P0123

Intake Air Temperature (IAT), Engine Coolant Temperature (ECT), Throttle Position (TP), And Trans Temperature Sensors Wiring Schematic:

*** This information has been updated according to Technical Service Bulletin #416512, dated May 1994.

CIRCUIT DESCRIPTION
The Throttle Position (TP) sensor provides a voltage signal that changes relative to throttle blade angle. Signal voltage will vary from 0.2 - 0.74 volt at idle to above 4 volts at Wide Open Throttle (WOT).

The TP signal is one of the most important inputs used by the PCM for fuel control and for most of the PCM control outputs.

DTC PO123 WILL SET WHEN:
^ TP sensor voltage is greater than 4.8 volts at any time. OR
^ Engine is running and air flow is less than 15 gm/sec.
^ TP sensor signal voltage is greater than 1.1 volts.
^ DTC PO101 not present.
^ All conditions met for 5 seconds.

ACTION TAKEN (PCM will default to):
If a DTC P0123 is set, the PCM will not allow cruise control, 4th gear or TCC operation. The MIL (Service Engine Soon) will be illuminated.

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 "BF11" should be 0.2-0.74 volt.
2. With the TP sensor disconnected, the TP sensor voltage should go low and a DTC P0122 will set. This test verifies that the PCM and wiring are OK.
3. Probing CKT 808 with a test light checks the sensor ground circuit. A faulty sensor ground circuit will cause a DTC P0123.

DIAGNOSTIC AIDS
The Tech 1 displays throttle position in volts. With closed throttle, ignition "ON" or at idle, voltage should be 0.2 - 0.74 volt.

An open in sensor ground CKT 808 may result in DTCs P0117 and P0123. Refer to "INTERMITTENTS" under "DIAGNOSIS BY SYMPTOM". - Intermittent Malfunctions

Check for:
^ Poor connection or damaged harness - Inspect PCM harness connectors for backed out terminal "BF11" or "BE5", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

^ Intermittent test - Monitor TP sensor 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.

^ TP sensor scaling - Observe TP sensor voltage display on Tech 1 while slowly depressing accelerator pedal with engine stopped and ignition "ON." Display should vary from closed throttle TP sensor voltage (0.2 - 0.74 volt) when throttle is closed, to over 4.0 volts (4000 mV) when throttle is held at WOT. Typically, accelerator pedal travel only yields 4.1 or 4.2 volts maximum. If a TP sensor voltage of over 4.8 volts is observed at any point in normal accelerator pedal travel, replace TP sensor.