DFI ECM Tests W/Codes: Action:

ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE SOON" message on CCDIC panel. ECM uses 12 degrees for TPS value when ISC throttle switch closes. ECM uses RPM for all ISC calculations (will not use TPS reading for coast down throttle control).

The TPS is a 3-wire sensor receiving a 5-volt reference input from ECM over circuit No. 474, and a reference ground from ECM over circuit No. 476. The TPS sends a sensor output signal over circuit No. 417 to the ECM.

The sensor output signal is a DC voltage that varies with throttle angle, the TPS signal voltage is low (about .5 volts at minimum air setting). At high throttle angles, the TPS signal voltage is high (about 4.5 volts at wide open throttle).

Code EO21 is set when the ECM sees a high throttle angle (high TPS voltage) at low engine RPM. Code is designed to detect a TPS signal, over circuit No. 417, shorted to voltage.

NOTE: Test numbers refer to test numbers on diagnostic chart.

This step helps determine location of short to voltage. Short will be in TPS or circuit No. 417.
This step checks for an open ground in circuit No. 474. An open ground circuit will result in high TPS values whenever the TPS is plugged in.