P0123

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

The Throttle Position (TP) sensor provides a voltage signal which changes relative to the throttle blade angle. The signal voltage varies from about 0.5 volt at idle to about 4.0 volts at Wide Open Throttle (WOT).

The Vehicle Control Module (VCM) uses the TP signal, one of the most important inputs, for fuel control and for most of the VCM control outputs.

Each time the voltage drops below 1.25 volts and stops, the VCM assumes this value as the 0 throttle angle, and the VCM measures the percent throttle from this point on.

CONDITIONS FOR SETTING THE DTC

The engine is running.

ACTION TAKEN WHEN THE DTC SETS

IMPORTANT: The scan tool will not indicate default values.

When the P0123 is reported and 1 failure has occurred, the VCM sets the DTC P0123, and the VCM turns ON the Malfunction Indicator Lamp (MIL).

CONDITIONS FOR CLEARING THE MIL/DTC

^ The VCM turns the MIL OFF after 3 consecutive drive trips when the test has Run and Passed and not Failed.

^ A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during the same ignition cycle).

^ Use the scan tool Clear Information function.

^ Disconnect the VCM battery feed for 30 seconds.

DIAGNOSTIC AIDS

The scan tool reads the throttle position in volts. The scan tool should read about 0.45 to 0.85 volt with the throttle closed and the ignition switch turned ON or at idle. The voltage should increase at a steady rate as the throttle is moved toward the Wide Open Throttle (WOT).

Also, some scan tools will read the throttle angle. 0% = closed throttle. 100% = WOT.

Scan the TP sensor while depressing the accelerator pedal with the engine turned off and the ignition turned on. The display should vary from below the 1.25 volts (1250 mV) when the throttle was closed to over 4.5 volts (4500 mV) when the throttle is held at WOT position.

This DTC will result if the TP ground circuit is open or the TP signal circuit is shorted to the voltage. Refer to the Symptoms.
Testing and Inspection

TEST DESCRIPTION

The numbers below refer to the step numbers in the diagnostic table.

2. If the TP signal measures greater than 4.8 volts, then the fault exists.

3. With the TP sensor disconnected and if the VCM and the wiring are okay, the TP signal should go low.

4. Probing the TP ground circuit with a test lamp checks the 5 volt return circuit. This step isolated a faulty sensor, the VCM or an open TP ground circuit.