Cadillac P1139: HO2S-12 (Bank 1 Sensor 2) Insufficient Switching

What Does The Cadillac P1139 Code Mean?

Engine started; test not completed this key cycle, Low Coolant Level “off”, and the PCM detected the number of rich-to-lean or lean-to-rich rear.

What Are The Potential Causes Of The Cadillac P1139 Code?

Below are some potential causes of this DTC:

• Fuel pressure is too high (i. e. , causing a rich air fuel mixture)
• HO2S may be contaminated (due to improper fuel or silicone)
• HO2S signal high or low reference circuit has high resistance
• PCM has failed

Recommended Parts

Below are some recommended auto parts to help you address the trouble code affecting your vehicle and get it running smoothly again:

>>> WORKPRO 582-piece Crimp Terminals, Wire Connectors, Heat Shrink Tube, Electrical Repair Kit
>>> A-Premium O2 Oxygen Sensor Upstream Downstream Replacement
>>> GM Genuine Parts 12633238 Engine Control Module

Note: During the purchasing process, please check carefully whether the part you want to buy fits your car!

Reference Sources

GM, 2013, Service Bullettin – Prior To Any Circuit Testing.