The throttle control module contains two throttle position (TP) sensors with a common 5 volt supply, a common ground, and two independent signal circuits that vary resistance according to changes in throttle plate position. The ECM measures the signal voltage from each TP sensor, which is a reduced value of the ECM 5 volt reference. As the throttle plate opens from 0% throttle to wide open throttle, the voltage on the TP sensor 1 signal increases from 0.6 (+/-0.2) volts to 4.3 (+/-0.2) volts, while the voltage on the TP sensor 2 signal decreases from 4.4 (+/-0.2) volts to 0.76 (+/-0.2) volts. DTC P0123 sets when TP sensor 1 signal voltage at the ECM is above the calibrated voltage value.

DTC P0123 will set if TP sensor 1 signal voltage at the ECM is above 4.61 volts when:

DTC P0123 diagnostic runs continuously with engine running.

P0123 is a (type A) DTC.

To locate an intermittent problem, use Scan tool to monitor TP SENSOR 1 voltage with ignition On, engine Off. Wiggling wires while watching for a change in TP SENSOR 1 voltage may locate the area where an open or a short to voltage in the wiring may exist.

A skewed TP sensor 1 can set this DTC. Check the voltage range of the sensor using THROTTLE POSITION VALVE in the SPECIAL FUNCTIONS section of the Scan tool, which will command the throttle control module to move the throttle plate. The approximate (+/- .1) TP SENSOR 1 voltages at 25% TP ANGLE intervals should be:

If there is a circuit fault detected for TP sensor 1 and TP sensor 2 in the same ignition cycle, the ECM will default to REDUCED PERFORMANCE mode for the entire ignition cycle, even if the fault is corrected.

If both P0123 and P0223 are set, circuit 486 may be shorted to voltage.

If DTCs P0103, P0108, P0113, P0118, P0123, P0223, P0341, P0406 and P1271 are set, there may be an open circuit in the 5 volt reference return circuit 652.