DTC 21

Chart - Code 21 Throttle Position Sensor (Signal Voltage High):

Wiring Diagram for Throttle Position Sensor Circuit.:

CODE 21 - THROTTLE POSITION SENSOR (TPS) CIRCUIT (SIGNAL VOLTAGE HIGH)


Circuit Decription:
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 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.


Test Description:Numbers below refer to circled numbers on the diagnostic chart.
1. Code 21 will set if:
TPS signal voltage is greater than 2.5 volts
Engine is running
Air flow is less than 12 gm/sec.
All conditions met for 3 seconds.
OR
TPS signal voltage over 4.5 volts with ignition "ON".
With throttle closed the TPS should read less than .62 volt. If it doesn't check adjustment.
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 checks the 5 volt return CKT, because a faulty 5 volt return will cause a Code 21.


Diagnostic Aids:

A "Scan" tool reads throttle position in volts. Should read .54V +/- .08V with throttle closed and ignition on or at idle. Voltage should increase at a steady rate as throttle is moved toward WOT. An open in CKT 452 will result in a Code 21, Refer to "Intermittents" in DIAGNOSIS BY SYMPTOM - NO TROUBLE CODE STORED.