Powertrain Controls - ECM/PCM

DTC 21 Diagnostic Chart:

Throttle Position (TP) 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 Powertrain Control Module (PCM) for fuel control and for most of the PCM control outputs.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.
1. DTC 21 will set if:
^ Engine running.
^ TP sensor signal voltage is greater than or equal to 4.9 volts at Wide Open Throttle (WOT).
^ All conditions met for 4 seconds.
With throttle closed, the TP signal should read less than 1.25 volts. Refer to "Diagnostic Aids."
2. With the TP sensor disconnected, the TP signal voltage should go low if the PCM and wiring are OK.
3. Probing CKT 452 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 volt 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 volt (1250 mV) when throttle was closed, to over 4.0 volts (4000 mV) when throttle is held at Wide Open Throttle (WOT) position.