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How Does a Neutral Safety Switch Work?

A neutral safety switch is pictured in a car.

One lesser known but very important component found on all modern cars is the neutral safety switch. Electrical in nature, but mechanically controlled, this switch keeps your vehicle from starting while the transmission is in gear. It’s important — think of the surprise and possible serious damage that would occur if your car started and immediately went into reverse! With the rise in popularity of remote start systems, knowing that your vehicle won’t go off on its own adventure without you is important. Read on to learn more about what the neutral safety switch does, how it does it and what to do if it fails.

On The Safe Side

Neutral safety switches weren’t always included in passenger vehicles, but they are now mandated. They keep children left alone in the car from starting it up in gear, prevent the car from moving suddenly if started while in gear, and also guard against similar surprises after accidents. The switch is basically a relay — it receives a constant power source when the key is in the on position. When the key is cranked to the start position, it sends that current down a pathway to the starter motor. This pathway is only available, however, if the gear is in neutral or park. Otherwise the pathway is open, and no current can pass.

You may be surprised to learn that a starter motor has more than enough power to rotate not only your engine, but also the entire drivetrain. Turning the ignition key on a car with a manual transmission that is in gear will cause an immediate “leap” into motion without a neutral safety switch to keep things in check.

Where Is The Neutral Safety Switch Located?

On an automatic transmission, the switch is often mounted to the side of the transmission itself, connected to the shifting linkage. It can also be located on the steering column on older vehicles with column shifter. Some modern electronic transmissions without a traditional shifter linkage (shift by wire) use a transmission position sensor (either internal or external) which also serves as a neutral safety switch. The switch is connected in such a way that any transmission shifter location that places it in gear will interrupt the starting sequence. This is what tells it when the proper conditions are met to send current.

On manual transmissions, there’s a switch with a similar function on the clutch linkage typically near the clutch pedal itself called the clutch safety switch. Depressing the clutch pedal allows for the vehicle to start because if the clutch is pushed in, the transmission is now disconnected from the engine.

Bad Neutral Safety Switch Symptoms

How Does a Neutral Safety Switch Work?

A broken or failing neutral safety switch can cause a myriad of problems. If your engine only starts in neutral, but not park, or only park, but not neutral, this could be the culprit. Likewise, if the car starts in all gears, the problem is likely switch related — and a safety concern, so get it taken care of right away. Another warning sign is having to jiggle or slightly move the shifter to get the engine to turn over. There could be something loose in the linkage or switch, and moving it is particularly dangerous as you risk throwing the car into gear while starting it. A bad neutral safety switch can also cause the vehicle to not start at all regardless of which gear it is in.

Going Forward

Neutral safety switches can fail because of age, accumulated dirt, corrosion (one more reason to clean that undercarriage) or damage to the wiring. So long as you don’t have to trace a wire to locate the damaged spot, the switches themselves are easy enough to identify and change. If the neutral safety switch has gone bad, under no circumstances should it ever be bypassed. It is far too easy to let a temporary “get it home” fix be forgotten, often with disastrous results later on. Most neutral safety switches are easy to access and easy to source, so there is no excuse for not fixing it quickly.

Before attempting to start the car back up after making repairs, make sure the vehicle is lifted safely off the ground or that you are inside with a foot near the brake and no one standing around the vehicle. Under no circumstances should you try to adjust the gear or linkage with the engine running while you are underneath. Also, before changing the switch, make sure you’ve ruled out a bad starter, bad selector, dash cluster or other problem with the shift linkage or transmission itself.

These switches are just another one of the many bells and whistles on modern vehicles that contribute to more safety for everyone on the road. If you suspect failure, do yourself and everyone else a favor and drive on over to your local NAPA AutoCare expert to get it checked out.

Check out all the relays, sensors and switches available on NAPAOnline or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on the neutral safety switch, chat with a knowledgeable expert at your local NAPA Auto Parts store.

Photos courtesy of Blair Lampe.

Blair Lampe View All

Blair Lampe is a New York-based professional mechanic, blogger, theater technician, and speechwriter.  In her downtime she enjoys backpacking wherever her boots will carry her, rock climbing, experimental theatre, a crisp rosé , and showering love on her 2001 Sierra truck.

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