The throttle actuator control (TAC) 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 0.50 volts to 4.25 volts (+/- 0.1 volts), while the voltage on the TP sensor 2 signal decreases from 4.45 volts to 0.70 volts (+/- 0.1 volts). DTC P0123 sets when TP sensor 1 signal voltage at the ECM is above the calibrated voltage value.
DTC Parameters
DTC PO123 will set if TP sensor 1 signal voltage is greater than 4.61 volts when:
| • | The condition exists for longer than 140 ms. |
| • | The battery voltage greater than 7.0 volts. |
DTC P0123 diagnostic runs continuously with engine running.
P0123 is a type A DTC for 2002, type B DTC for 2003.
Important: The MIL will only illuminate if the fault is present for longer than 5 seconds (2002 only).
Diagnostic Aids
To locate an intermittent problem, use the scan tool to monitor TP SENSOR 1 voltage with ignition On, engine Off. Wiggling the wires while watching for a change in TP SENSOR 1 voltage may locate the area where an open or short to voltage in the wiring may exist.
An intermittent open in TP sensor 1 can set this DTC. Monitor the voltage range of the sensor using THROTTLE ACTUATOR CONTROL in the SPECIAL FUNCTIONS section of the scan tool, which will command the throttle control module to move the throttle plate.
If a TP sensor 1 circuit fault is detected, the ECM will default to REDUCED POWER mode if vehicle speed is below 56 km/h (35 mph) with APP angle at 0%. Otherwise, when the circuit fault occurs, TP sensor 2 will be used and vehicle performance will not be affected. NOTE: The ECM will remain in these conditions for the entire ignition cycle even if the fault is corrected.
Circuit 486 (TP sensor 1/TP sensor 2) and circuit 1274 (APP sensor 2) share the same 5-volt reference supply (5-volt Ref-B).
The CMP/ECT/IAT/EGR/MAF/MAP/TP1/TP2 sensors share the same sensor return circuit 652.
Important: TP ANGLE on scan tool is based off of TP sensor 1 only.
