DTC 21

Code 21 Chart:

Code 21 Wiring Diagram:

CIRCUIT DESCRIPTION:


The Throttle Position Sensor (TPS) provides a voltage signal that changes relative to the throttle opening. Signal voltage will vary from about 0.5 volt at idle to about 5 volt 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.

NOTE: Because of all the possible color code combinations used on electrical wiring diagrams, always refer to SCHEMATIC DIAGRAMS/ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS/ECM CONNECTOR IDENTIFICATION for correct color code identification of circuit.

Code 21 will set if:

^ TPS voltage is greater than 4.9 volts at any time

OR

^ Engine is running and air flow is less than 15 gm/sec.
^ Engine speed is greater than 600 rpm.
^ No Code 33.
^ TPS signal voltage greater than approximately 1.5 volts (30%)
^ Above conditions exist for over 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 0.33 volts to 0.46 volts. If not, see adjustment procedures for the fuel metering section.

2. When the TPS sensor is disconnected, the TPS voltage will go low and a code 22 will set. Therefor, the ECM and wiring are good.

3. Probing CKT 452 with a test light checks the TPS ground circuit because an open or very high resistance ground circuit will cause a Code 21.


DIAGNOSTIC AIDS:


^ A "Scan" tool displays throttle position in volts. It should display 0.33 volt TO 0.46 volts with throttle closed and ignition "ON" or at idle. Voltage should increase at a steady rate as throttle is moved toward wide open throttle (WOT).

^ Also some "Scan" tools will display throttle angle. 0% = closed throttle 100% = WOT.

^ An open in CKT 452 will result in a Code 21.

^ Poor connection or damaged harness. Inspect ECM harness connectors for backed out terminals BB6, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

^ Intermissent test. If connections and harness check good, monitor TPS voltage while moving related connectors and wiring harness. If the failure is induced, the display will change. This may also help to lacate the location of the malfunction.

^ TPS scaling. Observe TPS voltage display while depressing accelerator pedal with engine stopped and ignition "ON". Display should vary from closed throttle TPS voltage when the throttle was closed to over 4.5 volts when the throttle is held at wide open throttle position.

^ Refer to TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/INTERMITTENTS.