Action Taken

WARNING: This page is about a different car, the 1990 Cadillac Fleetwood and 1990 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.

ECM turns on SERVICE SOON light.
ECM disables VCC.
ECM uses 13 degrees for TPS value with ISC throttle switch open at 6 degrees for TPS value when ISC throttle switch closes.

The TPS is a 3-wire sensor or potentiometer with a 5-volt reference input from ECM to sensor circuit No. 474. This is a reference ground from ECM to sensor circuit No. 476 and a sensor output signal circuit No. 417 from sensor to ECM. The sensor output signal is a DC voltage that varies with throttle angle. At low throttle angle, the TPS signal voltage is low (about .5 volt at minimum air setting) and at high throttle angles. The TPS signal voltage is high at about 4.5 volts at wide open throttle.

Code E21 is set when ECM sees a high throttle angle (high TPS voltage) at low engine RPM. The code is designed to detect a TPS signal (circuit No. 417) shorted to voltage.

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

Test Number 1) Check for shorted TPS or shorted wiring. If data value stays greater than -7 with TPS disconnected, problem is in wiring.

Test Number 2) Check for an open circuit No. 476 between TPS and ECM. An open circuit will result in high TPS values whenever TPS is plugged in.