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Code Chart 21:

TPS Circuit:

CIRCUIT DESCRIPTION:
The Throttle Position (TP) sensor provides a voltage signal that changes relative to the throttle valve. Signal voltage will vary from about 0.33 to 1.33 volts at idle to about 4.5 volts at Wide Open Throttle (WOT). The TPS signal is one of the most important inputs used by the ECM for fuel control and for most of the ECM controlled outputs.

TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. A DTC 21 will set under the following conditions:

^ TP sensor reading below 1.9 volts or above 4.9 volts for about 64 seconds.
OR
^ TP sensor reading above 3.9 volts, but below 4.9 volts.
^ MAP reading below 65 kPa.
^ Engine speed less than 1,750 RPM.
^ All of the above conditions present for about 5 seconds.

The TP sensor has an auto zeroing feature. If the voltage reading is within the range of about .33 to 1.33 volts, the ECM will use that value as closed throttle. If the voltage reading is outside of the auto zero range at closed throttle, check for a binding throttle cable or damaged linkage. If OK, continue with diagnosis.

2. If the ECM recognizes the change of state, the ECM and CKTs 416 and 417 are OK.

3. This step isolates a faulty sensor, ECM, or an open CKT 469. If CKT 469 is open, DTC 23 may also be stored.

DIAGNOSTIC AIDS:
A "Scan" tool displays TP in volts. Closed throttle voltage should be between 0.33 to 1.33 volts, and the voltage value should increase at a steady rate as the throttle is opened. If DTC 21 is intermittent, Testing and Inspection