Thursday, October 19, 2017 Detailed Auto Topics
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Most modern vehicles will not shift out of the park position, unless we apply the brakes. This is a safety feature.  The feature may go unnoticed, until the vehicle will not come out of park, even with the brakes applied. In the past, they equipped most vehicles with a manual transmission. When parking a manual transmission vehicle, we place the shifter in reverse. Because the gears in this transmission physically engage each other, this keeps the vehicle from rolling.

Today they equip most vehicles with an automatic transmission. With an automatic transmission, fluid pressure applies the gears. When the engine is not running, pressure drops to zero. Without the engine running, an automatic transmission turns freely, though it may be in gear. To solve the problem, engineers use a parking mechanism.

A basic transmission parking mechanism

When we shift into park position, the parking pawl engages a parking gear. They attach this parking gear to the output shaft of the transmission. This physically locks the output shaft to the case of the transmission and prevents the vehicle from rolling. Selecting any gear, other than the park position, releases the mechanism.

Problems from parking on an incline

The park system is simple and robust, but problems can occur. One such problem is a shifter that will not come out of the park position. The most common cause is the brake/shift interlock, discussed in the next section. Another cause is too much force applied by the park gear.

Parking on an incline can cause the parking mechanism to stick 

Parking on an incline may cause our shifter to stick in the park position. If we release our brakes, after we shift into park position, the vehicle may roll. This places the weight of the vehicle on the parking gear and pawl. With too much load on the system, we cannot shift from the park position.

When parking on an incline, we first firmly apply the parking brake. Before shifting to park, we take our foot off the brake pedal and make sure the vehicle does not roll. With the vehicle weight held by the parking brake, we shift into the park position. With this method, the parking brake holds the weight of the vehicle and not the park pawl and gear. We can easily move our shifter out of park position.

If the shifter will not come out of park position, due to the vehicle rolling, we need to push it slightly, to relieve the pressure. Moving the vehicle uphill takes the weight off the transmission. If the incline is slight, we may move it by hand. Be sure to apply the brakes firmly, before taking it out of the park position. On larger inclines, we may need a wrecker or push-vehicle. Only a few inches will normally relieve the pressure.

Never try to force the shifter

We should never try to force the shifter to move, when it sticks in park position.  If normal effort does not move the shifter from the park position, pulling with more force will not help and will likely break something.  Most shift mechanisms use a cable to connect to the transmission. They construct shifter cables and mechanisms of light materials. Any excessive force will break the cable or damage the shifter. If the shifter cable breaks, changing gears is not possible. Repair involves towing the vehicle and replacement of the shifter components.

The brake/shifter interlock

Accidently shifting a running vehicle into reverse or drive could be devastating. Over the years many people have been injured and property damaged by this exact occurrence. The brake-shift interlock is designed to prevent the vehicle from being shifted out of park, without the brakes being applied.

The shift/brake interlock keeps the shifter in park

Engineers have designed many different systems, but they all require brake application to release the shifter from the park position. Most systems use a magnetic solenoid or an actuator that blocks the path of the shifter. Applying the brakes sends a signal to the mechanism which releases the shifter. Things sometimes go wrong and the vehicle may not allow the shifter to move from the park position.

Examples of problems include the mechanism failing in the locked position and the brake light switch not sending the signal. Such failures keep the shifter from moving out of the park position.

Because failure will strand the driver, they usually provide means to override the system. The override feature allows the driver to release the shifter in an emergency. Each vehicle uses a different procedure making it difficult to remember how they all work.

Finding the release procedure

Fortunately, they will normally outline the procedure in the owner’s manual. Finding this information and practicing the procedure, before the need arises, is a wise precaution. In an emergency, attempting to find this information will be far more difficult.

A few common methods to
override the shift lock

General Motor column shifter 

with the key in the right position some column shifters can be moved to neutral

With many column-mounted shifters turning the key to the first position after lock may allow overriding the system. The key must stop in position one. Turning the key all the way to on position will lock the shifter. Normally in the first position the dash will not light up, but the shift indicator may be on.

With the key in this position, apply the brakes and shift the vehicle to neutral. In neutral the vehicle will start and we can shift to drive or reverse. This allows the vehicle to override the shift-lock, but it may again lock when shifted back to park.

Ford column shifter

some Fords have an access slot under the column to override shift lock

If turning the key to the first position does not work, there are normally other methods.  Check carefully around the steering column for an opening. Some Ford column shift vehicles have a slot, under the column. Pushing a key or a screwdriver into the slot releases the brake-shift interlock.  Apply the brakes and push on the release.  The vehicle should shift out of park.

Honda Odyssey column shift

Shift brake over ride on Honda Odyssey

The Honda Odyssey, with a column shift, provides a small access slot on top of the steering column. This small cover can be very hard to see and most people never notice it. Carefully prying up, with a very thin item, such as a pin knife, removes the plug.

Releasing Honda Odyssey stuck in park

After removing the plug, push down with something such as the ignition key. This moves the release mechanism and we can shift to neutral and start the engine. Once started, shift to drive or reverse. Returning the shifter to the park position will lock it. Repeat the process to release the shifter again.

Console mounted shifters

many console shifters have a small plug for access to shift lock override

Console type shifters often have a small access plug, that may be removed.  Removing the plug allows a person to reach the brake-shift interlock override. With the plug removed, push down on the mechanism to allow the vehicle to be shifted out of park.  Other models use a release button or a small access slot. The button overrides the brake-shift interlock when needed, and they often label them. On a vehicle with a release slot, pushing the key into the opening releases the shifter.

Different vehicles use various methods to override brake-shift lock

They place the access plugs in various locations, depending on the vehicle. Many are above, to one side or even below the shifter. The plug may also be found on the side of the shifter plate, on a few models. On other vehicles we pull the shifter bezel from the console and the release is below the cover, on the side of the shifter. 

A little time spent learning where the brake-shift interlock override is and how it works can prevent a great deal of trouble. If it cannot be found, check with your favorite mechanic. They will normally be happy to help.





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