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2008 - MX-5 - Engine

DTC P0140 [LF]



DTC P0140

Rear HO2S no activity detected

DETECTION CONDITION

  • The PCM monitors the input voltage from the rear HO2S when the following conditions are met. Under the following monitoring conditions, if the input voltage from the rear HO2S does not even exceed 0.55 V though the short term fuel trim is controlled up to 20.5 % for 9.6 s, the PCM determines that sensor circuit is not activated.

    • MONITORING CONDITIONS
    • HO2S, HO2S heater and TWC repair verification drive mode

    • Following conditions are met for above 20.8 s

      • Engine speed is above 1,500 rpm.

      • Engine coolant temperature is above 70 °C {158 °F}.

    • Rear HO2S voltage is above 0.1 V

    Diagnostic support note
  • This is an intermittent 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 deterioration

  • Rear HO2S heater malfunction

  • Leakage exhaust system

  • Open circuit or short to ground in wiring harness between rear HO2S terminal A and PCM terminal 2Q

  • Insufficient compression

  • Engine 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 AND STORED DTC

NOTE:

  • If fuel monitor DTC, DTC P0132 is retrieved, ignore it until P0140 is fixed.

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

  • Verify pending and 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 P0140 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

Yes

Go to Step 8.

No

Go to the next step.

6

INSPECT INSTALLATION OF REAR HO2S
  • Check if rear HO2S is loosely installed.

  • Is sensor installed securely?

Yes

Go to the next step.

No

Install sensor securely, then go to Step 10.

7

INSPECT GAS LEAKAGE FROM EXHAUST SYSTEM
  • Visually check if any gas leakage is found between exhaust pipe and rear HO2S.

  • Is there any gas leakage?

Yes

Repair or replace any malfunctioning exhaust part, then go to Step 10.

No

  • Inspect the following wiring harnesses for open or short to ground circuit, repair or replace wiring harness if necessary.

    • Rear HO2S terminal A (wiring harness-side) to PCM terminal 2Q (wiring harness-side)

      • Repair or replace wiring harness if necessary.

  • If all items above are normal, replace malfunctioning sensor.

Then go to Step 10.

8

INSPECT SEALING OF ENGINE COOLANT PASSAGE

WARNING:

  • Removing the radiator cap when the radiator is hot is dangerous. Scalding coolant and steam may shoot out and cause serious injury.

  • When removing the radiator cap, wrap a thick cloth around and turn it slowly.

  • Remove radiator cap.

  • Perform procedure to bleed air from the engine coolant, then run the engine at idle.

  • Is there any small bubble, which makes the engine coolant white at filling opening?

    NOTE:

    • Large bubbles are normal since they are remaining air coming out from the engine coolant passage.

Yes

Air gets in from poor sealing on head gasket or other areas between combustion chamber and engine coolant passage.

Repair or replace the malfunctioning part, then go to Step 10.

No

Go to the next step.

9

INSPECT ENGINE COMPRESSION

Yes

Go to the next step.

No

Perform engine overhaul for repairs, then go to the next step.

10

VERIFY TROUBLESHOOTING OF DTC P0140 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.

  • Perform the KOER 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.

11

VERIFY AFTER REPAIR PROCEDURE

Yes

Go to the applicable DTC troubleshooting.

(See DTC TABLE [LF].)

No

Troubleshooting completed.




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