DTC Troubleshooting: P0139 (63-3)

DTC P0139 (63-3):  Secondary HO2S (Sensor 2) Slow Response

1.Reset the ECM/PCM.

2.Start the engine. Hold the engine at 3,000 rpm (min-1) with no load (in Park or neutral) until the radiator fan comes on.

3.Check the secondary HO2S (Sensor 2) output voltage at 3,000 rpm (min-1) with the HDS or the scan tool.

Is there 0.3-0.8 V for 2 minutes?


YES - Replace the  secondary HO2S (Sensor 2).n


NO - Intermittent failure, system is OK at this time. Check for poor connections or loose terminals at the secondary HO2S (Sensor 2) and at the ECM/ PCM.n