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Diagnosis & Repair

  1. Connect scan tool to Data Link Connector (DLC) No. 3. See Figure. Start engine and warm to normal operating temperature. Using scan tool, monitor banks No. 1 and No. 2, heated oxygen sensor No. 1. Snap accelerate engine 3 times to 4000 RPM. Heater oxygen sensors should indicate a rich signal (.45 volt or more) at least once.
  2. If a rich signal is indicated for both heated oxygen sensors, replace ECM and retest. If either heated oxygen sensor does not display a rich signal, check for an open or short circuit in wiring harness and connector between ECM E16 connector and appropriate heated oxygen sensor. See appropriate wiring diagram in SYSTEM WIRING DIAGRAMS article. Repair as necessary. If wiring harness is okay, go to next step.
  3. Check for misfire. See DTC P0300-P0308:  RANDOM MISFIRE DETECTED. Repair as necessary. If misfire is not detected, check for exhaust system leaks. If exhaust system is okay, replace suspect heater oxygen sensor and retest.
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