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GM OBD Trouble Code 63

By Jim Taddei, May 1, 2009

Right bank O2 sensor circuit error

MAP sensor circuit signal voltage high (low vacuum indicated)

  • Depending on the model, code 63 can refer to two different systems.
  • Please choose from one of the above links for specific information on each system.

Right bank O2 sensor circuit error

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. On V-type engines with two O2 sensors, code 63 would indicate the right bank sensor.

Fault Code Description

  • 63 - Oxygen sensor circuit open or no activity

Symptoms

  • 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 63
  • 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.

MAP sensor circuit signal voltage high (low vacuum indicated)

The ECM uses the Manifold Absolute Pressure (MAP) sensor as an indication of engine load. High voltage would indicate low engine vacuum and higher engine load. Low voltage would indicate high engine vacuum and lower engine load. The ECM uses the information from this sensor to help calculate fuel delivery and spark timing.

Fault Code Description

  • 63 - MAP sensor circuit error (signal high indicating low vacuum)

Symptoms

  • Poor engine performance
  • Engine running rich (too much fuel, black smoke from exhaust)

Common Problems

  • GM MAP sensors do not commonly fail
  • Due to erratic engine vacuum, other engine performance problems can cause a code 63 to set

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