GM OBD Trouble Code 33

By Jim Taddei, May 1, 2009

MAP Sensor Circuit Error (Signal High Indicating Low Vacuum)

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

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


  • 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 33 to set

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