P0139

P0139 - O2 Sensor 1/2 Slow Response

For wiring diagrams, refer to.

• When Monitored: With the ECT more than 70 °C (158 °F), engine RPM between 1400 and 2300, vehicle speed between 64 and 96 km/h (40 and 60 MPH), and engine run time greater than 3 minutes.

• Set Condition: The PCM detects that the oxygen sensor signal does not switch from rich to lean adequately during monitoring. Two Trip Fault. Three good trips to turn off the MIL.

• Always perform the pre-diagnostic troubleshooting procedure before proceeding. Refer to => Non-DTC Based Diagnostics. Pre-Diagnostic Troubleshooting Procedure

Test Step 1 - Exhaust Leak

• A thorough exhaust leak test must be completed before removing an O2 sensor or any other part from the exhaust system. Do not remove any parts before an exhaust leak check has been completed.

• An exhaust leak may cause downstream fuel adaptives to reach limits, resulting in a false 1/2 oxygen sensor failure

• Perform the diagnostic procedure for checking the exhaust system for leaks. Refer to => Non-DTC Based Diagnostics

Were any problems found?

Yes

• Repair as necessary.

• Perform the PCM Verification Test. Refer to => Non-DTC
Based Diagnostics. PCM Verification Test

No

• Go to Test Step 2 => [ Test
Step 2 - DTC is Active ]

Test Step 2 - DTC is Active

• Check for contaminants that may have damaged the O2 sensor such as contaminated fuel, unapproved silicone, oil, or coolant.

• It may be necessary to test drive the vehicle within the DTC monitoring conditions in order for this DTC to set.

• Start the engine and allow it to reach operating temperature.

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 can result in personal injury or death.

• With a scan tool, select view DTCs.

Is the status active for this DTC?

Yes

• Go to Test Step 3 => [ Test
Step 3 - O2S 1/2 Signal Circuit Shorted to Voltage ]

No

• Refer to the checking for an intermittent DTC diagnostic procedure. Refer to => Non-DTC Based Diagnostics. Checking for an Intermittent DTC

Test Step 3 - O2S 1/2 Signal Circuit Shorted to Voltage

• Turn the ignition OFF.

• Disconnect the 1/2 oxygen sensor harness connector.

• Turn the ignition ON.

• Measure the voltage on the O2 1/2 signal circuit in the harness connector.

• Measure the voltage in reference to battery or chassis ground, not the O2S 1/2 return circuit.

Is the voltage more than 5.2 volts?

Yes

• Repair the circuit for a short to voltage.

• Perform the PCM Verification Test. Refer to => Non-DTC
Based Diagnostics. PCM Verification Test

No

• Go to Test Step 4 => [ Test
Step 4 - O2S 1/2 Return Circuit Shorted to Voltage ]

Test Step 4 - O2S 1/2 Return Circuit Shorted to Voltage

• Turn the ignition OFF.

• Disconnect the PCM harness connector.

• Turn the ignition ON.

• Measure the voltage on the O2 1/2 return circuit in the harness connector.

Is any voltage present?

Yes

• Repair the circuit for a short to voltage.

• Perform the PCM Verification Test. Refer to => Non-DTC
Based Diagnostics. PCM Verification Test

No

• Go to Test Step 5 => [ Test
Step 5 - O2S 1/2 Signal Circuit Shorted to Ground ]

Test Step 5 - O2S 1/2 Signal Circuit Shorted to Ground

• Turn the ignition OFF.

• Measure the resistance between ground and the O2 1/2 signal circuit in the harness connector.

Is the resistance less than 100 ohms?

Yes

• Repair the circuit for a short to ground.

• Perform the PCM Verification Test. Refer to => Non-DTC
Based Diagnostics. PCM Verification Test

No

• Go to Test Step 6 => [ Test
Step 6 - O2S 1/2 Return Circuit Shorted to Ground ]

Test Step 6 - O2S 1/2 Return Circuit Shorted to Ground

• Measure the resistance between ground and the O2S 1/2 return circuit in the harness connector.

Is the resistance less than 100 ohms?

Yes

• Repair the circuit for a short to ground.

• Perform the PCM Verification Test. Refer to => Non-DTC
Based Diagnostics. PCM Verification Test

No

• Go to Test Step 7 => [ Test
Step 7 - O2S 1/2 Signal Circuit Open or High Resistance ]

Test Step 7 - O2S 1/2 Signal Circuit Open or High Resistance

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 O2 1/2 return circuit between the harness connector and the appropriate terminal of special tool #8815.

Is the resistance less than 5.0 ohms?

Yes

• Go to Test Step 9 => [ Test
Step 9 - 1/2 Oxygen Sensor ]

No

• Repair the circuit for an open or high resistance.

• Perform the PCM Verification Test. Refer to => Non-DTC
Based Diagnostics. PCM Verification Test

Test Step 9 - 1/2 Oxygen Sensor

• Prior to replacing the O2 sensor, verify that the correct part number is being used in order to prevent improper O2S heater control.

• Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the 1/2 oxygen sensor and the PCM.

• Look for any chafed, pierced, pinched, or partially broken wires.

• Look for broken, bent, pushed out or corroded terminals. Verify that there is good pin to terminal contact in the related connectors.

• Refer to any technical service bulletins that may apply.

Were any problems found?

Yes

• Repair as necessary.

• Perform the PCM Verification Test. Refer to => Non-DTC
Based Diagnostics. PCM Verification Test

No

• Replace the 1/2 oxygen sensor.

• Perform the PCM Verification Test. Refer to => Non-DTC
Based Diagnostics. PCM Verification Test