DTC 21

Chart Code 21:

Throttle Position Sensor (TPS) 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 0.29 at idle to about 4.8 volts at wide open throttle. 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 3.75 volts.
^ Air flow is less than 17 GM/sec.
^ All conditions met for 10 seconds.

OR

^ TPS signal voltage over 4.8 volts with ignition "ON".

^ TPS check: The TPS has an auto zeroing feature. If the voltage reading is within the range of 0.29 to 0.98 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 TPS, the TPS should be adjusted. Refer to Fuel Delivery and Air Induction / Throttle Position Sensor.

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

3. Probing Circuit (CKT) 452 with a test light checks the 5 volts return circuit, because a faulty 5 volts return will cause a Code 21.

DIAGNOSTIC AIDS
A "Scan" tool reads throttle position in volts. Voltage should increase at a steady rate as throttle is moved toward wide open throttle. Also, some "Scan" tools will read throttle angle 0% = closed throttle, 100% = wide open throttle. An open in CKT 452 will result in a Code 21. Refer to Diagnosis by Symptom / Intermittents. - Intermittent Malfunctions