|P0139 – O2 Circuit Slow Response (Bank 1, Sensor 2)|
|Description: The heated oxygen sensor (HO2S) monitor tracks the rate of voltage change during the rise and fall of the HO2S signal. When the rate of voltage change is less than a calibrated value, the powertrain control module (PCM) begins to modify the fuel trim attempting to increase the HO2S voltage switch rate. The DTC sets when the PCM is at the allowable limit or has exceeded an allowable length of time for fuel trim modification, without detecting an acceptable rate of voltage change.
Possible Causes: • Contaminated or damaged HO2S
• Deteriorating HO2S
• Exhaust leaks
• Aftermarket accessories
• Performance modifications
Diagnostic Aids: Access the HO2S test results from the Generic OBD-II menu to verify the DTC.