GM Service Manual Online
For 1990-2009 cars only

Important: The automatic transmission shift lock control portion of the brake pedal position (BPP) switch (terminals E and F) contacts are closed with the brakes released. Depressing the brake pedal opens the switch contacts. Open switch contacts cause the solenoid to de-energize and unlocks the shift lever. The automatic transmission shift lock control portion of the park/neutral position and backup lamp switch contacts, terminals B and C, are closed in the PARK position only. The circuit is not active when the key in the OFF position.

The solenoid locks the shift lever mechanism in the PARK position when the automatic transmission shift lock control is energized. The automatic transmission shift lock control solenoid returns to the unlocked position when the automatic transmission shift lock control is not energized.

The following components are involved in the automatic transmission shift lock control circuit:

    • The park/neutral position and backup lamp switch
    • The brake pedal position (BPP) switch
    • The automatic transmission shift lock control solenoid

Fuse #16, TURN-B/U, supplies battery voltage (12V) to the following components in order:

  1. The ignition switch
  2. The park/neutral position and backup lamp switch
  3. The brake pedal position (BPP) switch
  4. The automatic transmission shift lock control solenoid

The energized solenoid locks the shift lever in the PARK position.

The solenoid is energized when following conditions are present:

    • The ignition switch is in the RUN or the START position.
    • The shift lever is in the PARK position.
    • The brake pedal is released.