Powertrain Control Module - PCM

Diagnostic Trouble Code 21:

TP Sensor Circuit:

CIRCUIT DESCRIPTION
The Throttle Position (TP) sensor provides a voltage signal that changes relative to the throttle blade angle. Signal voltage will vary from about 0.5 volt at idle to about 4.0 volts at Wide Open Throttle (WOT).

The TP signal is one of the most important inputs used by the PCM for fuel control and for most of the PCM control outputs.

DTC 21 WILL SET WHEN
^ Engine running.
^ TP sensor signal voltage is greater than or equal to 4.9 volts at WOT.
^ All conditions met for greater than 4 seconds.

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

DTC 21 WILL CLEAR WHEN
Conditions for fault are no longer present and Tech 1 "clear DTCs" function is used or 50 ignition switch keycycles have passed with no further faults or ignition switch is turned "OFF" and battery feed voltage is removed for 10 seconds.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Verifies TP signal display.

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

3. Probing TP sensor ground circuit with a test light checks the 5 volt return circuit.

DIAGNOSTIC AIDS
A Tech 1 scan tool reads throttle position in volts and should read about 0.5 to 1.25 volts with throttle closed and ignition "ON" or at idle. Voltage should increase at a steady rate as throttle is moved toward WOT.

Also some Tech 1 scan tools will read throttle angle 0% = closed throttle 100% WOT.

Refer to Diagnosis By Symptom / Intermittents - Intermittent Malfunctions

Scan TP signal while depressing accelerator pedal with engine stopped and ignition "ON." Display should vary from below 1.25 volts (1250 mV) when throttle was closed, to over 4.0 volts (4000 mV) when throttle is held at WOT position.