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 volts at idle to about 5.0 volts at Wide Open Throttle (WOT).

The TP sensor signal is one of the most important inputs used by the PCM for fuel control and for most of the Powertrain Control Module (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 WILL DEFAULT TO)
The Malfunction Indicator Lamp (MIL) will illuminate, 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
Number(s) below refer to circled number(s) 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 throttle shaft.
2. With the TP sensor disconnected, the TP sensor voltage should go low, if the PCM and wiring are OK.
3. Probing CKT 470 with a test light to 12 volts checks the sensor ground. A faulty sensor ground will cause a DTC 21.

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 volts with the throttle closed and increase at a steady rate as throttle is moved toward WOT.

If DTC 15 or 59 is also set, check CKT 470 for being open or a faulty PCM connection.
Refer to Diagnosis by Symptom/Intermittents. - Intermittent Malfunctions