See Why the Shifter Gets Stuck in Park
On cars from the Seventies you could grab the shifter and pull it out of park without having the keys in the ignition or your foot on the brake. In 1992 the Government stepped in to stop the madness and required car makers to install an ignition park interlock. This would stop children from getting into trouble if the parents took the keys out of the car.
Fast forward a few decades and now we have a park brake interlock system. It’s hard to disagree that having your foot on the brake pedal when shifting out of the park position makes a lot of sense. That is until you apply the brake pedal and the interlock malfunctions leaving you stuck in the driveway. Here we will discuss a brief history of the system, how it works and review solutions to common problems.
Park Lock History
Even though the park brake interlock system has been around since the eighties it wasn’t mandated by the U.S. Government until 2007. Of course by this time most car companies where already using it on a voluntary basis. Mazda rolled it out in the early nineties. General Motors and Ford had it on most models by 1996. The last American car company to jump on board was Chrysler. It wasn’t until early in 2000 when they made it standard equipment across their entire car line.
Park Brake Interlock Operation
The scary days of your child being able to rip the shifter out of park while you’re in the convenience store are long gone. Now on all vehicles built since 2007 the electronic shift lock release system will prevent this from happening. The interlock provides several redundant safety backups by first, not allowing the ignition key to be removed unless the shifter is firmly in park. Next it will prevent movement of the shifter unless the ignition key is in the on or run position. The icing on the cake is that the brake pedal will also need to be applied before the shifter is released.
On the earliest systems from the 90s, a cable was used to operate a manual lock mechanism. As time went on a hybrid system came out where the cable operated a solenoid responsible for locking the shifter. On newer vehicles the solenoid is triggered by an electrical signal received when the brake is applied and the ignition switch is on. Therefore the system deployed on your personal vehicle will fall into one of these categories which can be important for diagnosis.
Park Interlock System Problems
Since most vehicles built in the last decade use an electronic version of the park brake interlock system, battery and charging malfunctions are capable of causing issues. If a depleted battery contains less than 9 V of charge there may not be enough electrical power to release the spring loaded lock. Due to the location of the solenoid near the shifter mechanism, drivers can sometimes hear a buzzing sound when this type of malfunction occurs. Either charging the battery or jump starting the automobile can correct the condition.
On many models, car manufacturers will use the rear brake light switch as an input signal to energize the lock release solenoid. When the shifter becomes stuck in the park position, push down on the pedal and see if all the brake lights come on. If they do not, you could have a miss adjusted switch or problem with the circuit itself. Correcting this condition will be necessary in order to get the park brake interlock to function again.
Aside from the problems mentioned above the shift lock system is relatively simple and therefore fairly reliable. As a mechanic I can say that when I run into problems where the shifter is sticking in park it often leads back to a human malfunction. Since the safety lock solenoid is located in the center console on floor shift models it is also susceptible to the common problem of spilled drinks.
Almost all center consoles have a cup holder. This is often located directly behind the shifter. Spilled drinks containing sugar, especially coffee and soda, can work their way down into the solenoid and cause a binding condition. As a sugary drink dries it can form a very strong sticky glue like substance that can prevent the park lock from releasing.