E021

TEST CONDITIONS
1. RPM between 25 and 3000.

FAILURE CONDITIONS:
TPS value equal to or greater than 72 degrees for 0.7 seconds.

ACTION TAKEN
1. ECM turns on "Engine Control System Fault" telltale;
2. ECM commands BCM to display "Service Soon" message on the Driver Information Center (DIC);
3. ECM disables the Viscous Converter Clutch;
4. ECM sets TPS equal to 13 degrees when the Throttle Switch is open and 6 degrees when the Throttle Switch is closed.

DESCRIPTION
The Throttle Position Sensor (TPS) is a "3-wire" sensor or potentiometer. A 5 volt reference is provided at Pin C on CKT 474 and ground is provided at Pin B on CKT 1076. The TPS signal circuit (Pin A CKT 417) varies between ground and 5 volts based on the position of the throttle plates. At low throttle angle, the TPS signal voltage is low (about 5 volts at minimum air setting) and at high throttle angles, the TPS signal voltage is high (about 4.5 volts at WOT). The ECM uses TPS information to determine fueling needs (WOT enrichment, deceleration enleanment, acceleration enrichment).

Code EO21 is set when the ECM receives a high TPS voltage (high throttle angle) at low engine RPM. Possible causes of Code EO21 are:
1. TPS signal (CKT 417) shorted to voltage;
2. TPS ground (CKT 1076) open.

Notes on Fault Tree
1. Checking for shorted TPS or shorted wiring. If the data value stays greater than -7 with the TPS disconnected, the problem is in the wiring.
2. Checking for an open in CKT 1076 between the TPS and ECM. An open in CKT 1076 will cause the TPS signal to always be high whenever the TPS is plugged in.

Notes on Intermittents
If Code EO21 is stored as history, manipulate the TPS connector, TPS wiring, and ECM connector while observing ECM Data ED01. Check the TPS and the TPS test point connector for shorts to voltage. Cycle the TPS through its travel and tap on the TPS with a pencil or pocket screwdriver to test for an intermittent TPS. If the fault is induced, ECM Data ED01 will momentarily skip to 72 degrees or greater. If wiring and connectors check out OK, substitute a known good TPS and retest.