Powertrain Controls - ECM/PCM

Code Chart 21:

TPS Circuit:

CIRCUIT DESCRIPTION:
The Throttle Position (TP) sensor provides a voltage signal that changes relative to the throttle blade angle. Signal voltage will vary from about 0.2-.74 volt at idle to above 4.0 volts at wide open throttle (WOT).

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.

DTC 21 will set if:

^ TP sensor voltage is greater than 5 volts at any time.
OR
^ Engine is running and air now is less than 15 gm/sec.
^ Throttle angle is greater than 30%.
^ DTC 34 not present.
^ All conditions met for 5 seconds.

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

1. With closed throttle, ignition "ON," or at idle, voltage at "YF13" should be 0.2-0.74 volts. If not adjust TP sensor. See TP sensor ADJUSTMENT under ADJUSTMENTS.

2. When the TP sensor is disconnected, the TP sensor voltage should go low and DTC 22 will set. This test verifies that the ECM and wiring are OK.

3. Probing circuit 452 with a test light checks the TP sensor ground circuit. A faulty sensor ground circuit will cause DTC 21 to be set.

NOTE: If DTC 21 is set, the ECM will use a default value for TP sensor of 3% throttle angle. The scan tool will continue to display actual sensor value.

DIAGNOSTIC AIDS:

^ Scan tool reads throttle position in volts. With closed throttle, ignition "ON" or at idle, voltage should be 0.2-0.74 volts. If not, adjust TP sensor. See TP sensor ADJUSTMENT under ADJUSTMENTS.
^ An open in CKT 452 will result in a DTC 21.

Check For:

^ Poor Connection or Damaged Harness Inspect ECM harness connectors for backed out terminal "BB6," improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.
^ Intermittent Test. If connections and harness check OK, monitor TP sensor voltage while moving related connectors and wiring harness. If the failure is induced, the display will change. This may help to isolate the location of the malfunction.
^ TP sensor Scaling. Observe TP sensor voltage display while depressing accelerator pedal with engine stopped and ignition "ON." Display should vary from .2-.74 volt when throttle is closed to over 4 volts when throttle is held at wide open throttle position.