Possible Causes
| Possible Causes |
|---|
| (K902) O2 RETURN UPSTREAM CIRCUIT SHORTED TO GROUND |
| (K904) O2 RETURN DOWNSTREAM CIRCUIT SHORTED TO GROUND |
| (K902) O2 RETURN UPSTREAM CIRCUIT OPEN |
| (K904) O2 RETURN DOWNSTREAM CIRCUIT OPEN |
| EXHAUST LEAK |
| ENGINE MECHANICAL CONDITION |
| AGING O2 SENSOR |
| CATALYTIC CONVERTER |
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Refer to PRE-DIAGNOSTIC TROUBLESHOOTING PROCEDURE .