The throttle actuator control (TAC) module contains a direct current actuator motor controlled by the engine control module (ECM) used to move the throttle plate, in either direction, and 2 throttle position (TP) sensors to determine the throttle plate position. The throttle plate is held at a 7 percent rest position to a mechanical stop by a constant force return spring. This spring will hold the throttle plate to the stop when there is no current flowing to the actuator motor. There is another return spring, which creates constant force on the throttle plate only when the throttle plate is moved towards the full closed position. The ECM will monitor both the actuator motor and TP sensors for circuit faults as well as check to make sure both springs can return the throttle to the 7 percent position no matter where the throttle plate remains.

The ECM will go through a throttle relearn procedure 29 seconds after the ignition is turned ON with the engine OFF as long as certain conditions have been met. During this learn procedure, the ECM will move the throttle from the rest to full closed position, then to around 14 percent. During this period, the TP sensors lower limits, rest position of the TP sensors, the actuator motor force to overcome both spring pressures as well as the return rates of both springs are learned. If any of these parameters are out of range, a DTC will be set. DTC P1511 will set if the throttle position falls outside a calibrated range when no current is applied to the throttle actuator motor during a throttle relearn procedure indicating the rest position is not being reached.

DTC P1511 will set if the throttle position is NOT in the range of 3.8-11.7 percent when commanded to the rest position, no current flowing to actuator motor, during a throttle relearn procedure when:

DTC P1511 diagnostic runs continuously during a throttle relearn procedure when the above conditions have been met.

DTC P1511 is a type A and B DTC.

The malfunction indicator lamp (MIL) will illuminate after 5 seconds.

Important: If a TP sensor 1 or 2 DTC is set, diagnose that DTC first.

If DTC P1511 is set, the ECM will default to one of the 2 limp home modes, random injector disable with the engine speed limited to 1800 RPM. The REDUCED POWER telltale will be illuminated and the ECM will remain in this condition for the entire ignition cycle even if the fault is corrected.

Possible causes of DTC P1511:

Refer to DTC P0121 Diagnostic Aids to test for a skewed TP sensor 1 or skewed TP sensor 2.