What The Car With A Lock Symbol Means On Your Dash (And 2 Possible Reasons It Won't Turn Off)

These days, every car, truck, and SUV on the road comes equipped with early warning systems designed to help you catch potential issues before they become major problems. Each of those systems has a corresponding warning light that pops up on your dashboard display when an issue does occur. 

It's possible, however, that you may not know what all of those symbols mean. If that's the case, you can use your iPhone to determine the meaning of each, and the smartphone would likely tell you that the in-dash light that looks either like a car with a lock on it or a car with a key inside of it is the immobilizer warning. The symbol may vary depending on the make and model of your vehicle, though they mean exactly the same thing, which is that the immobilizer system on your car has been engaged.

Now that you know what the light means, you might be asking yourself what the immobilizer system is. Put simply, the immobilizer is a passive anti-theft security feature designed either to prevent a vehicle's engine from turning over or to turn it off after a few moments if the correct key is not present. Once the immobilizer is engaged, you'll need to take the correct course of action to shut it off and be able to start your car. Here are a couple of reasons the immobilizer light on your car is on and won't turn off.

Whether you've noticed it or not, the immobilizer light illuminates every time you insert a key into your vehicle's ignition and try to crank the engine. It does not typically stay on, however, shutting off when the engine turns over. Yes, that means the warning light is directly connected to the ignition process, and yes, if you inadvertently put the wrong key into your vehicle's ignition and try to turn on the car, the light stays on to let you know the immobilizer has been engaged. This happens because a coded signal is sent to the key's transponder when it's inserted in the ignition, and if the transponder does not recognize the signal, the immobilizer prevents the engine from turning over. 

The immobilizer system does not immediately turn off once you've removed the incorrect key from the ignition. Rather, some immobilizers and their corresponding warning lights will remain on until you put the correct key into the ignition and try to turn your vehicle on. While that's a simple enough way to disengage what can be a profoundly effective security feature, immobilizers have likely been the cause of a facepalm moment or two for people who do not immediately realize that they're using the wrong car key. 

If you are using the correct car key when the immobilizer is engaged, you might need to replace the key as its transponder chip may be faulty. As I learned when the immobilizer warning light recently came on in my own car, you should still be able to operate the vehicle using a functional backup key if you have one.

Of course, many modern cars with immobilizer systems installed do not use a classic key and ignition starter these days, as key fobs and keyless ignition have become more and more the standard. The digital component involved in the ignition process with key fobs makes it just as easy, if not easier for a vehicle to know if a driver is using the correct key, and when that key is not present in the vehicle, the immobilizer and its in-dash warning light are quick to turn on and terminate engine functions.

However, in cars that use a key fob for ignition, the immobilizer warning light may remain illuminated even if the vehicle turns on and is operational. There are a couple of reasons this may happen, and both indicate that there is likely an issue with your key fob, as the signaling chip installed in that fob could be faulty or the battery powering it may be too weak to send a constant signal to the vehicle's computer. In either of those cases, it is possible that the immobilizer warning light may remain illuminated until the issue has been addressed.

If the problem is a faulty chip in your key fob, you will likely need to visit an automotive professional certified by the vehicle's manufacturer to correct the malfunction, as a diagnostics check may be required and a new key fob may need to be issued. You may also need an auto pro to replace the fob's battery, though it could be possible to perform that change yourself, depending on your vehicle model.