P0138
P0138-O2 SENSOR 1/2 CIRCUIT HIGH
For a complete wiring diagram refer to: Electrical Diagrams
When Monitored
O2 Sensor Heater Temperature is greater than 496°C (925°F) and battery voltage greater than 10.99 volts.
Set Condition
The Oxygen Sensor voltage is above 3.7 volts for 30 seconds. One Trip Fault. Three good trips to turn off the MIL.
Possible Causes
- (K141) O2 1/2 SIGNAL CIRCUIT SHORTED TO BATTERY VOLTAGE
- (K904) O2 DOWNSTREAM RETURN CIRCUIT SHORTED TO BATTERY VOLTAGE
- (K141) O2 1/2 SENSOR SIGNAL CIRCUIT OPEN
- (K904) O2 DOWNSTREAM RETURN CIRCUIT OPEN
- O2 SENSOR
- PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.
Diagnostic Test
1. O2 SENSOR ABOVE 3.7 VOLTS
NOTE: When only one O2 Sensor is shorted to voltage, the scan tool will display all O2 Sensor voltage readings at approximately 5.0 volts. When diagnosing this DTC, only diagnose the O2 Sensor that set the DTC.
Start the engine.
Allow the engine to reach normal operating temperature.
With a scan tool, read the 1/2 O2 Sensor voltage.
Is the voltage above 3.7 volts?
Yes >> Go To 2
No >> Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
2. (K141) O2 1/2 SIGNAL CIRCUIT SHORTED TO BATTERY VOLTAGE
Start the engine and allow the engine to idle.
Disconnect the 1/2 O2 Sensor harness connector.
Measure the voltage on the (K141) O2 Sensor 1/2 Signal circuit in the O2 Sensor harness connector.
NOTE: Measure the voltage in reference to ground, not the (K904) O2 Downstream Return circuit.
Is the voltage above 5.2 volts?
Yes >> Repair the short to battery voltage in the (K141) O2 Sensor 1/2 Signal circuit.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
No >> Go To 3
3. (K904) O2 DOWNSTREAM RETURN CIRCUIT SHORTED TO BATTERY VOLTAGE
Turn the ignition off.
Disconnect the PCM harness connectors. Ignition on, engine not running.
Measure the voltage on the (K904) O2 Downstream Return circuit in the O2 Sensor harness connector.
Is there any voltage present?
Yes >> Repair the short to battery voltage in the (K904) O2 Downstream Return circuit.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
No >> Go To 4
4. O2 SENSOR
Turn the ignition off.
Connect the PCM harness connectors.
Connect a jumper wire between the (K141) O2 1/2 Signal circuit and the (K904) O2 Downstream Return circuit in the 1/2 O2 Sensor harness connector.
Ignition on, engine not running.
With a scan tool, monitor the 1/2 O2 Sensor voltage.
Is the voltage between 2.3 and 2.7 volts with the jumper wire installed?
Yes >> Replace the O2 Sensor.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
No >> Go To 5
NOTE: Remove the jumper wire before continuing.
5. (K141) O2 1/2 SIGNAL CIRCUIT OPEN
Turn the ignition off.
CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform diagnosis.
Measure the resistance of the (K141) O2 1/2 Signal circuit from the O2 Sensor harness connector to the appropriate terminal of special tool #8815.
Is the resistance below 5.0 ohms?
Yes >> Go To 6
No >> Repair the open in the (K141) O2 1/2 Signal circuit.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
6. (K904) O2 DOWNSTREAM RETURN CIRCUIT OPEN
Measure the resistance of the (K904) O2 Downstream Return circuit from the O2 Sensor harness connector to the appropriate terminal of special tool #8815.
Is the resistance below 5.0 ohms?
Yes >> Go To 7
No >> Repair the open in the (K904) O2 Downstream Return circuit.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
7. PCM
NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.
Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.
Were there any problems found?
Yes >> Repair as necessary
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
No >> Replace and program the Powertrain Control Module per Service Information.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test