Diagnosis & Repair
- Inspect circuits between ECM and oxygen sensor for opens or shorts. See wiring diagram in the WIRING DIAGRAMS - 2.7L 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.