydraulic cylinder internal leakage.
Motor internal leakage.
Incorrect attachment operation.
Temperature sensor inaccurate.
Troubleshooting procedure
Reduce hydraulic load.
Park the machine safely.
Check hydraulic-oil level.
Check for leakage.
Inspect hydraulic-oil condition.
Clean the hydraulic cooler.
Check cooling-fan speed.
Inspect hydraulic filters.
Measure hydraulic pressure.
Check whether the relief valve is operating continuously.
Perform a hydraulic cycle-time test.
Perform pump case-drain testing if necessary.
Perform motor case-drain testing if necessary.
Inspect internal leakage in cylinders and control valves.
How to Read Komatsu Error Codes Correctly
1. Record the complete error code
Do not record only the action level such as L01, L02, or L03.
Record the complete code, for example:
CA559.
CA2249.
CA451.
CA122.
B@BCNS.
B@HANS.
The action level shows the urgency of the problem, while the detailed code identifies the affected system.
2. Record the machine condition
Record the operating condition when the code appears.
Important information includes:
Engine cold or hot.
Engine at low idle or high idle.
Machine digging or traveling.
Swing operation active.
Heavy load or light load.
Code active continuously or intermittently.
Engine power normal or low.
Smoke color.
Abnormal noise.
Temperature condition.
Recent maintenance or component replacement.
3. Check active and stored codes
An active code means that the fault is still detected.
A stored code means that the fault occurred previously but may not currently be active.
Do not erase codes before recording:
Code number.
Occurrence time.
Machine hours.
Operating condition.
Related symptoms.
Other codes appearing at the same time.
4. Perform basic inspections first
Before performing advanced testing, inspect:
Engine-oil level.
Coolant level.
Hydraulic-oil level.
Fuel level.
Fuel quality.
Battery condition.
Fuses.
Relays.
Connectors.
Wiring.
Hoses.
Filters.
Fluid leakage.
Air leakage.
Ground connections.
Many expensive component replacements can be avoided by performing these basic checks correctly.
5. Use monitoring data
Monitoring data allows mechanics to compare controller commands with actual machine conditions.
Useful monitoring data may include:
Target rail pressure.
Actual rail pressure.
Engine speed.
Coolant temperature.
Intake-air temperature.
Boost pressure.
Battery voltage.
Throttle percentage.
Hydraulic pump pressure.
Sensor supply voltage.
Injector correction value.
6. Separate sensor-circuit faults from actual system faults
Examples:
CA451 indicates high rail-pressure sensor signal.
CA449 indicates actual rail pressure is extremely high.
CA144 indicates high coolant-temperature sensor signal.
B@BCNS indicates actual engine overheat.
CA123 indicates low boost-sensor signal.
Actual low boost may be caused by air-filter, turbocharger, or hose problems.
Understanding this difference prevents incorrect component replacement.
7. Follow a systematic troubleshooting sequence
A recommended sequence is:
Visual inspection → fluid level → filter condition → connector → wiring → fuse and relay → power supply → ground → sensor signal → actual pressure or temperature → actuator → controller.
Start with the simplest and most likely causes before replacing expensive parts.
Common Mistakes When Troubleshooting Komatsu Error Codes
Replacing the sensor immediately
A sensor code does not automatically mean that the sensor is damaged.
The problem may be caused by:
Loose connector.
Broken wire.
Short circuit.
Poor ground.
Incorrect reference voltage.
Water inside the connector.
Controller problem.
Erasing the code before recording data
Clearing the code too early may remove valuable information needed to identify the root cause.
Always record the code and operating condition first.
Replacing the supply pump when CA559 appears
CA559 may be caused by:
Clogged fuel filter.
Air entering the system.
Blocked tank breather.
Suction restriction.
Low feed pressure.
Excessive injector return flow.
IMV problems.
Rail-pressure sensor problems.
The supply pump should only be replaced after proper testing.
Ignoring battery-voltage codes
Low or unstable battery voltage can trigger several sensor and communication codes at the same time.
Always correct battery and charging-system problems first.
Using code definitions from a different machine model
A code on a PC200-8 may not use the same connector pins, standard values, or troubleshooting procedure as a PC200-10, PC400-11, HD785, WA600, or D375.
Always use the correct manual.
Replacing the ECM too early
The ECM should normally be checked after confirming:
Battery voltage.
Charging voltage.
Ground circuit.
Fuses.
Relays.
Sensor supply.
Sensor output.
Actuator circuit.
Connector condition.
Wiring continuity.
When Should the Machine Be Stopped Immediately?
Stop and secure the machine if any of the following conditions occur:
Engine-oil pressure is low.
Engine coolant is overheating.
Hydraulic oil is severely overheating.
Electrical voltage is excessively high.
Burnt wiring or connectors are found.
The engine produces a knocking sound.
The engine loses power severely.
The engine stops repeatedly.
Common-rail pressure cannot be controlled.
Heavy smoke appears with abnormal noise.
A red critical warning appears.
Any decision to continue operation must follow:
Monitor action level.
Company safety procedures.
Operation and Maintenance Manual.
Shop Manual instructions.
Supervisor or technical-department approval.
Conclusion
Komatsu error codes can greatly improve troubleshooting efficiency when they are interpreted correctly.
However, an error code should not be used as the only reason to replace a sensor, injector, supply pump, controller, or other expensive component.
Codes such as:
CA122.
CA123.
CA144.
CA145.
CA451.
CA452.
Generally point toward sensor-circuit or electrical-signal problems.
Codes such as:
CA449.
CA553.
CA559.
CA2249.
Relate more directly to actual common-rail pressure being outside the required range.
The correct troubleshooting process is:
Record the code → inspect the machine condition → check fluid levels and filters → inspect connectors and wiring → measure power supply and ground → analyze monitoring data → perform system testing → identify the root cause.
Always use the correct Komatsu Shop Manual or Operation and Maintenance Manual based on the machine model and serial number.
A systematic diagnostic method helps mechanics:
Avoid incorrect diagnosis.
Reduce unnecessary component replacement.
Shorten machine downtime.
Reduce maintenance costs.
Improve equipment reliability.
Prevent more serious component damage.
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