DTC 21

Throttle Position Sensor (TPS) Circuit 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 0.5 at idle to about 5 volts at wide open throttle. 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:

^ Engine is running
^ No codes 33 or 34 present.
^ TPS signal voltage is greater than 3.78 volts.
^ Air flow is calculated at less than 17 gm/sec.
^ All conditions exist continuously for 1.25 seconds.

With throttle closed, TPS signal voltage should be less than 0.98 volt. If voltage is greater than specified, check that throttle is closing completely. Make sure cruise control and throttle cables are adjusted properly, and are not sticking or binding.

TEST DESCRIPTION

Code 21 Diagnostic Chart:

Numbers below refer to circled numbers on diagnostic chart.
1. With closed throttle, ignition "ON," or at idle, voltage at PCM terminal C15 should be approx. 0.5 volt.
2. When the TPS sensor is disconnected, the TPS voltage should go low and a Code 22 will set, indicating the PCM and wiring are OK.
3. Probing circuit 808 with a test light connected to battery power checks the sensor ground. A faulty sensor ground circuit will cause Codes 15 and 21 and will turn the temp. warning light "ON".

DIAGNOSTIC AIDS:

^ Scan tool reads throttle position in volts. With closed throttle, ignition "ON" or at idle, voltage should be approx. 0.5 volt.
^ Also some "Scan" tools will read throttle angle as a percentage. 0% = closed throttle, 100% = WOT. An open in CKT 808 will result in a Codes 15 and 21 and will turn the temp. warning light "ON".

Check For:

^ Poor Connection or Damaged Harness Inspect PCM harness connectors for backed out terminals 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 approx. 0.5 volt, when throttle was closed, to over 4.0 volts when throttle is wide open. Typically, accelerator pedal fully depressed should yield approx. 4.1 - 4.2 volts from the sensor. If voltage is greater than 4.8 volts at any time while operating throttle with accelerator pedal, replace the TPS.

^ Codes 15 and 21 together indicate a possible open sensor ground circuit (circuit 808).