The automatic transmission 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:
The BCM controls the voltage to the shift lock control solenoid through the shift lock control solenoid controlled voltage circuit. The following conditions must be met before the BCM will supply voltage to the shift lock solenoid:
Since the shift lock control solenoid is permanently grounded, the BCM supplies voltage to the automatic transmission shift lock control solenoid, mechanically locking the shift lever in the PARK position as the solenoid energizes. When the brake pedal is applied, the BCM turns the control voltage output of the shift lock control solenoid OFF, de-energizing the shift lock control solenoid. The de-energized solenoid releases the mechanical lock allowing the driver to move the shift lever out of the PARK position. When the transmission is out of the PARK position, the shift lock control solenoid remains de-energized.
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The automatic transmission shift lock control solenoid
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The body control module (BCM)
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The powertrain control module (PCM) or the transmission control module (TCM).
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The ignition is in the ON position.
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The PCM / TCM sends an input to the BCM indicating the transmission is in the PARK position.
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The BCM determines the brake pedal is not applied according the brake pedal position.
The body control module (BCM) controls the A/T shift lock control solenoid by providing battery voltage to the A/T shift lock control solenoid. The BCM utilizes a smart driver to control the voltage supplied to the A/T shift lock control solenoid. The smart driver monitors the voltage and current flow of the control circuit.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC B2705 Gearshift Unlock Circuit
You could have a bad brake light switch ,
automatic transmission shift lock control solenoid.
the BCM or wiring problem
Install a scan tool. Turn ON the ignition, with the engine OFF. Press and release the brake pedal several times while observing the BTSI solenoid parameter in the body control module (BCM) output data list
SOURCE: 2006 Uplander: My 2006 Chevrolet tranmission is starting to shift...
take it to a dealer for diagnosis..
SOURCE: I had problems shifting into park .Now I can shift
The problem is the shift cable out of adjustment or broken. There is an adjustment tab in the cable, usually at the top of the tranny (sometimes at the shifter in the colomn). Readjust cable or new cable in neutral position.
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