DTC 21

Throttle Position Sensor Circuit:

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 above 4 volts at Wide Open Throttle (WOT).

The TPS signal is one of the most important inputs used by the PCM for fuel control and for most of the PCM control outputs. Code 21 will set if:

^ TPS voltage is greater than 4.8 volts at any time.

OR

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

^ TPS signal voltage is greater than .80 volt.

^ Code 34 not present.

^ All conditions met for 5 seconds.

Code 21 Diagnostic Chart:

Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.

1. With closed throttle, ignition "ON," or at idle, voltage at "BB10" should be .33-.46 volt. If not, Adjustments see for adjustment procedures.

2. With the TPS sensor disconnected, the TPS voltage should go low and a Code 22 will set. This test verifies that the PCM and wiring are OK.

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


NOTE: If a Code 21 is set, the PCM will not allow 4th gear or TCC operation.


Diagnostic Aids:
The Tech 1 displays throttle position in volts. With closed throttle, ignition "ON" or at idle, voltage should be .33 - .46 volt. If not, Adjustments see for adjustment procedures.

An open in CKT 452 may result in Codes 15 and 21.

Check For:

^ Poor Connection or Damaged Harness - Inspect PCM harness connectors for backed out terminal "BB1O", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

^ Intermittent Test - Monitor TPS voltage on Tech 1 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 on Tech 1 while slowly depressing accelerator pedal with engine stopped and ignition "ON." Display should vary from closed throttle TPS voltage (.33 - .46 volt) when throttle is closed, to over 4.0 volts (4000 mV) when throttle is held at Wide Open Throttle (WOT) position. Typically, accelerator pedal travel only yields 4.1 or 4.2 volts maximum. If a TPS voltage of over 4.8 volts is observed at any point in normal accelerator pedal travel, replace TPS.