Powertrain Controls - ECM/PCM

Diagnostic Trouble Code (DTC) 21:

Throttle Position Sensor Circuit:

CIRCUIT DESCRIPTION
The Throttle Position (TP) sensor provides a voltage signal that changes, as throttle blade opens or closes. Signal voltage should vary from about 0.6 volt at idle to about 5 volts at Wide Open Throttle (WOT).

The TP sensor signal is one of the most important inputs used by the Powertrain Control Module (PCM) for fuel control and for most of the PCM controlled outputs.

DIAGNOSTIC TROUBLE CODE (DTC) 21 WILL SET WHEN
TP sensor signal is greater than 2.5 volts, engine idling (less than 10 grams per second of air flow), all conditions met for 5 seconds or TP sensor signal voltage over 4.8 volts with ignition "ON."

ACTION TAKEN (PCM DEFAULT)
The Malfunction Indicator Lamp (MIL) will illuminate, transmission Torque Converter Clutch (TCC) will not apply, high transmission line pressure, fixed shift points, hard shifts and no fourth gear in hot mode.

DTC CHART TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. With throttle closed, the TP sensor should display between 0.3 and 0.9 volt. If it does not, check throttle cable adjustment and Traction Control System (TCS) adjuster assembly operation.

2 With the TP sensor disconnected, the TP sensor voltage should go low, if the PCM and wiring are OK.

3. Probing CKT 452 with a test light to 12 volts checks the sensor ground. A faulty sensor ground will cause a DTC 21.

4. Refer to Brakes and Traction Control/Diagrams for detailed circuit description before replacing any components.

5. It the TP sensor or throttle body is replaced, the Electronic Brake and Traction Control Module (EBTCM) must "learn" the TP sensor idle position voltage with the new components installed. This is necessary to ensure effective engine torque reduction during TCS events. For TP sensor learn procedure, refer to Powertrain Management / Computer and Control Systems / Throttle Position Sensor / Service and Repair / Throttle Position Sensor Learn Procedure. Idle Learn Procedure

DIAGNOSTIC AIDS
The Tech 1 scanner displays throttle position in voltage and percentage of throttle blade opening. With ignition "ON" or at idle, TP sensor signal voltage should display between 0.3 and 0.9 volt with the throttle closed and increase at a steady rate as throttle is moved toward WOT.

If DTC 23 or 66 is also set, check CKT 452 for being open or a faulty PCM connection.

Refer to Diagnosis By Symptom/Intermittents. - Intermittent Malfunctions