Powertrain Controls - ECM/PCM

DTC 21 Chart:

Throttle Position (TP) Sensor Schematic:

CIRCUIT DESCRIPTION
The Throttle Position (TP) sensor provides an output voltage relative to throttle position angle. The Powertrain Control Module (PCM) supplies a 5 volt reference and a ground to the TP sensor and monitors the voltage returned. The TP sensor voltage will vary from 0.2V to 0.9V at idle or with ignition "ON" and engine "OFF" to over 4.5V at wide open throttle.

DIAGNOSTIC TROUBLE CODE (DTC) 21 WILL SET WHEN
^ Engine speed is below 1500 RPM.
^ DTC 33 or 34 is not set.
^ Manifold Absolute Pressure (MAP) is less than 65 kPa.
^ TP sensor signal voltage is greater than 3.9 volts.
^ Above conditions exist for more than 5 seconds.

OR

^ TP sensor voltage is greater than 4.7 volts.

ACTION TAKEN (PCM WILL DEFAULT TO)
The Malfunction Indicator Lamp (MIL) will illuminate. If the Vehicle speed Sensor (VSS) reads less than 2 mph, the TP sensor will default to 0%. If VSS reads greater than 2 mph, the TP sensor will default to 10%. 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 0.900 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 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 should display between 0.2V and 0.9V with throttle closed and ignition "ON" or at idle. Voltage should increase at a steady rate as throttle moves toward Wide Open Throttle (WOT).
^ DTCs 21 and 23 stored at the same time could be the result of an open CKT 452. Scan TP sensor while depressing accelerator pedal with engine "OFF" and ignition "ON." Display should vary from 0.2V when throttle is closed, to over 4.5V 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