## DTC Troubleshooting: P0135 (41-2)

DTC P0135 (41-2): | Primary HO2S (Sensor 1) Heater Circuit Malfunction

1. | Reset the ECM/PCM.

2. | Start the engine. Is DTC P0135 indicated? YES - Go to 3. NO - Intermittent failure, system is OK at this time. Check for poor connections or loose terminals at the primary HO2S (Sensor 1) and at the ECM/ PCM.n

3. | Turn the ignition switch OFF.

4. | Disconnect the primary HO2S (Sensor 1) 4P connector.

5. | At the primary HO2S side, measure resistance between the primary HO2S (sensor 1) 4P connector terminals No. 3 and No. 4. Is there about 6 W (at room temperature)? YES - Go to 6. NO - Replace the primary HO2S (Sensor 1).n

6. | Check for continuity between body ground and the primary HO2S (Sensor 1) 4P connector terminals No. 3 and No. 4 individually. Is there continuity? YES - Replace the primary HO2S (Sensor 1).n NO - Go to 7.

7. | Turn the ignition switch ON (II).

8. | Measure voltage between the primary HO2S (Sensor 1) 4P connector terminal No. 3 and No. 4. Is there battery voltage? YES - Go to 9. NO - Go to 12.

9. | Turn the ignition switch OFF.

10. | Disconnect ECM/PCM connector A (31P).

11. | Check for continuity between ECM/PCM connector terminal A1 and body ground. Is there continuity? YES - Repair short in the wire between the ECM/PCM (A1) and the primary HO2S (Sensor 1).n NO - Update the ECM/PCM if it does not have the latest software, or substitute a known-good ECM/PCM, then recheck. If the symptom/indication goes away with a known-good ECM/PCM, replace the original ECM/ PCM.n

12. | Measure voltage between the primary HO2S (Sensor 1) 4P connector terminal No. 3 and body ground. Is there battery voltage? YES - Go to 13. NO - Check the No. 16 (7.5A) fuse in the under-dash fuse/relay box. If the fuse is OK, repair open in the wire between the primary HO2S (Sensor 1) and No. 16 (7.5A) fuse.n

13. | Turn the ignition switch OFF.

14. | Reconnect the primary HO2S (Sensor 1) 4P connector.

15. | Disconnect ECM/PCM connector A (31P).

16. | Turn the ignition switch ON (II).

17. | Measure voltage between ECM/PCM connector terminal A1 and A5. Is there 0.1 V or less? YES - Repair open in the wire between the ECM/PCM (A1) and the primary HO2S (Sensor 1).n NO - Update the ECM/PCM if it does not have the latest software, or substitute a known-good ECM/PCM, then recheck. If the symptom/indication goes away with a known-good ECM/PCM, replace the original ECM/ PCM.n