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The body control module (BCM)
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The powertrain control module (PCM) or the transmission control module (TCM).
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:
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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.
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.
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
Symptom:
P-0753 TRANS 3-4 SHIFT SOLENOID/TRANS RELAY CIRCUITS
When Monitored and Set Condition:
P-0753 TRANS 3-4 SHIFT SOLENOID/TRANS RELAY CIRCUITS
When Monitored: Continuously with the key on.
Set Condition: This code is set if the voltage detected on the 3-4 Shift Solenoid Control
Circuit at the PCM is different than the expected voltage.
POSSIBLE CAUSES
FUSED B(+) FEED TO THE TRANS CONTROL RELAY OPEN
3-4 SOLENOID WIRING HARNESS INTERMITTENT DEF
3-4 SOLENOID WIRING HARNESS OBSERVABLY DEF
SHIFT SOLENOID CONTROL CIRCUIT OPEN
SHIFT SOLENOID CONTROL CIRCUIT SHORT TO GROUND
SOLENOID AND HARNESS DEF (SOLENOID CONTROL CKT)
TRANSMISSION RELAY OUTPUT CIRCUIT OPEN
TRANSMISSION RELAY OUTPUT CIRCUIT SHORTED TO GND
PCM DEF (3-4 SOLENOID/TRANSMISSION)
PCM DEF (TRANS 3-4 SOL/TRANS RLY CKT)
POWERTRAIN CONTROL MODULE DEFECTIVE
POWERTRAIN CONTROL MODULE DEFECTIVE
POWERTRAIN CONTROL MODULE DEFECTIVE
SOLENOID AND HARNESS DEF (SOLENOID PACK CONN)
TEST COMPLETE
TRANSMISSION CONTROL RELAY DEFECTIVE
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