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Code 21: TPS Open Or MISADJUSTED

Code 21 means that the ECM has seen a high TPS voltage for more than about 10 seconds, below a specified RPM or below a specified engine load. Due to the pull-up resistor between terminals "21" and "2" within the ECM, an open in the TPS circuit will place about 5 volts (high TPS signal) at terminal "2" of ECM.

  1. This test checks the circuits from the TPS connector back to the ECM. Both wires should read about 5 volts due to the pull-up resistor in the ECM.
    NOTE: A 10-megohm resistance meter must be used. A lower resistance voltmeter would read virtually zero at terminal "B."
  2. This test checks if low voltage at TPS connector is an open in the circuit or a faulty ECM. A normal reading at the ECM is about 5 volts.
  3. This test simulates closed throttle. Dwell should increase if the ECM is good.
  4. This tests the resistance of the TPS switch. Normal reading is less than 20,000 ohms.
Fig 1: Code 21: TPS Open Or Misadjusted
G11191
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