P0139 - O2 Sensor Circuit Slow Response (Bank 1, Sensor 2)

The HO2S-12 circuit is monitored by the Powertrain Control Module (PCM). The test fails when it takes more than the specified time for the HO2S-12 to respond between rich and lean conditions.

Possible Causes:
- HO2S-12 circuit is open
- HO2S-12 circuit is shorted to VPWR
- HO2S-12 circuit is shorted to GND
- Rear HO2S
- Fuel pressure
- Injectors
- Intake air leaks

Diagnostic Aids:
The O2S-12 PID should vary between 0-0.3 Volts and 0.6-1 Volts with the engine running at 2000 rpm.