Applicable Systems
EMCP 4.2
Symptoms
CID 321 (Heated Oxygen Sensor Bank 2): Condition exists. 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 Heated Oxygen Sensor Bank 2 failed or out of range
- Wiring harness for CID 321 circuit open, shorted, or corroded
- ECM parameter for Heated Oxygen Sensor Bank 2 out of calibration
- Mechanical or hydraulic issue affecting the component
Troubleshooting Steps
- Step 1: Connect Cat ET and read active fault codes for CID 321
Fault code 321-31 displayed with timestamp and component data - Step 2: Inspect wiring harness and connector for CID 321 (Heated Oxygen Sensor Bank 2)
Wiring intact, connector clean and seated - Step 3: Test Heated Oxygen Sensor Bank 2 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 321. 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 321 mean on Caterpillar equipment?
CID 321 refers to Heated Oxygen Sensor Bank 2. It is a standard Caterpillar Component Identifier used in diagnostic systems.
- Q: What does FMI 31 mean?
FMI 31 indicates: Condition exists. 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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