Part 1 of 2

Code Chart 21 (Part 1 Of 2):

Throttle Postion Sensor Circuit:

CIRCUIT DESCRIPTION:

The Throttle Position Sensor (TPS) provides a voltage signal that changes relative to the throttle valve position. Signal voltage will vary from less than 1.25 volts at idle to about 5.0 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 control outputs.

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

1. This step checks to see if Code 21 is the result of a hard failure or an intermittent conidition.

Code 21 will set if:

^ Engine speed less than 1800 rpm.
^ TPS reading above 2.5 volts.
^ MAP reading below 60 kPa.
^ Above conditions exist for 2 seconds.

2. This step simulates conditions for a Code 21 (signal voltage low). If the ECM recognizes the change, the ECM, and the PPL/RED wire and the PPL/ORN wire are OK.

3. This step isolates a faulty sensor ECM or an open BLK/WHT wire. If the BLK/WHT wire is open, there may also be a Code 23.

DIAGNOSTIC AIDS:

A Scan tool displays throttle postion in volts. Closed throttle voltage should be less than 1.25 volts. TPS voltage should increase at a steady rate as throttle is moved to WOT. A Code 21 will result if BLK/WHT wire is open or PPL/RED wire is shorted to voltage. If Code 21 is intermittent, Testing and Inspection

NOTE: On the 1.8L DOHC vehicles with A/T transaxles, the "ECONO" light will also be flashing when Code 21 is logged in the ECM's memory or the circuit fault is still present. A wrong programmed EPROM may also cause the "ECONO" light to be flashing.