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Diagnosis & Repair Procedure

NOTE: For better performance and results of this diagnostic procedure, usage of appropriate wiring diagram is recommended. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.
NOTE: Perform all voltage and resistance tests using a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure. Use an ohmmeter to isolate wiring harness shorts or opens.
  1. If engine system check has been performed, go to next step. If engine system check has not been performed, perform A-4: ENGINE SYSTEM CHECK  under SYSTEM TESTS, then go to next step.
  2. Start engine and allow it to reach normal operating temperature. Race engine speed up to 2000 RPM for 60 seconds. While revving engine 5 or 6 times, observe on scan tool HO2S-2 values. If HO2S-2 voltage does not deflect from below 0.3 volt to over 0.6 volt, go to next step. If HO2S-2 voltage does not deflect from below 0.3 volt to over 0.6 volt, go to step  4 .
  3. Turn ignition switch to LOCK position. Disconnect HO2S-2 4-pin harness connector C54, located between exhaust manifold and front catalytic converter. See Figure . Start engine and allow it to reach normal operating temperature. Race engine speed up to 2000 RPM for 60 seconds. While revving engine 5 or 6 times, measure voltage between HO2S-2 pigtail connector terminals No. 1 and 2 (component side). See Figure . If HO2S-2 voltage does not deflect from below 0.3 volt to over 0.6 volt, replace HO2S-2. See HEATED OXYGEN SENSORS NO. 1 & 2 under ENGINE SENSORS & SWITCHES in REMOVAL & INSTALLATION article. If HO2S-2 voltage does not deflect from below 0.3 volt to over 0.6 volt, check for open or short circuit in Red/Green wire and Gray/Yellow wire between ECM and HO2S-12. If open or short circuit is found, repair as necessary. After repair, repeat DTC CONFIRMATION TEST  . If open or short circuit is not found, substitute ECM with a known good unit and repeat DTC CONFIRMATION TEST  .
  4. Race engine speed up to 2000 RPM for 60 seconds. Reduce engine speed. With engine idling and using scan tool, check short term fuel trim value. If value is between -20 and +20 percent, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES article. If value is not between -20 and +20 percent, perform diagnose and repair procedure for DTC P0171 OR DTC P0172  . After repair, repeat DTC CONFIRMATION TEST  .
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