The neutral safety switch is a component that is found on automatic transmissions, CVTs, and most modern manual transmissions that, in part, keeps the engine from being started when the gear selecter is in a position that would cause the car to suddenly move forward when starting. Sometimes it works in conjunction with the brake switch so that the brake pedal needs to be pressed in order to allow a shift from park. On vehicles that are started with a key in the ignition, it will prevent the key from accidentally (or intentionally) being removed while a forward or reverse gear is selected.
Transmission Range Sensors
A transmission range sensor is a more advanced version of a neutral safety switch, and are often used interchangably. However, not all neutral safety switches can be considered a range sensor, while the transmission range sensors practically always qualify as a neutral safety switch.
What Does a Neutral Safety Switch Do?
Simply put, if the switch isn't in the right position, the engine won't start. However, as the name may suggest, it doesn't actually perform anything vital to the function of the vehicle, but does play a role in safety.
The switch connects and/or disconnects (depending on the model) electrical circuits that either directly turn on/off components that prevent the engine from being started, as well as keep the gear selector from moving into unsafe positions on some models. Neutral and park are the positions that complete a circuit that allows the engine to be started.
Signs of a Bad Neutral Safety Switch
A malfunctioning neutral safety switch may prevent the vehicle from starting (even when the gear selector is in the correct spot), but you still may be able to get the engine to start by pushing the gear selector "further" into park (if park is all the way forward, putting some force more forward, even though there isn't another option beyond park, is what this means) may give you a few extra starts before the switch fails completely. Selecting neutral when park doesn't work may also get the neutral safety switch to allow another few start-ups, but in both of these cases, the switch is failing and needs to be replaced.
Sometimes, a neutral safety switch will just fail completely, and none of the techniques already mentioned will provide an extra start of diagnosis aid.
In vehicles with a key instead of push button start, you sometimes won’t be able to pull the key out of the ignition, in addition to the no-start issue. Your car won’t let you remove the key if a gear is selected. That is to prevent it from rolling away if you forget to put it in park. If the switch is bad, it will probably keep the key locked in the ignition since the car thinks it’s in gear. If your vehicle has both of these symptoms, your issue is very likely a faulty neutral safety switch. If it’s only exhibiting one or the other, a bad switch is still likely to be the culprit.
When the switch is broken, the car doesn't know what gear you are in, and won't start up.
What Does a Neutral Safety Switch Look Like?
There are two main designs you will usually find, a selector array and a ball switch.
Selector Style Neutral Safety Switch
Selector array style neutral safety switches are typically a flat plastic casing with a metal assembly that allows it to be bolted to the transmission housing. A selector shaft that rotates as the gear selector moves passes through the switch, and the shaft is keyed so that it can rotate a sleeve. That sleeve rotates contacts inside that activate or deactivate, depending on the design. On a neutral safety switch, park and neutral are active, while on a transmission range sensor, multiple signals are available to tell the ECU.
This style of switch can be simply a neutral safety switch or a transmission range sensor.
These are typically bolted to the transmission wherever the selector shaft happens to be.
Ball Style Neutral Safety Switch
A ball style neutral safety switch is a small metal-threaded switch that has a spring pressing on a metal ball to keep it off the actual switch component inside, which will differ in design but since that isn't exposed, they generally look the same. A plug reciever, usually made out of plastic, will almost always be on the opposite side of the ball. If the switch has two or more contacts, it more than likely has an electrical ground connection running through one of them. If there is just one contact, then the metal body of the part serves as the connection to ground.
This design is too simple to be a transmission range sensor, as it can only provide on/off data. Multiple of these can do the job of a transmission range sensor, but this approach isn't used often on personal vehicles.
These are threaded into the transmission.