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 P0122 sets when TP sensor 1 signal voltage at the ECM is below the calibrated voltage value.

DTC P0122 will set if TP sensor 1 signal voltage is less than 0.20 volts when:

DTC P0122 diagnostic runs continuously with engine running.

P0122 is a type A DTC for 2002, type B DTC for 2003.

Important: NOTE: The MIL will only illuminate if the fault is present for longer than 5 seconds (2002 only).

To locate an intermittent problem, use the scan tool to monitor the 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 in the 5- volt reference or a short to ground in the wiring may exist.

If a TP 1 sensor circuit fault is detected, the ECM will default to REDUCED POWER mode if the 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.