DTC P0138[AJ (3.0L Duratec)]

id0102a4805100

DTC P0138

Rear HO2S (RH) sensor circuit out of range high voltage
DETECTION CONDITION
•  The PCM monitors the rear HO2S (RH) voltage at the PCM terminal 35. If during testing the PCM detects that the rear HO2S (RH) is greater than 1.5 V, the PCM determines the rear HO2S (RH) circuit is out of range high voltage.
POSSIBLE CAUSE
•  Rear HO2S (RH) signal circuit shorted to front HO2S (RH) heater power inside of the rear HO2S (RH).
•  Rear HO2S (RH) signal circuit shorted to VPWR or VREF in harness.
•  PCM malfunction.

Diagnostic procedure

STEP

INSPECTION

ACTION
1
VERIFY FREEZE FRAME DATA HAS BEEN RECORDED
•  Has FREEZE FRAME DATA been recorded?
Yes
Go to the next step.
No
Record the FREEZE FRAME DATA on the repair order, then go to the next step.
2
VERIFY SERVICE INFORMATION AVAILABILITY
•  Verify related Service Information availability.
•  Is any related Service Information available?
Yes
Perform repair or diagnosis according to the available Service Information.
If the vehicle is not repaired, go to the next step.
No
Go to the next step.
3
IDENTIFY TRIGGER DTC FOR FREEZE FRAME DATA
•  Is DTC P0138 on the FREEZE FRAME DATA?
Yes
Go to the next step.
No
Go to the FREEZE FRAME DATA DTC inspection.
(See DTC TABLE[AJ (3.0L Duratec)].)
4
CHECK REAR HO2S (RH) SIGNAL LEVEL TOO HIGH
Note
•  Fuel calculations can be affected by abnormal air leaks.
•  Carefully inspect the following areas for potential air leaks:
―  Hoses connecting to MAF/IAT sensor assembly.
―  Hoses connecting to throttle body.
―  Intake manifold gasket leaks.
―  PCV disconnected.
―  The vacuum lines are disconnected.
―  Improperly seated engine oil dipstick, tube or oil fill cap.
―  Exhaust gas leaks at flanges and gaskets.
•  Raise the vehicle on a hoist and make sure the vehicle is level.
•  Visually inspect for the following:
―  Exhaust leaks at flanges and gaskets.
―  Rear HO2S (RH) not torqued to specification.
―  Physical exhaust system concerns.
―  Aftermarket exhaust.
―  Punctures or cracks in the catalyst.
•  Where any of the above conditions or concerns found during inspection?
Yes
Repair or replace malfunctioning part, then go to Step 10.
No
Go to the next step.
5
CHECK FOR REAR HO2S (RH) CIRCUIT FOR SHORT TO GROUND IN HARNESS
•  Disconnect the PCM and rear HO2S (RH) connectors.
•  Measure the resistance between the following the PCM terminals at the harness side connector
―  Between 35 and battery negative post
―  Between 35 and 91, 95
•  Is the resistance above 10,000 ohms?
Yes
Go to the next step.
No
Repair short circuit, then go to Step 10.
6
CHECK REAR HO2S (RH) CIRCUIT FOR OPEN IN HARNESS
•  Measure the resistance between the following at the harness side connector.
―  Between the PCM terminal 95 and rear HO2S (RH) terminal A
―  Between the main relay and rear HO2S (RH) terminal C
―  Between the PCM terminal 35 and rear HO2S (RH) terminal B
―  Between the PCM terminal 91 and rear HO2S (RH) terminal D
•  Is the resistances below 5.0 ohms?
Yes
Go to the next step.
No
Repair open circuit, then go to Step 10.
7
CHECK REAR HO2S (RH) CIRCUIT VOLTAGE
•  Connect the PCM and rear HO2S (RH) connectors.
•  Start the engine.
•  Access the O2S12 PID using the M-MDS
•  Is the O2S12 PID greater than 1.5 V?
Yes
Go to Step 9.
No
Go to the next step.
8
CHECK FRONT HO2S (RH) CIRCUIT VOLTAGE
•  Disconnect the front HO2S (RH) connector.
•  Place a jumper wire between terminal C and B at the front HO2S (RH) harness side connector.
•  Start the engine.
•  Access the O2S12 PID using the M-MDS
•  Is the O2S12 PID greater than 1.5 V?
Yes
Replace the rear HO2S (RH), then go to Step 10.
No
Intermittent concerns exist, then go to Step 10.
9
CHECK FOR OVER VOLTAGE IN THE PCM
•  Start the engine.
•  Disconnect the rear HO2S (RH) connector.
•  Measure the voltage between the following terminals at the harness side connector.
―  Between rear HO2S (RH) terminal B and battery negative post.
―  Between rear HO2S (RH) terminal D and battery negative post.
•  Is the voltage below 1.5 V?
Yes
Replace the rear HO2S (RH), then go to the next step.
No
Intermittent concerns exist, then go to the next step.
10
VERIFY TROUBLESHOOTING OF DTC P0138 COMPLETED
•  Make sure to reconnect all disconnected connectors.
•  Clear the DTC from the PCM memory using the M-MDS.
•  Drive the vehicle at 64 km/h {40 MPH} for at least 5 minutes.
•  Is the PENDING CODE same DTC present?
Yes
Replace the PCM, then go to the next step.
(See PCM REMOVAL/INSTALLATION[AJ (3.0L Duratec)].)
No
Go to the next step.
11
VERIFY AFTER REPAIR PROCEDURE
•  Perform “AFTER REPAIR PROCEDURE”.
•  Is there any DTC present?
Yes
Go to the applicable DTC inspection.
(See DTC TABLE[AJ (3.0L Duratec)].)
No
Troubleshooting completed.