P0139

DTC P0139: Secondary HO2S (Sensor 2) Slow Response

1. Reset the ECM.
2. Start the engine. Hold the engine at 3,000 rpm without load (in neutral) until the radiator fan comes on.
3. Check the secondary HO2S (Sensor 2) output voltage at 3,000 rpm with the HDS or a scan tool.

Is there 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.