DTC Troubleshooting

Control System DTCs

DTC Troubleshooting: P0138

DTC P0138 : Secondary HO2S (Sensor 2) Circuit High Voltage

NOTE: Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information How To Troubleshoot The Fuel And Emissions Systems.

1. Problem verification:

Problem verification
-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.

-4. Check the HO2S S2 OUTPUT VOLTAGE in the DATA LIST with the HDS.

Does the voltage stay at 1.27 V or more?
-YES- The failure is duplicated. Go to step 2.
-NO- Intermittent failure, the system is OK at this time. Check for poor connections or loose terminals at secondary HO2S (Sensor 2) and the ECM.

2. Determine possible failure area (Secondary HO2S (Sensor 2), others):

Determine possible failure area (Secondary HO2S (Sensor 2), others)
-1. Turn the ignition switch to LOCK (0).

-2. Disconnect the following connector.





-3. Connect terminals A and B with a jumper wire.









-4. Turn the ignition switch to ON (II).

-5. Check the HO2S S2 OUTPUT VOLTAGE in the DATA LIST with the HDS.

Does the voltage stay at 1.27 V or more?
-YES- Go to step 3.
-NO- Replace secondary HO2S (Sensor 2) Secondary HO2S Removal and Installation, then do the repair verification.

3. Open wire check (SO2_SG line):

Open wire check (SO2_SG line)
-1. Turn the ignition switch to LOCK (0).

-2. Remove the jumper wire from the secondary HO2S (Sensor 2) 4P connector.

-3. Connect terminals A and B with a jumper wire.









-4. Turn the ignition switch to ON (II).

-5. Check the HO2S S2 OUTPUT VOLTAGE in the DATA LIST with the HDS.

Does the voltage stay at 1.27 V or more?
-YES- The SO2_SG wire is OK. Go to step 4.
-NO- Repair an open in the SO2_SG wire between the ECM (C47) and secondary HO2S (Sensor 2), then do the repair verification.

4. Open wire check (SO2 line):

Open wire check (SO2 line)
-1. Turn the ignition switch to LOCK (0).

-2. Jump the SCS line with the HDS.

-3. Disconnect the following connector.





-4. Check for continuity between test points 1 and 2.









Is there continuity?
-YES- The SO2 wire is OK. Update the ECM ECM/PCM Update if it does not have the latest software, or substitute a known-good ECM Service and Repair, then do the repair verification.
-NO- Repair an open in the SO2 wire between the ECM (B46) and secondary HO2S (Sensor 2), then do the repair verification.

Repair verification (OBD STATUS check):

-1. Reconnect all connectors.

-2. Turn the ignition switch to ON (II).

-3. Reset the ECM with the HDS How To Troubleshoot The Fuel And Emissions Systems.

-4. Do the ECM idle learn procedure ECM/PCM Idle Learn Procedure.

-5. Start the engine, and let it idle without load (in neutral) until the radiator fan comes on.

-6. Test-drive under these conditions:
* Engine coolant temperature (ECT SENSOR 1) above 158 °F (70 °C)
* Transmission in 3rd or 4th
* Engine speed between 1,500-3,000 rpm
* Drive 1 minute or more

-7. Monitor the OBD STATUS for DTC P0138 in the DTCs MENU with the HDS.

Does the HDS indicate PASSED, FAILED, EXECUTING, or OUT OF CONDITION?
-PASSED- Troubleshooting is complete. If the ECM was substituted, replace the original ECM Service and Repair. If any other Pending or Confirmed DTCs are indicated, go to the indicated DTC's troubleshooting.
-FAILED- Go to step 1 and recheck. If the ECM was updated, substitute a known-good ECM Service and Repair, then check the OBD STATUS again.
-EXECUTING- Keep the test condition until a result comes on.
-OUT OF CONDITION- Meet the test condition, and check the OBD STATUS again.