Powertrain Controls - ECM/PCM

Code 21 Chart:

Code 21 Wiring Diagram:

CIRCUIT DESCRIPTION:

The throttle position sensor (TPS) provides a voltage signal that changes relative to throttle blade angle. Signal voltage will vary from about .4 at idle to about 5 volts at wide open throttle. 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 ECM CONNECTOR IDENTIFICATION under ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS for correct color code identification of circuit.

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

1. Code 21 will set if:

^ TPS voltage is greater than 4.9 volts at any time.

^ Engine is running and air now is less than 15 gm/sec.

^ TPS signal voltage is greater than 2.5 volts.

^ Code 34 not present.

^ All conditions met for 5 seconds

^ With closed throttle, ignition "ON," .or at idle, voltage at YD13 should be .33-.46 volt If not adjust TPS.

2. When the TPS sensor is disconnected, the TPS voltage will go low and a Code 22 will set. Therefore, the ECM and wiring are OK.

3. Probing CKT 452 with a test light checks the sensor ground CKT. A faulty sensor ground circuit will cause a Code 21.

NOTE: If a Code 21 is set, the ECM will use a defaulted value for TPS of about .5 volt.

DIAGNOSTIC AIDS:

^ Scan tool reads throttle position in volts. With closed throttle, ignition ON or at idle, voltage should be .33-.46 volts.

^ Also some "Scan" tools will read throttle angle 0% = closed throttle 100% = WOT. An open in CKT 452 will result in a Code 21. Refer to TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/INTERMITTENTS.

Check For:

^ Poor Connection or Damaged Harness Inspect ECM harness connectors for backed out terminal "YD13, 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 TPS 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

^ 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 throttle was closed, to over 4.5 volts (4500 mV) when throttle is held at wide open throttle position.