P0138
P0138-O2 SENSOR 1/2 CIRCUIT HIGH
For a complete wiring diagram, refer to the Wiring Information.
Theory of Operation
The Oxygen Sensors (O2 Sensor) are used for fuel control and catalyst monitoring. Each O2 Sensor measures the oxygen content of the exhaust stream. When the engine is started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the O2 Sensor signal voltage while calculating the air-to-fuel ratio. The heating elements inside each O2 Sensor heats the sensor to bring it to operating conditions faster. This allows the system to enter Closed Loop earlier and the PCM to calculate the air-to-fuel ratio sooner. While the engine runs, the O2 Sensor heats up and begins to generate a voltage within a range of 0-1,275 mV. Once sufficient O2 Sensor voltage fluctuation is observed by the PCM, Closed Loop is entered. The PCM uses the O2 Sensor voltage to determine the air-to-fuel ratio. An O2 Sensor voltage that increases toward 1,000 mV indicates a rich fuel mixture. An O2 Sensor voltage that decreases toward 0 mV indicates a lean fuel mixture. The Powertrain Control Module (PCM) makes short term and long term fuel corrections to maintain stoichiometric fuel/air ratio for best catalytic converter efficiency. Short term fuel correction is based on upstream O2 Sensor output and is designed for quick engine response. The long term fuel correction compensated for variations in the engine specifications, sensor tolerances and component aging and is designed to correct rich and lean conditions over a longer period of time.
- When Monitored:
Continuously with the engine running and the O2 Sensor in closed loop mode.
- Set Condition:
The Powertrain Control Module (PCM) detects a voltage greater than 5.0 volts on the signal or reference ground circuits. The DTC will set as Pending after one trip and Active after two trips. Three good trips to turn off the MIL.
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.
Diagnostic Test
1. ACTIVE DIAGNOSTIC TROUBLE CODE (DTC)
1. Start the engine and allow it to idle for at least 60 seconds. Allow the engine to run long enough for the O2 Sensor to enter closed loop operation.
WARNING:
When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing. Failure to follow these instructions may result in possible serious or fatal injury.
2. With the scan tool, read the active DTCs.
Is the DTC Active at this time?
Yes
- Go To 2
No
- Perform the INTERMITTENT CONDITION diagnostic procedure. Intermittent Condition Test.
2. (K141) O2 SENSOR 1/2 SIGNAL CIRCUIT SHORTED TO VOLTAGE
1. Turn the ignition off.
2. Disconnect the O2 Sensor 1/2 harness connector.
3. Turn the ignition on.
4. Measure the voltage on the (K141) O2 Sensor 1/2 Signal circuit at the O2 Sensor 1/2 harness connector.
NOTE: Measure the voltage in reference to ground, not the (K904) O2 Sensor Return circuit.
Is the voltage reading above 5.0 volts?
Yes
- Repair the short to voltage in the (K141) O2 Sensor 1/2 Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 3
3. (K904) O2 SENSOR RETURN CIRCUIT SHORTED TO VOLTAGE
1. Measure the voltage on the (K904)O2 Sensor Return circuit at the O2 Sensor harness connector.
Is the voltage reading above 5.0 volts?
Yes
- Repair the short to voltage in the O2 Return Downstream circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 4
4. O2 SENSOR
1. With the scan tool, monitor the O2 Sensor 1/2 voltage.
2. Connect a jumper between the (K141) O2 Sensor 1/2 Signal circuit and the (K904) O2 Sensor Return circuit at the O2 Sensor 1/2 harness connector.
Is the voltage between 2.3 and 2.7 Volts with the jumper in place?
Yes
- Verify that there is good pin to terminal contact in the O2 Sensor1/2 and Powertrain Control Module connectors. If OK, replace the O2 Sensor. .
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 5
NOTE: Remove the jumper wire before continuing.
5. (K141) O2 SENSOR 1/2 SIGNAL CIRCUIT OPEN/HIGH RESISTANCE
1. Turn the ignition off.
2. Disconnect the PCM C1 harness connector.
3. Measure the resistance of the (K141) O2 Sensor 1/2 Signal circuit between the O2 Sensor 1/2 harness connector and the PCM C1 harness connector.
Is the resistance below 5.0 Ohms?
Yes
- Go To 6
No
- Repair the O2 Sensor 1/2 Signal circuit for an open or high resistance.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
6. O2 RETURN DOWNSTREAM CIRCUIT OPEN/HIGH RESISTANCE
1. Measure the resistance of the (K904) O2 Sensor Return circuit between the O2 Sensor 1/2 harness connector and the PCM C1 harness connector.
Is the resistance below 5.0 Ohms?
Yes
- Go To 7
No
- Repair the (K904) O2 Sensor Return circuit for an open or high resistance.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
7. POWERTRAIN CONTROL MODULE (PCM)
1. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the Oxygen Sensor 1/2 and the Powertrain Control Module (PCM).
2. Look for any chafed, pierced, pinched or partially broken wires.
3. Look for broken, bent, pushed out or corroded terminals. Verify that there is good pin to terminal contact in the O2 Sensor and Powertrain Control Module harness connectors.
4. Perform any Technical Service Bulletins that may apply.
Were there any problems found?
Yes
- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Replace and program the Powertrain Control Module. .
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.