GM OBD Trouble Code 13

Oxygen sensor circuit open or no activity

The Oxygen Sensor monitors the oxygen content of the exhaust. By monitoring oxygen content, the Oxygen Sensor can tell the Engine Control Computer if too much or not enough fuel is being burned in the cylinders so the ECM can adjust the fuel mixture accordingly.

Fault Code Description

  • 13 - Oxygen sensor circuit open or no activity
  • On V-type engines with two O2 sensors, code 13 would indicate the left bank sensor


  • Engine running too rich (black smoke from exhaust) or too lean (lack of power)
  • The engine may run fine with no noticeable dirveability issues

Common Problems

  • A failed O2 sensor is the most common cause of a Code 13
  • A quick test for the O2 sensor circuit from the ECM would be to unplug the O2 sensor and check voltage from the harness side to ground. With the ignition on and the engine off, the reading should be around .5v.

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