With 4L80 Automatic Transmission

Code 21 Throttle Position Sensor Circuit:

Wiring Diagram For Code 21 Throttle Position Sensor Circuit:

CODE 21 - THROTTLE POSITION SENSOR (TPS) CIRCUIT


CIRCUIT DESCRIPTION:

The Throttle Position Sensor (TPS) provides a voltage signal that changes relative to the throttle blade angle. Signal voltage will vary from about .5 volts at idle to about 5 volts at wide open throttle.

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


TEST DESCRIPTION: Step numbers refer to step numbers on diagnostic chart.

1. Code 21 will set if:

^ Engine running
^ TPS signal voltage is greater than about 4.9 volts at wide open throttle.
^ All conditions met for 1 second.
^ TPS signal voltage over 4.5 volts with ignition "ON").

With throttle closed, the TPS should read less than 1.25 volts. If it doesn't, check adjustment.

2. With the TPS sensor disconnected, the TPS voltage should go low if the PCM and wiring is OK.

3. Probing CKT 452 with a test light checks the 5 volts return CKT, because a faulty 5 volts return will cause a Code 21.


DIAGNOSTIC AIDS:

A "Scan" tool reads throttle position in volts and should read about .5 volt to 1.25 volts with throttle closed and ignition on or at idle. Voltage should increase at a steady rate as throttle is moved toward WOT.

Also some "Scan" tools will read throttle angle. 0% = closed throttle 100% = WOT.

"Scan" TPS while depressing accelerator pedal with engine stopped and ignition "ON". Display should vary from below 1.25 volts (1250 mv) when throttle was closed, to over 4.5 volts (4500 mv) when throttle is held at wide open throttle position.

SEE DIAGNOSIS BY SYMPTOM - NO TROUBLE CODES STORED.