Applicable Systems
EMCP 4.2
Symptoms
CID 478 (Work Light Circuit): Abnormal update rate. The Caterpillar Electronic Technician (Cat ET) displays this fault. Machine operation may be derated or shut down depending on severity.
Possible Causes
- Sensor or actuator for Work Light Circuit failed or out of range
- Wiring harness for CID 478 circuit open, shorted, or corroded
- ECM parameter for Work Light Circuit out of calibration
- Mechanical or hydraulic issue affecting the component
Troubleshooting Steps
- Step 1: Connect Cat ET and read active fault codes for CID 478
Fault code 478-9 displayed with timestamp and component data - Step 2: Inspect wiring harness and connector for CID 478 (Work Light Circuit)
Wiring intact, connector clean and seated - Step 3: Test Work Light Circuit sensor or actuator output
Output within Caterpillar specification range - Step 4: Check ECM for stored parameters and calibrate if needed
Parameters within factory specification - Step 5: Clear fault with Cat ET and verify no re-occurrence
Fault cleared and does not return after test cycle
How to Reset
To reset: 1) Correct the underlying fault for CID 478. 2) Press FAULT RESET on the EMCP panel or clear via Cat ET. 3) Verify machine returns to normal operation. Caution: Do not reset without repairing the fault as the machine may operate in derated mode.
Frequently Asked Questions
- Q: What does CID 478 mean on Caterpillar equipment?
CID 478 refers to Work Light Circuit. It is a standard Caterpillar Component Identifier used in diagnostic systems.
- Q: What does FMI 9 mean?
FMI 9 indicates: Abnormal update rate. FMI (Failure Mode Identifier) describes the type of failure detected.
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Source: Caterpillar SAE J1939 CID/FMI Reference, wholefleet.ca/motorsymphdiesel.com
Category: Generator
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