DTC 21

Code Chart 21:

TPS Circuit:

CIRCUIT DESCRIPTION:
The Throttle Position (TP) sensor provides a voltage signal that changes relative to the throttle blade. Signal voltage will vary from about .29 at idle to about 4.8 volts at wide open throttle and is nonadjustable.

The TP sensor 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: Number(s) below refer to circled number(s) on the diagnostic chart.

1. DTC 21 will set if:

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

TP sensor: The TP sensor has an auto zeroing feature. If the voltage reading is within the range of .29 to .98 volt the ECM will use that value as closed throttle. If the voltage reading is out of the auto zero range on an existing or replacement TP sensor, make sure the cruise control and throttle cables are not being held open. If OK, replace TP sensor.

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

3. Probing CKT 452 with a test light checks the 5 volts return circuit. Faulty sensor ground circuit will cause a DTC 21.

DIAGNOSTIC AIDS:
A Tech 1 scan tool reads throttle position in volts. Voltage should increase at a steady rate as throttle is moved toward WOT.

Also, Tech 1 scan tools will read throttle angle. O% = closed throttle, 100% = WOT.

An open in CKT 452 will result in a DTC 21. - Intermittent Malfunctions