Code 21 - TPS Circuit High

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 terms. "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 Circuit High