Shift Lever CAN Be Moved Without Brake Pedal Depressed (With Allison Transmission)

Shift Lever Can Be Moved without Brake Pedal Depressed (with Allison Transmission)

Diagnostic Fault Information

Important: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Testing and Inspection

Circuit/System Description
With the ignition in the ON position and the shift lever is in PARK, battery positive voltage is supplied from the body control module (BCM) to the automatic transmission shift lock control solenoid through the normally-closed automatic transmission shift lock control switch. When the transmission control module (TCM) indicates the shift lever is in the PARK position, the engine control module (ECM)/powertrain control module (PCM) sends a class 2 serial data message to the BCM indicating the transmission is in the PARK position. This allows current to flow through the switch to the automatic transmission shift lock control solenoid. Since the automatic transmission shift lock control solenoid is permanently grounded, the shift lock control solenoid energizes, locking the shift linkage in the PARK position. When the driver presses the brake pedal, the contacts in the automatic transmission shift lock control switch open, causing the automatic transmission shift lock control solenoid to de-energize, unlocking the shift lever from the PARK position.

Reference Information

Schematic Reference
Automatic Transmission Shift Lock Control Schematics

Connector End View Reference
Automatic Transmission Shift Lock Control Connector End Views

Electrical Information Reference
^ Circuit Testing
^ Connector Repairs
^ Testing for Intermittent Conditions and Poor Connections
^ Wiring Repairs

Circuit/System Verification
With a scan tool, monitor the Trans. Range Sw. data to verify vehicle is in the Park position.
^ If data does not display Park, replace the internal mode switch (IMS).

Circuit/System Testing
1. With the ignition ON, connect a test lamp between the A/T shift lock solenoid ground and supply voltage. Verify test lamp illuminates.
^ If the test lamp does not turn ON, repair the ground circuit.
2. With the ignition ON, connect a test lamp between the A/T shift lock solenoid supply power and a good ground. Verify the test lamp does not illuminate.
^ If the test lamp turns ON, replace the A/T shift lock solenoid.
3. Test the stop lamp switch for proper operation and supply power from the BCM.
^ If testing indicates no supply power from the BCM, refer to Circuit/System Verification. Verification Tests
4. If no trouble found in circuit, replace the BCM.

Repair Instructions

Important: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

^ Stop Lamp Switch Replacement
^ Automatic Transmission Shift Lock Actuator Replacement
^ Transmission Internal Mode Switch Replacement
^ Body Control Module Replacement for BCM