Operation CHARM: Car repair manuals for everyone.

DTC 21









Circuit Description:
The Throttle Position Sensor (TPS) is a variable resistor that signals the ECM the degree of throttle opening. The sensor is connected to a 5 volt reference and has the highest resistance at closed throttle. At wide open throttle the resistance is lowest and output to the ECM will be near 5 volts. When there is a Code 21, EPR is shut "OFF."
Code 21 means that the ECM has seen the following:
^ High voltage at ECM terminal "A2".
^ For a time in excess of 2 minutes.
^ Engine speed less than 1120 rpm.

Test Description:
Numbers below refer to the circled numbers on the diagnostic chart.
1. Confirms Code 21 and that fault is present.
2. Checks for 5 volt reference at TPS harness connector and separates an electrical circuit problem from a faulty TPS. If the circuit is OK, normal voltage reading will be about 5 volts.
3. Check to see if low reference voltage is due to an open wire or the ECM.