Jim Grant's Tech Tips
Unlockable Automatic Transmission Shifter Lock
Q:
The shifter
would not unlock out of park on my car. After following the procedure
in the Owner's Manual, we were able to get it to release. What do you
think the problem is and approx cost?
- Marshall W.
A:
Knowing the year, make
and model of your vehicle would make things a little easier to answer
your question. The shift-inter lock systems are found on most all makes
of vehicles equipped with automatic transmissions. The reason for the
shift-inter lock system is to assure that the driver of the vehicle has
their foot on the brake pedal, not the gas, when moving the transmission
selector from park to drive or reverse. The operating system of the shift-inter
lock is reasonably generic across the line of manufacturers. There will
be fuses, a brake pedal position switch (many times it is the brake light
switch) a possible relay/module and last a solenoid/actuator. When the
ignition is turned on electrical power goes to and activates the solenoid/actuator.
The solenoid will pull a pawl/lock into place that blocks the movement
of the shifter. When you step on the brake pedal another electrical signal
is sent to the relay/module and it responds by canceling the other signal,
which causes the shift-inter lock solenoid to release, allowing the shifter
to be moved. The most common problem we see in the shop are failed fuses
or worn shift-inter lock solenoids. The inside of the solenoid will wear
and bind internally and will not release once activated. The fuses you
can check yourself. Leave diagnosing the rest of the system to a qualified
technician.
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