DTC 21

Code 21 Diagnostic Chart:

Circuit Description
The Throttle Position Sensor (TPS) provides a voltage signal that changes relative to the throttle blade. Signal voltage will vary from about .5 at idle to about 4.5 volts at Wide Open Throttle (WOT).

The TPS signal is one of the most important inputs used by the ECM for fuel control and for most of the ECM control outputs.

Code 21 Diagnostic Chart:

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

1. Code 21 will set if:
^ TPS signal voltage is greater than 3.1 volts.
^ All conditions met for 2 seconds.
^ MAP less than 52 kPa.

2. With the TPS sensor disconnected, the TPS 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 Code 21.


Diagnostic Aids
A Tech 1 "Scan" tool reads throttle position in volts. Should read less than 1.25 volts 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). An open in CKT 452 will result in a Code 21. - Intermittent Malfunctions