Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Description & Operation: Introduction
The automatic transmission (A/T) shift lock control system is a safety device that prevents an inadvertent shift out of Park when the engine is running. The driver must press the brake pedal before moving the shift lever out of the Park position. The system consists of the following components:
- A/T shift lock solenoid (also known as "actuator", "shift lock solenoid" or "BTSI solenoid").
- A/T shift lock control switch (part of stoplamp switch).
- Body Control Module (BCM).
- Powertrain Control Module (PCM).
With the ignition switch in the ON position, battery voltage is supplied to the stoplamp switch. The circuit continues through the normally closed switch to the A/T shift lock solenoid. The BCM provides a ground for the A/T shift lock solenoid when the transmission is in Park. The BCM receives the transmission gear position information via class 2 serial data from the PCM. This causes the A/T shift lock solenoid to energize and lock the shift lever in the Park position. When the driver presses the brake pedal, the contacts in the stoplamp switch open. This causes the A/T shift lock solenoid to release. This allows the shift lever to move from the Park position. The BCM turns off the A/T shift lock solenoid ground circuit when the transmission is out of Park.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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