P0139

DTC P0139: Secondary HO2S (Sensor 2) Slow Response

1. Reset the ECM/PCM.
2. Start the engine. Hold the engine at 3,000 rpm 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 with the scan tool or the HDS.

Does the voltage stay within 0.3 - 0.8 V for 2 minutes?

YES - Replace the secondary HO2S (Sensor 2).

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.