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DTC P0138

DTC P0138  HO2S circuit high input 
DETECTION CONDITION 
  • The PCM monitors input voltage from the HO2S. If the input voltage from the HO2S is above 1.2 V  or HO2S bias voltage above 1.8 V for 5s  , the PCM determines that the HO2S circuit input is high.

Diagnostic support note 
  • This is a continuous monitor (A/F sensor, HO2S).
  • The MIL illuminates if the PCM detects the above malfunction condition in two consecutive drive cycles or in one drive cycle while the DTC for the same malfunction has been stored in the PCM.
  • PENDING CODE is available if the PCM detects the above malfunction condition during the first drive cycle.
  • FREEZE FRAME DATA (Mode 2/Mode 12) is available.
  • The DTC is stored in the PCM memory.
POSSIBLE CAUSE 
  • HO2S connector or terminals malfunction
  • PCM connector or terminals malfunction
  • Short to power supply in wiring harness between HO2S terminal A and PCM terminal 2Q
  • HO2S malfunction
  • PCM malfunction
G07877622
DIAGNOSTIC PROCEDURE

STEP INSPECTION ACTION
1 VERIFY FREEZE FRAME DATA (MODE 12) AND DIAGNOSTIC MONITORING TEST RESULTS HAVE BEEN RECORDED 
  • Have the FREEZE FRAME DATA (Mode 12) and DIAGNOSTIC MONITORING TEST RESULTS (A/F sensor, HO2S related) been recorded?
 Yes Go to the next step.
No Record the FREEZE FRAME DATA (Mode 12) and DIAGNOSTIC MONITORING TEST RESULTS on the repair order, then go to the next step.
2 VERIFY RELATED SERVICE BULLETINS AVAILABILITY 
  • Verify related Service Bulletins availability.
  • Is any related Service Bulletins available?
 Yes Perform the repair or diagnosis according to the available Service Bulletins.
  • If the vehicle is not repaired, go to the next step.
No Go to the next step.
3 VERIFY RELATED PENDING CODE AND STORED DTC 
  • Turn the ignition switch off, then to the ON position (Engine off).
  • Verify related PENDING CODE and stored DTC.
  • Are any DTCs present?
 Yes Go to the applicable DTC inspection.
(See DTC TABLE ).
No Go to the next step.
4 IDENTIFY TRIGGER DTC FOR FREEZE FRAME DATA (MODE 2) 
  • Is the DTC P0138 on FREEZE FRAME DATA (Mode 2)?
 Yes Go to the next step.
No Go to the troubleshooting procedures for DTC on FREEZE FRAME DATA (Mode 2).
(See DTC TABLE ).
5 INSPECT HO2S CONNECTOR AND TERMINALS 
  • Turn the ignition switch off.
  • Disconnect the HO2S connector.
  • Inspect for poor connection (such as damaged/pulled-out pins, corrosion).
  • Is there any malfunction?
 Yes Repair or replace the connector or terminals, then go to Step 9.
No Go to the next step.
6 INSPECT PCM CONNECTOR AND TERMINALS 
  • Disconnect the PCM connector.
  • Inspect for poor connection (such as damaged/pulled-out pins, corrosion).
  • Is there any malfunction?
 Yes Repair or replace the connector or terminals, then go to Step 9.
No Go to the next step.
7 INSPECT HO2S SIGNAL CIRCUIT FOR SHORT TO POWER SUPPLY 
  • HO2S and PCM connectors are disconnected.
  • Turn the ignition switch to the ON position (Engine off).
  • Measure the voltage between HO2S terminal A (wiring harness-side) and body ground.
  • Is there any voltage?
 Yes Repair or replace the wiring harness for a possible short to power supply, then go to Step 9.
No Go to the next step.
8 INSPECT HO2S 
 Yes Replace the HO2S, then go to the next step.
(See HEATED OXYGEN SENSOR (HO2S) REMOVAL/INSTALLATION ).
No Go to the next step.
9 VERIFY TROUBLESHOOTING OF DTC P0138 COMPLETED 
  • Make sure to reconnect all disconnected connectors.
  • Clear the DTC from the PCM memory using the M-MDS.
  • Perform the KOEO or KOER self test (using M-MDS) or Drive Mode 03 (PCM Adaptive Memory Production, EGR System, A/F Sensor Heater, HO2S Heater, A/F Sensor, HO2S, and TWC Repair Verification Drive Mode) (not using M-MDS).

    (See KOEO/KOER SELF TEST ).

    (See OBD-II DRIVE MODE ).

  • Is the PENDING CODE for this DTC present?
 Yes Replace the PCM, then go to the next step.
(See PCM REMOVAL/INSTALLATION ).
No Go to the next step.
10 VERIFY AFTER REPAIR PROCEDURE 
 Yes Go to the applicable DTC inspection.
(See DTC TABLE ).
No DTC troubleshooting completed.
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