The auto trans shift lock control is a safety circuit that prevents the vehicle from accidentally shifting out of PARK when the ignition is in the RUN position. The steering column is equipped with a shift interlock actuator. This actuator when energized physically blocks the gear shift lever from moving out of PARK when the ignition is in the RUN position. When the driver presses the brake pedal, the auto trans shift lock control solenoid de-energizes, allowing the driver to move the gear shift lever.

The transaxle internal mode switch (IMS) determines the position of the gear shift lever and provides this information to the powertrain control module (PCM).

When the gear shift lever is in PARK, the PCM sends a Class 2 message informing the body control module (BCM) of the position of the shift lever.

When the ignition switch is in the RUN position, the BCM energizes the auto trans shift lock control solenoid. This module output applies battery positive voltage (B+). This circuit supplies battery positive voltage (B+) through the normally-closed stoplamp/auto trans shift lock control switch to the auto trans shift lock control solenoid. The solenoid, which is always grounded energizes locking the gear shift lever in the PARK position. Depressing the brake pedal opens the contacts of the stoplamp/auto trans shift lock control switch, removing power from the auto trans shift lock control solenoid. The solenoid de-energizes, allowing the driver to move the gear shift lever out of PARK.

When the gear shift lever moves out of PARK, the transaxle internal mode switch (IMS) signals the PCM of the change. The PCM provides this information to the BCM via a Class 2 message. The BCM in turn de-energizes the auto trans shift lock control solenoid. Once the vehicle is out of PARK, the auto trans shift lock control solenoid remains de-energized when the brake pedal is released and the stoplamp/auto trans shift lock control switch contacts return to their normally-closed state.

At all times the BCM internally monitors for a short to ground or a short to battery positive voltage (B+). If the BCM detects one of these conditions, the BCM sets one of the following diagnostic trouble codes:

If DTC B0802 or DTC B0803 is current in BCM memory, the BCM defaults and turns OFF the auto trans shift lock control output. Always begin diagnosis of the auto trans shift lock control solenoid with Diagnostic System Check - Automatic Transmission Shift Lock Control .