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 (A/T in P or N, M/T 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/PCM.

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/PCM (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/PCM ECM/PCM Update if it does not have the latest software, or substitute a known-good ECM/PCM Service and Repair, then do the repair verification.
-NO- Repair an open in the SO2 wire between the ECM/PCM (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/PCM with the HDS How To Troubleshoot The Fuel And Emissions Systems.

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

-5. Start the engine, and let it idle without load (A/T in P or N, M/T 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 D
* 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/PCM was substituted, replace the original ECM/PCM Service and Repair. If any other Pending or Confirmed DTCs were indicated, go to the indicated DTC's troubleshooting.
-FAILED- Go to step 1 and recheck. If the ECM/PCM was updated, substitute a known-good ECM/PCM 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.