With 4L80E Automatic Transmission

Throttle Position Sensor Circuit Code 21:

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 about 4.0 volts at Wide Open Throttle (WOT). 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:
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 (WOT)
^ All conditions met for 1 second.
^ With throttle closed, the TPS should read less than 1.25 volts. Refer to "Diagnostic Aids".

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 volt return circuit.

Diagnostic Aids:
A Tech 1 "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 Tech 1 "Scan" tools will read throttle angle .0% = closed throttle 100% = WOT.
- Intermittent Malfunctions
Scan TP signal 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.