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Home >> Nissan-Datsun >> 2003 >> Sentra Limited >> Repair and Diagnosis >> External Pages >> Different car >> Section 40 (Engine Controls - Self-Diagnostics - 2.5) >> Diagnostic Tests >> DTC PO139: Rear Heated Oxygen Sensor Slow Response >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2002 Nissan Sentra. However, it is still accessible from the selected car via links, so may be relevant.
  1. Turn ignition off. Loosen and retighten engine ground bolts. See Figure and Figure . Go to next step.
  2. Start engine and warm engine to normal operating temperature. Turn ignition off. Disconnect MAF sensor harness connector. Start engine and let it idle for at least 5 seconds. Turn ignition off and reconnect MAF sensor harness connector. Go to next step.
  3. Ensure first trip DTC P0102 is set. Clear DTCs. Start engine and let it idle for at least 10 minutes. Recheck for DTCs. If DTC P0171 or P0172 is present and engine is hard to start, perform diagnosis for DTC P0171 or P0172. See DTC P0171 OR DTC P0172 . If DTC P0171 or P0172 is not present and engine is not hard to start, go to next step.
  4. Turn ignition off. Disconnect rear HO2S harness connector. See Figure. Check continuity between ground and rear HO2S harness connector terminal No. 4 (Black wire). Continuity should exist. Turn ignition on. Measure voltage between ground and rear HO2S harness connector terminal No. 4 (Black wire). Voltage should be less than 0.5 volt. If circuit checks are not as specified, repair open or short circuit to voltage in Black wire between ground and rear HO2S harness connector terminal No. 4. Perform DTC CONFIRMATION TEST  to verify repair. If circuit checks are as specified, go to next step.
  5. Turn ignition off. Disconnect ECM harness connector. Check continuity of White wire between ECM harness connector terminal No. 95 and rear HO2S harness connector terminal No. 1. See Figure and Figure . Continuity should exist. Also, check circuit for short to ground and short to voltage. Repair circuit as necessary and perform DTC CONFIRMATION TEST  to verify repair. If circuit is okay, go to next step.
    6. CAUTION: DO NOT use ECM ground terminals when measuring voltage.
  6. Reconnect all harness connectors. Drive vehicle at a speed of more than 43 MPH for 2 consecutive minutes. Stop vehicle and leave engine running. Measure voltage between ground and ECM terminal No. 95 (White wire) by backprobing. While observing voltage, quickly increase engine speed to 4000 RPM at least 10 times. If voltage increases to more than 0.63 volt at least one time, go to step  7. If voltage does not increase to more than 0.63 volt, go to next step.
  7. Idle engine for 10 minutes and recheck voltage. Or, drive vehicle and coast from 50 MPH with transmission in 3rd gear (M/T) or in "D" with "OD" turned off (A/T) and recheck voltage. Voltage should decrease to less than 0.50 volt at least once during this test. If voltage decreases to than 0.50 volt at least once, go to next step. If voltage still does not decrease to less than 0.50 volt at least one time, replace rear HO2S and perform DTC CONFIRMATION TEST  to verify repair.
  8. No problem is indicated at this time. Problem may be intermittent. See INTERMITTENTS in TROUBLESHOOTING - NO CODES article.
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