A neutral safety switch is pictured in a car.

How Does a Neutral Safety Switch Work?

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 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! 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 mandated. They keep children left alone in the car from starting it up 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. On an automatic transmission, the switch is often mounted to the side of the transmission itself, connected to the shifting linkage. 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, called the clutch safety switch.

Neutral GroundHow 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.

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.

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 selector, dash cluster or other problem with the 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 NAPA Online or trust one of our 16,000 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.

about author

Blair Lampe

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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