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2008 - MX-5 - Engine

DTC P0138 [LF]



DTC P0138

Rear HO2S circuit high input

DETECTION CONDITION

  • The PCM monitors input voltage from rear HO2S. If the input voltage from the rear HO2S sensor is above 1.2 V for 0.8 s, the PCM determines that circuit input is high.

    Diagnostic support note
  • This is a continuous monitor (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 is available.

  • The DTC is stored in the PCM memory.

POSSIBLE CAUSE

  • Rear HO2S malfunction

  • Short to power supply in wiring harness between rear HO2S terminal A and PCM terminal 2Q

  • Rear HO2S or PCM terminal shorted

  • PCM malfunction


Diagnostic procedure

STEP

INSPECTION

ACTION

1

VERIFY FREEZE FRAME DATA AND DIAGNOSTIC MONITORING TEST RESULTS HAVE BEEN RECORDED
  • Have FREEZE FRAME DATA and DIAGNOSTIC MONITORING TEST RESULTS (HO2S related) been recorded?

Yes

Go to the next step.

No

Record the FREEZE FRAME DATA and DIAGNOSTIC MONITORING TEST RESULTS on the repair order, then go to the next step.

2

VERIFY RELATED REPAIR INFORMATION AVAILABILITY
  • Verify related Service Bulletins and/or on-line repair information availability.

  • Is any related repair information available?

Yes

Perform repair or diagnosis according to the available repair information.

  • If the vehicle is not repaired, go to the next step.

No

Go to the next step.

3

VERIFY RELATED PENDING OR STORED DTC
  • Turn the ignition switch off, then to the ON position. (Engine off)

  • Verify pending code or stored DTCs using M-MDS.

  • Is other DTC present?

Yes

Go to the appropriate DTC troubleshooting procedures.

(See DTC TABLE [LF].)

No

Go to the next step.

4

IDENTIFY TRIGGER DTC FOR FREEZE FRAME DATA
  • Is DTC P0138 on FREEZE FRAME DATA?

Yes

Go to the next step.

No

Go to troubleshooting procedures for DTC on FREEZE FRAME DATA.

(See DTC TABLE [LF].)

5

INSPECT REAR HO2S SIGNAL CIRCUIT FOR SHORT TO POWER SUPPLY
  • Turn the ignition switch off.

  • Disconnect rear HO2S connector.

  • Turn the ignition switch to the ON position. (Engine off)

  • Measure the voltage between rear HO2S terminal A (wiring harness-side) and body ground.

  • Is there any voltage?

Yes

Replace short to power supply, then go to Step 7.

No

Go to the next step.

6

INSPECT REAR HO2S

Yes

Go to the next step.

No

Replace sensor, then go to the next step.

(See REAR HEATED OXYGEN SENSOR (HO2S) REMOVAL/INSTALLATION [LF].)

7

VERIFY TROUBLESHOOTING OF DTC P0138 COMPLETED
  • Make sure to reconnect all disconnected connectors.

  • Turn the ignition switch to the ON position. (Engine off)

  • Clear the DTC from the memory using the M-MDS.

  • Run the KOEO self-test with M-MDS, or PCM adaptive memory procedure drive mode and HO2S heater, HO2S, and TWC repair verification drive mode.

    (SeeKOEO/KOER SELF TEST [LF].)

    (See OBD-II DRIVE MODE [LF].)

  • Is the PENDING CODE for this DTC present?

Yes

Replace the PCM, then go to the next step.

(See PCM REMOVAL/INSTALLATION [LF].)

No

Go to the next step.

8

VERIFY AFTER REPAIR PROCEDURE

Yes

Go to the applicable DTC troubleshooting.

(See DTC TABLE [LF].)

No

Troubleshooting completed.




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