Applicable Systems
EMCP 4.2
Symptoms
CID 326 (DEF Dosing Unit): Data valid but below normal operating range. 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 DEF Dosing Unit failed or out of range
- Wiring harness for CID 326 circuit open, shorted, or corroded
- ECM parameter for DEF Dosing Unit out of calibration
- Mechanical or hydraulic issue affecting the component
Troubleshooting Steps
- Step 1: Connect Cat ET and read active fault codes for CID 326
Fault code 326-1 displayed with timestamp and component data - Step 2: Inspect wiring harness and connector for CID 326 (DEF Dosing Unit)
Wiring intact, connector clean and seated - Step 3: Test DEF Dosing Unit 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 326. 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 326 mean on Caterpillar equipment?
CID 326 refers to DEF Dosing Unit. It is a standard Caterpillar Component Identifier used in diagnostic systems.
- Q: What does FMI 1 mean?
FMI 1 indicates: Data valid but below normal operating range. 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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