Diagnosis & Repair
- Inspect circuits between ECM and oxygen sensor for opens or shorts. See wiring diagram in the WIRING DIAGRAMS article. Repair as needed. If all circuits are okay, connect scan tester. See Figure.
- Start engine and warm to normal operating temperature. Monitor heated oxygen sensor output voltage and short-term fuel trim. If scan tester indicates a lean condition (.55 volt or less, +20 trim) or rich condition (.4 volt or more, -20 trim), see CODE P0170 - FUEL TRIM MALFUNCTION.
- If scan tester indicates other than in step 2), operate engine at 2500 RPM for 90 seconds. Monitor oxygen sensor voltage. If voltage constantly fluctuates in wide range (.3-.9 volt), repeat Test Drive Confirmation. If voltage does NOT fluctuate, or stays in narrow range, replace sensor and retest.