DTC Troubleshooting

DTC Troubleshooting: P0139

DTC P0139: Secondary HO2S (Sensor 2) Slow Response

NOTE: Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information. Initial Inspection and Diagnostic Overview

1. Turn the ignition switch to ON (II).

2. Clear the DTC with the HDS.

3. Start the engine. Hold the engine speed at 3,000 rpm without load (in neutral) until the radiator fan comes on, then let it idle.

4. Test-drive under these conditions:
- Engine coolant temperature (ECT SENSOR 1) above 158 °F (70 °C)

- Transmission in 4th

- Vehicle speed at 35 mph (56 km/h) or more

- Drive about 15 seconds

5. Monitor the OBD STATUS for DTC P0139 in the DTCs MENU with the HDS.

Does the screen indicate FAILED?
YES - Go to step 6.

NO - If the screen indicates PASSED, intermittent failure, the system is OK at this time. Check for poor connections or loose terminals at the secondary HO2S (Sensor 2) and the ECM. If the screen indicates EXECUTING, keep driving until a result comes on. If the screen indicates OUT OF CONDITION, go to step 3 and recheck.


6. Turn the ignition switch to LOCK (0).

7. Replace the secondary HO2S (Sensor 2). Secondary HO2S Replacement

8. Turn the ignition switch to ON (II).

9. Reset the ECM with the HDS.

10. Do the ECM idle learn procedure. ECM Idle Learn Procedure

11. Start the engine, and let it idle without load (in neutral) until the radiator fan comes on.

12. Test-drive under these conditions:
- Engine coolant temperature (ECT SENSOR 1) above 158 °F (70 °C)

- Transmission in 4th

- Vehicle speed at 35 mph (56 km/h) or more

- Drive about 15 seconds

13. Check for Temporary DTCs or DTCs with the HDS.

Is DTC P0139 indicated?
YES - Check for poor connections or loose terminals at the secondary HO2S (Sensor 2) and the ECM, then go to step 1.

NO - Go to step 14.


14. Monitor the OBD STATUS for DTC P0139 in the DTCs MENU with the HDS.

Does the screen indicate PASSED?
YES - Troubleshooting is complete. If any other Temporary DTCs or DTCs were indicated in step 13, go to the indicated DTC's troubleshooting.

NO - If the screen indicates FAILED, check for poor connections or loose terminals at the secondary HO2S (Sensor 2) and the ECM, then go to step 1. If the screen indicates EXECUTING, keep driving until a result comes on. If the screen indicates OUT OF CONDITION, go to step 11.