Code 21

CIRCUIT DESCRIPTION
The throttle position sensor (TPS) provides a voltage signal that changes relative to the throttle plate. Signal voltage will vary from about 0.5 volts at idle to about 5 volts at wide open throttle. The Engine Control Module (ECM) also receives this signal.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.
1. This test checks for short to voltage at terminal 6 of the TCM. Wires may be shorted together at TPS connector.
2. A faulty ground circuit will cause Trouble Code 21 to set.
3. To isolate a short, remove the control units one at a time while measuring voltage.

DIAGNOSTIC AIDS
Trouble Code 21 sets when the TCM detects greater than 4.9 volts at terminal 6. In the event of an electrical failure, both 1-2/3-4 and 2-3 shift solenoids are de-energized. The transmission will drive in backup mode.

CIRCUIT DIAGRAM

Throttle Position Sensor Circuit:

CODE 21 DIAGNOSTIC CHART

Code 21 Diagnostic Chart: