## 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 scan tool. Does the voltage stay within 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 wires at the secondary HO2S (Sensor 2) and at the ECM/ PCM.n