Powertrain Controls - ECM/PCM

Code 21 Diagnostic Chart:

Throttle Position (TP) Sensor Wiring Schematic:

CIRCUIT DESCRIPTION
The Throttle Position (TP) sensor provides a voltage signal that changes relative to the throttle opening. Signal voltage will vary from approximately 0.6 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.
^ No DTC 33 or 34.
^ MAP less than 65 kPa.
^ TP sensor signal voltage greater than approximately 3.9 volts.
^ Above conditions exist ror over 5 seconds. OR
^ TP sensor voltage greater than about 4.7 volts.

ACTION TAKEN (PCM WILL DEFAULT TO)
^ Malfunction Indicator Lamp (MIL) illuminates.
^ TP sensor will read 0% if engine vacuum is less than 30 kPa, 10% if engine vacuum is greater than 30 kPa or vehicle speed is greater than 2 mph.
^ 4T60E transaxle (if equipped) won't go into 4th gear or engage TCC.

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 0.900 volt. If it doesn't, check for sticking TP sensor for 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 452 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 0.200 volt to 0.900 volt with throttle closed and ignition "ON" or at idle. Voltage should increase at a steady rate as throttle is moved toward WOT.
^ A Tech-1 scan tool will also display throttle angle %, 0% closed throttle, 100% WOT.
^ An open in CKT 452 will result in a DTC 21.
^ DTCs 15, 21 and 66 stored at the same time could be the result of an open CKT 452. Scan TP sensor while depressing accelerator pedal with engine stopped and ignition "ON." Display should vary from about 0.6 volt (600 mV) when throttle is closed, to over 4500 mV (4.5 volts) 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 and/or replace if necessary.
^ Refer to "DIAGNOSIS BY SYMPTOM/INTERMITTENTS" Testing and Inspection