BMW Z3 Auto Trans Brake Shift Interlock Solenoid Replacement Cost

These solenoids will fail on a fair amount of vehicles. The majority will never have a problem, and many others will be due to a brake light switch failure. For this reason, it is difficult to estimate how often the brake shift interlock solenoid will fail, but considering the amount of use this solenoid endures, failure around or after 100,000 miles would be no surprise.

When diagnosing a concern of inability to remove the shifter from park, the technician will first ensure there is no issue with installing, turning, or removing the ignition key, and that the brake lights are functioning properly. Then, the technician will listen for the solenoid to make noise upon pressing the brake pedal, signifying that is is either moving or not. If nothing is heard, the technician will check fuses, if any, and check for power and ground at the solenoid. If the solenoid is receiving proper voltage and ground but fails to operate, the technician will remove, bench test, and replace the solenoid as needed.

Removal of the solenoid may involve removing a trim panel and a few fasteners, or it may require that the gear selector surround trim, console trim panel, and gear selector be removed for access. Once access is available, the solenoid will be removed from electrical connections, and linkages that are connected to the solenoid pushrod, and finally removed after disconnecting fasteners. Replacement is the reverse of removal, and the solenoid can be tested through normal operation of the gear selector and brake pedal.

Even if the brake lights work, we recommend testing the brake light switch if the brake shift interlock solenoid is not receiving power. This is because the brake light switch may have a secondary or tertiary circuit for cruise control or the brake shift interlock system. We also recommend replacing any worn bushings in the shifter assembly while it is removed or accessible. These bushings wear out and can cause failure to engage in any drive range, including park.

When no power is present to the brake shift interlock solenoid, this may not be due to a component failure, but the vehicle anti theft system could be locking the shifter to prevent operation. If the security warning light is on, flashing, or otherwise indicating it is active, consulting a technician is the preferred next step.

As this repair can range from simple to intricate, it is of importance to review the steps needed to perform this repair for the specific vehicle with a defective solenoid. This will prevent the DIY mechanic from getting too far into a job before realizing they cannot complete the repair. In most cases, this is a simple repair and an easy diagnosis as long as simple electrical circuits are understood.