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 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 P1526 will set if the throttle has not been learned after the ECM has been reprogrammed, OR the learned rest position TP values do not match the stored learned values within a certain range.

DTC  P1526 will set if the throttle has not been learned after the ECM has been reprogrammed.

The learned lower rest position TP values are too far out of range from the stored learned values when:

DTC P1526 diagnostic runs during a key-up closed throttle test when the above conditions have been met.

DTC P1526 is a type D DTC.

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

Important: If a TP sensor 1 or 2 DTC is also set, diagnose that DTC first. Then if DTC P1516 is also set, diagnose that DTC next. Then if DTC P1510 is also set, diagnose that DTC next.

Important: DTC P1526 must have a key cycle to clear. Therefore, it may take 2 times to clear the DTC from the ECM memory.

If DTC P1526 is set, the ECM will default to 1 of the 2 limp home modes, random injector disable with engine speed limited to 1,800 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.

The throttle body relearn procedure should be performed anytime a throttle body has been replaced or an ECM has been replaced or reprogrammed.

The ECM will start at 29 seconds to cycle the throttle plate from the rest position to full closed, then from the full closed position to around 10 percent. This will take about 3 seconds. The ECM will then return the throttle to the rest position. During this throttle plate cycle, the ECM will have learned the lower and rest position TP sensor values, actuator motor torque to overcome spring pressure, as well as both spring return rates.