Automatic Transmission Shift Lock Control Description and Operation with Allison Transmission
Automatic Transmission Shift Lock Control System with Allison Transmission
The automatic transmission shift lock control is a safety device that prevents
an inadvertent shift out of PARK when the ignition is ON. The driver must press the
brake pedal before moving the shift lever out of the PARK position. The system consists
of the following components:
| • | The automatic transmission shift lock control solenoid. |
| • | The automatic transmission shift lock control switch. |
| • | The body control module (BCM). |
| • | The engine control module (ECM), if equipped with a 6.6L engine. |
| • | The powertrain control module (PCM), if equipped with a 8.1L engine. |
With the ignition in the ON position and the shift lever is in PARK, battery
positive voltage is supplied from the 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 ECM/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.
Automatic Transmission Shift Lock Control Description and Operation without Allison Transmission
Automatic Transmission Shift Lock Control System
The automatic transmission shift lock control is a safety device that prevents an inadvertent shift out of PARK when the ignition is ON. The driver must press the brake pedal before moving the shift lever out of the PARK position. The system consists
of the following components:
| • | The automatic transmission shift lock control solenoid. |
| • | The automatic transmission shift lock control switch. |
| • | The park/neutral position switch. |
With the ignition in the ON position, battery positive voltage is supplied to the park/neutral position switch. When the transmission is in the PARK position the contacts in the park/neutral position switch are closed. This allows current to flow through
the switch to the automatic transmission shift lock control switch. The circuit continues through the normally-closed switch to the automatic transmission shift lock control solenoid. The automatic transmission shift lock control solenoid is permanently
grounded. This energizes the automatic transmission shift lock control solenoid, 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 release. This allows the shift lever to move from the PARK position.
