8904

Possible Causes

• •Engine related problem
• •Fuel system related problem
• •Power is noisy due to a failed alternator
• •Supply voltage problem where the ECM is unable to monitor noise via the low-passed supply feedback
• •UEGO internal supply voltage is low
• •UEGO processing circuitry supply voltage is too low for normal operation while Vbat or Vrelay low-pass filtered voltage is > 9.0V

Suggested Actions

1. 1Inspect alternator and repair/replace as needed
2. 2Perform OBD system check
3. 3Replace ECM and re-test
4. 4Replace UEGO sensor and re-test
5. 5Troubleshoot supply voltage source and repair/replace as needed
6. 6Verify the operation of the MIL

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