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Home >> Mazda >> 2006 >> MX-5 Miata Base >> Repair and Diagnosis >> Engine Performance >> System >> On-Board Diagnostic [Engine Control System] >> DTC P0138 >> Diagnostic Procedure
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Diagnostic Procedure

DTC P0138 DIAGNOSTIC PROCEDURE TABLE

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 WDS or equivalent.
  • Is other DTC present?
 Yes Go to the appropriate DTC troubleshooting procedures.
(See DTC TABLE  .)
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 OBD-II FREEZE FRAME DATA  .
(See DTC TABLE  .)
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 VERIFY CURRENT INPUT SIGNAL STATUS 
  • Start engine.
  • Access O2S12 PID using WDS or equivalent.
  • Verify PID while racing engine at least 10 times  in PARK (AT) or NEUTRAL (MT).
  • Does PID stay above 0.55 V  ?
 Yes Replace sensor, then go to the next step.
(See REAR HEATED OXYGEN SENSOR (HO2S) REMOVAL/INSTALLATION .)
No Go to the next step.
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 WDS or equivalent.
  • Run the KOEO self-test with WDS or equivalent, or PCM adaptive memory procedure drive mode and HO2S heater, HO2S, and TWC repair verification drive mode.

    (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.
8 VERIFY AFTER REPAIR PROCEDURE  Yes Go to the applicable DTC troubleshooting.
(See DTC TABLE  .)
No Troubleshooting completed.
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