P0139 - HO2S 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 volt and 0.6 - 1 volt with the engine running at 2,000 rpm.