Powertrain Controls - ECM/PCM

DTC 21 Chart:

CIRCUIT DESCRIPTION
The Throttle Position (TP) sensor provides a voltage signal that will change relative to the throttle blade an angle. The signal voltage will vary from about 0.4 volt at idle to about 5 volts at wide open throttle. The PCM calculates throttle angle in percentage from the TP sensor voltage signal and auto zeros from about 0.4 volt (0%) to about 5 volt (100%). The TP sensor is one of the most important inputs used by the PCM for fuel control and other functions such as idle, Wide 0pen Throttle (WOT), deceleration enleanment, and acceleration enrichment. When the PCM detects a TP signal above the high limit and engine RPM is between 25 and 3000, DTC 21 will set.

DTC 21 WILL SET WHEN
- RPM is between 25 and 3000.
- TP sensor voltage is 4.96 or greater.

ACTION TAKEN (PCM WILL DEFAULT TO)
- With a current DTC 21 set, the PCM will illuminate the Malfunction Indicator Lamp (MIL) (Service Engine Soon).
- The PCM will disable the Torque Converter Clutch (TCC), and transaxle pressure control. The transmission will be locked in the current gear, TP, throttle angle value will be replaced with a default of 6°(7%) with a closed throttle switch and 13°(16%) with throttle switch open.

DTC 21 WILL CLEAR WHEN
The fault no longer exists.

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

1. With TP sensor or wiring shorted Tech 1 data parameter "RAW THROTTLE POS" will read 85 or greater.
2. Checking for shorted TP sensor or shorted wiring. If the data value stays greater than -7 with the sensor disconnected, the problem is in the wiring.
3. Checking for an open in CKT 808 between the TP sensor and PCM. An open in CKT 808 will cause the TP signal to always be high whenever the TP sensor is connected.

DIAGNOSTIC AIDS
The Tech 1 displays throttle position in volts. With closed throttle, ignition "ON" or at idle Tech 1 should display 0.4 volt. If not, refer to Throttle Position Sensor for replacement procedures.
An open in sensor ground CKT 808 may result in DTCs 14, 21, 22, and 120. Refer to Intermittents in Diagnosis by Symptom. - Intermittent Malfunctions
Check for:

Poor connection or damaged harness
Inspect PCM harness connectors for backed out terminal "B15" or "C1", improper mating broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

Intermittent test
Monitor TP sensor voltage on Tech 1 while moving related connectors and wiring harness. If the failure is induced, the display will change. This may help to isolate the location of the malfunction.

TP sensor scaling
Observe TP sensor voltage display while depressing accelerator pedal, with engine stopped and ignition "ON". Display should vary from closed throttle TP sensor voltage when throttle is closed (0.4 volt) to over 5 volts when throttle is held at Wide Open Throttle (WOT) position.