Powertrain Controls - ECM/PCM

DTC 21 - Throttle Position Sensor Circuit (Signal Voltage High):

Throttle Position Sensor Wiring Circuit:

Circuit Description:
The Throttle Position (TP) sensor provides a voltage signal that changes relative to the throttle opening. Signal voltage will vary from approximately .6 volt at idle to about 4.8 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 control outputs.

DTC 21 Will Set When:
^ Engine is running below 1500 RPM.
^ DTC 33 or 34 is not set.
^ MAP is less than 65 kPa.
^ TP sensor signal voltage is greater than approximately 3.9 volts.
^ Above conditions exist for more than 5 seconds. OR
^ TP sensor voltage is greater than about 4.7 volts.

Action Taken (PCM will default to): The Malfunction Indicator Lamp (MIL) will illuminate. TP sensor will read 0% if engine vacuum is less than 30 kPa. TP sensor will read 10% if engine vacuum is greater than 30 kPa or vehicle speed is greater than 2 mph. The cooling fan will enable.

DTC Chart Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. With throttle closed the TP sensor should read less than .900 volt. If it doesn't, check for sticking TP sensor or throttle linkage. If OK, replace TP sensor.
2. With the TP sensor disconnected, the TP sensor voltage should go low if the PCM and wiring are OK.
3. Probing CKT 808 with a test light checks the TP sensor ground circuit because an open or very high resistance ground circuit will cause a DTC 21.

Diagnostic Aids: A Tech 1 scan tool displays throttle position in volts. It should display between 200 mV and 900 mV with throttle closed and ignition "ON" or at idle. Voltage should increase at a steady rate as throttle is moved toward Wide Open Throttle (WOT)

A Tech I scan tool will display throttle angle %, 0% closed throttle; 100% WOT.

An open in CKT 808 will result in a DTC 21.

DTCs 15 and 21 stored at the same time could be the result of an open CKT 808. Scan TP sensor while depressing accelerator pedal with engine "OFF" and ignition "ON." Display should vary from about .6 volt (600 mV) when throttle is closed, to over 4.8 volts (4800 mV) when throttle is held wide open.

Check condition of connector and sensor terminals for moisture or corrosion, and clean or replace as necessary. If corrosion is found, check condition of connector seal, repair or replace if necessary.

Refer to "Intermittents," in "Diagnosis By Symptom." - Intermittent Malfunctions