Powertrain Controls - ECM/PCM

Diagnostic Trouble Code 21:

Throttle Position Sensor Circuit:

CIRCUIT DESCRIPTION
The Throttle Position (TP) sensor provides a voltage signal that changes relative to the throttle blade position. TP sensor signal voltage will vary from about 0.5 volt at idle to about 5 volts at Wide Open Throttle (WOT).

The TP sensor signal is one of the most important inputs used by the Engine Control Module (ECM) for fuel control and for most of the ECM controlled outputs.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. Diagnostic Trouble Code (DTC) 21 will set if:

^ TP sensor signal voltage is greater than 2.5 volts.
^ Manifold Absolute Pressure (MAP) less than 52 kPa (or greater than 15 inHg).
^ All conditions met for 8 seconds.

The TP sensor has an auto zeroing feature. If the voltage reading is within the range of about 0.3 to 1.0 volt, the ECM will use that value as closed throttle. If the voltage reading is out of the auto zero range at closed throttle, check for binding throttle cable, misadjusted Traction Control System (TCS) adjuster assembly or damaged linkage.

2. With the TP sensor disconnected, the TP sensor signal voltage should go low if the ECM and wiring are OK.

3. Probing CKT 452 with a test light to 12 volts checks the sensor ground circuit. A faulty sensor ground will cause a DTC 21.

4. Refer to Diagrams/Electrical for detailed circuit description before replacing any components. Diagrams

5. If the TP sensor or throttle body is replaced, the Electronic Brake and Traction Control Module (EBTCM) must "learn" the TP sensor idle position voltage with the new component(s) installed. This is necessary to ensure effective engine torque reduction during TCS events.

THROTTLE POSITION SENSOR LEARN PROCEDURE
This procedure requires a T-1 (Tech 1 scanner) or T-100 (CAMS) unit, and is as follows using a Tech 1 scanner:

^ Ignition "OFF."
^ Connect Tech 1 scanner with Mass Storage/Chassis Cartridge.
^ Ignition "ON."
^ Follow menus to reach ABS/TCS features.
^ Select "F5: TP SENSR LRN."
^ Press the up arrow to begin learn procedure.
^ Wait for Tech 1 scanner to indicate "Complete."
^ Ignition "OFF."
^ Disconnect Tech 1 scanner.

DIAGNOSTIC AIDS
A scan tool displays throttle position in volts. With ignition "ON" or at idle, TP sensor signal voltage should display less than 1.00 volt with the throttle closed and increase at a steady rate as throttle is moved toward WOT.

If DTC 15 is also set, check CKT 452 for a faulty connection or an open.

An open in CKT 452 will result in a DTC 21.

Refer to Intermittents in Diagnosis By Symptom. Testing and Inspection