With 4L80 Transmission

Throttle Position Sensor 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 volt at idle to over 4.0 volts at Wide Open Throttle (WOT).

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

Code 21. 1991 C/K models w/diesel engine:

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the 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 one second.

2. With throttle closed, the TPS should read less than 1.25 volts. See "Diagnostic Aids."

3. With the TPS sensor disconnected, the TPS voltage should go low if the PCM/TCM and wiring are OK.

4. Probing CKT 452 with a test light checks the 5 volts return circuit.


DIAGNOSTIC AIDS
A "Scan" tool reads throttle position in volts and should read about .5 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 4.0 volts (4000 mV) when throttle is held at Wide Open Throttle (WOT) position.