Jump to content
CaddyInfo Cadillac Forum

O2 Sensors


Recommended Posts

The incompetance at my local Cadillac dealer is amazing. Anyway, with a pcm code of 1139 which indicates a bad O2 sensor I am wondering which sensor this is first of all. I have found a sensor right between the radiator and the engine, then one under the car in front of the cat convertor, and one ofter the convertor. My question is, are all of these sensors the same except for the connectors. And why the heck does GM put different connectors on these O2 sensors? I would like to swap a couple sensors and see if I get a different code to verify the sensor is actually bad. Thanks for the help.

Link to comment
Share on other sites

P1139 - Heated Oxygen Sensor (HO2S) Insuff. Switching Bank 1 Sensor 2

Bank 1 Sensor 1 = right bank manifold (firewall side)

Bank 1 Sensor 2 = pre-cat

Bank 1 Sensor 3 = aft-cat

Bank 2 Sensor 1 = left bank manifold (radiator side)

Different connectors would make me think they are different sensors. I think the pre-cat and aft-cat are heated. That may be the difference.

Link to comment
Share on other sites

From the ACDelco web catalog for a '97 model:

Manifold sensors are ACDelco #AFS125

Pre-cat and post-cat sensors are ACDelco #AFS98

Your DTC of P1139 is "Insuff. Switching Bank 1 Sensor 2", or the pre-cat in your case. Should be plug-compatible with the post-cat sensor.


Drive your car.

Use your cell phone.


Link to comment
Share on other sites

Just an update on my 97 STS. The pre-cat and aft-cat O2 sensors are interchangeable (Same plug connector). I easily changed the 2 sensors and now just have to wait for a check engine code to pop up and see if it is the same code or if it follows the sensor and gives me a different zone code. The O2 sensors take a 7/8" open end wrench to remove and come out easier than I expected. Thanks for the help so far guys.

Link to comment
Share on other sites


This topic is now archived and is closed to further replies.

  • Recently Browsing   0 members

    • No registered users viewing this page.
  • Create New...