The powertrain control module (PCM) performs circuit checks on the cruise control system and can set diagnostic trouble codes if a fault is detected. The PCM monitors the stop lamp circuit, the cruise control switch circuit, the cruise control clutch circuit, the cruise control move circuit and the cruise control direction circuit. If the PCM disabled the cruise control due to a fault, DTC P1584 will set and specific information regarding which type of fault set the DTC can be viewed under the scan tool Failure Record. After verifying a cruise control problem exists, retrieving DTCs should be the first step in diagnosing a cruise related problem.

The scan tool can perform a special function which can simulate cruise control module rod movement. The test will move the accelerator pedal to 50% throttle and back down to idle. This function checks the ability of the PCM to control the cruise control clutch, the direction and the move circuits. The scan tool can also display the cruise switch as well as the stop lamp switch (brake switch) states.