Trouble CodesGM OBD Trouble CodesGM Code 33

CODE 33 - MAP Sensor or MAF Sensor depending on the enigne

Trouble Code 33 indicates that the Mass Air Flow (MAF) sensor is reporting more air is entering the engine than makes sense based on RPM and TPS. The MAF sensor produces a frequency output; around 30 Hz at idle to 150 Hz under acceleration. The frequency varies proportionally to airflow. The ECM monitors the frequency and thus determines airflow into the engine. Typical idle MAF is 5 to 7 grams per second.

The conditions for setting this code are:

  • no Code 21 or 22 (TPS Error) present, and
  • the air flow reported is > 40 grams per second, and
  • TPS indicates < 10% throttle position, and
  • the engine speed is 1400 RPM or less, and
  • the above conditions exist for over 5 seconds.

Typical causes for this code include:

1) Faulty MAF-to-ECM connection
2) Exceedingly noisy spark plug wires
3) Poor routing of MAF harness (i.e. near coil packs)
4) Maladjusted TPS sensor
5) Defective MAF sensor
6) Defective ECM

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