Trouble CodesGM OBD Trouble CodesGM Code 21

CODE 21 - Throttle Position Sensor

Trouble Code 21 indicates that the Throttle Position Sensor (TPS) is reading abnormally high. TPS volts should be close to 0.42 V at closed throttle and rise smoothly in about 0.02 volt increments to a maximum reading of about 4.85 volts at WOT.

The conditions for setting this code are:

  • the engine is running, and
  • Code 33 or 34 (MAF error) is not set, and
  • TPS reading is > 4.90 volts
       - or -
  • TPS reading stays between 2.5 and 4.9 volts, and
  • MAF reading is < 15 grams/second, and
  • the above two conditions are present for more than 5 seconds

Note: During a Code 21 condition, the ECM uses a default TPS value of 2.6 volts. This will cause the engine to idle very high.

Typical causes for this code include:

1) Defective TPS
2) Short circuit in the TPS harness to +5 volt reference
3) Open sensor ground circuit
4) Defective ECM

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