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2008 - MX-5 - Engine

DTC P0031 [LF]



DTC P0031

Front HO2S heater circuit low input

DETECTION CONDITION

  • The PCM monitors the front HO2S heater control voltage when the PCM turns the front HO2S heater on. If the control voltage is less than 50% of the battery voltage, the PCM determines that the front HO2S heater control circuit voltage is low.

    Diagnostic support note
  • This is a continuous monitor (HO2S heater).

  • 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

  • Front HO2S heater malfunction

  • Connector or terminal malfunction

  • Open circuit in wiring harness between ignition relay and front HO2S terminal C

  • Short to ground in wiring harness between ignition relay and front HO2S terminal C

  • Open circuit in wiring harness between front HO2S terminal D and PCM terminal 2BG

  • Short to ground in wiring harness between front HO2S terminal D and PCM terminal 2BG

  • 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 heater 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

INSPECT FRONT HO2S CONNECTOR FOR POOR CONNECTION
  • Turn the ignition switch off.

  • Disconnect the front HO2S connector.

  • Inspect for poor connection (such as damaged/pulled-out pins, and corrosion).

  • Is there any malfunction?

Yes

Repair or replace the terminal, then go to Step 9.

No

Go to the next step.

4

INSPECT FRONT HO2S HEATER POWER CIRCUIT FOR OPEN CIRCUIT OR SHORT TO GROUND
  • Turn the ignition switch to the ON position (Engine off).

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

  • Is the voltage B+?

Yes

Go to the next step.

No

Repair or replace the wiring harness for a possible open circuit or short to ground, then go to Step 9.

5

INSPECT FRONT HO2S HEATER CONTROL CIRCUIT FOR SHORT TO GROUND
  • Turn the ignition switch off.

  • Inspect for continuity between front HO2S terminal D (wiring harness-side) and body ground.

  • Is there continuity?

Yes

Repair or replace the wiring harness for a possible short to ground, then go to Step 9.

No

Go to the next step.

6

INSPECT FRONT HO2S HEATER CONTROL CIRCUIT FOR OPEN CIRCUIT
  • Turn the ignition switch off.

  • Inspect for continuity between front HO2S terminal D (wiring harness-side) and PCM terminal 2BG (wiring harness-side).

  • Is there continuity?

Yes

Go to the next step.

No

Repair or replace the wiring harness for a possible open circuit, then go to Step 9.

7

INSPECT PCM CONNECTOR FOR POOR CONNECTION
  • Turn the ignition switch off.

  • Disconnect the PCM connector.

  • Inspect for poor connection (such as damaged/pulled-out pins, and corrosion).

  • Is there any malfunction?

Yes

Repair or replace the terminal, then go to Step 9.

No

Go to the next step.

8

INSPECT FRONT HO2S HEATER

Yes

Replace the front HO2S, then go tothe next step.

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

No

Go to the next step.

9

VERIFY TROUBLESHOOTING OF DTC P0031 COMPLETED
  • Make sure to reconnect all disconnected connectors.

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

  • Perform the KOEO self-test (using M-MDS) or the HO2S heater, HO2S, and TWC Repair Verification Drive Mode (not using M-MDS).

    (See KOEO/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.

10

VERIFY AFTER REPAIR PROCEDURE

Yes

Go to the applicable DTC inspection.

(See DTC TABLE [LF].)

No

DTC troubleshooting completed.




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