DTC 21

Code 21 Chart:

TPS Wiring Circuit:

CIRCUIT DESCRIPTION:
The Throttle Position Sensor (TPS) provides a voltage signal that changes relative to the throttle blade. Signal voltage will vary from about 0.5 at idle to about 5 volts at Wide Open Throttle (WOT). The TPS signal is one of the most important inputs used by the Electronic Control Module (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:

^ Engine is running
^ TPS signal voltage is greater than 3.7 volts
^ Air flow is less than 17 gm/sec.
^ All conditions met for 10 seconds.
OR
^ TPS signal voltage over 4.5 volts with ignition "ON."

2. With the TPS sensor, disconnected, the TPS voltage should go low if the ECM 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. Should read. 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. An open in CKT 452 will result in a Code 21. - Intermittent Malfunctions