DTC 21

Fig. 68 - Chart #21 Diagnosis:

Code 21 means that the ECM has seen a high TPS voltage for:
a. Over about 10 seconds
b. Below as specified RPM
c. 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 Term. "2" of the ECM.



1. Checks the circuits from the TPS connector back to the ECM. Both wires should read about 5V because of the pull-up resistor in the ECM. A 10 Meg. ohm resistance meter must be used. A lower resistence voltmeter would read virtually zero at terminal B.
2. Checks to see if the low voltage at the TPS connector is an open in open in the circuit or a faulty ECM. A normal reading at the ECM is about 5V.
3. This step simulates closed throttle, so dwell should increase if the ECM is good.
4. This step tests the resistance of the TPS switch itself. A normal reading is under 20,000 ohms.