OBD-II Trouble Code Description for P0139 GMC

O2 Sensor Circuit Slow Response

What does this mean?

OBD2 Code P0139 GM definition:
This involves the rear oxygen sensor on the driver’s side. This code indicates the engine air fuel ratio is not being adjusted by the oxygen sensor signal or the ECM as expected to do so, or not adjusted as often as expected to do so once the engine is warmed or under normal engine use.

Symptoms

Possible sumptoms of OBD code P0139 GM
You will likely not notice any drivability problems, although there may be symptoms.

Causes

Possible causes of OBD code P0139 GM
A code P0139 GM may mean that one or more of the following has happened: The oxygen sensor is faulty The wiring to the sensor is broken / frayed There is an exhaust leak

Possible Solutions

The simplest thing to do is to reset the code and see if it comes back. If the code comes back, the problem is more than likely the rear driver’s side oxygen sensor. You will likely wind up replacing it but you should also consider these possible solutions: Check and fix any exhaust leaks Check for wiring problems (shorted, frayed wires) Check the frequency and amplitude of the oxygen sensor (advanced) Check for a deteriorating / contaminated oxygen sensor, replace if necessary Check for inlet air leaks Check the MAF sensor for proper operation