P0123

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 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. The DTC P0123 is a type A DTC. The DTCs P1122 is a type D DTCs.

CONDITIONS FOR SETTING THE DTC
The DTC will set under the following conditions:

^ The engine is running.
^ The Throttle Position (TP) sensor signal is greater than 4.9 volts.

ACTION TAKEN WHEN THE DTC SETS

NOTE: 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 driving trips without a fault condition present. A history DTCs will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 40°F from the start-up coolant temperature and the engine coolant temperature exceeds 160°F during that same ignition cycle) or the scan tool clearing feature has been used.

DIAGNOSTIC AIDS
The VCM pins GR 12 and GR 27 are spliced together inside the VCM. When checking one of these circuits for a problem, also check the other circuit and the components on the circuit.

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.

A DTC P0123 will result if the TP ground circuit is open or the TP signal circuit is shorted to the voltage.

A DTC P0122 will result if an open or a short to ground in the 5 volt reference circuit or the TP sensor signal circuit.

Refer to Intermittents.

TEST DESCRIPTION
The numbers below refer to step numbers on the diagnostic table.

2. If the TP signal is greater than 4.8 volts, then the fault is present.
3. With the TP sensor disconnected, the TP signal voltage should go low if the VCM and wiring are OK.
10. The VCM pins GR12 and GR27 are spliced together inside the VCM. This step isolates the two pins from one anther.