What Does The Blue Light Mean On A Car Dashboard?


Dashboards contain all sorts of lights and signals that tell us what’s going on. You might see a light that indicates your headlights are on, a light for your seatbelt being unbuckled, or even an indicator light for low fuel. No matter what light is lit up, they’re there for us to determine if and when something needs to be addressed.

Have you asked yourself, “What does the blue light mean on a car?” Blue lights on a dashboard can mean a lot of different things. In some cars, blue light could mean that the high beams are on. Most cars have a blue light that correlates with the temperature of the coolant.

Just like a red coolant thermometer means that the coolant is too hot, a blue thermometer indicates the coolant is too cold. Coolant helps the engine to stay cool, so this might seem counterintuitive. At the same time, coolant that is too cold indicates your engine is too cold to start. These are important signs to pay attention to when you see them.

How does the blue coolant warning light work?

So what does the blue light mean on a car? The answer lies in first understanding how the coolant temperature light works. Your engine doesn’t produce thermal energy when it’s parked. It might continue to produce some residual heat as it cools down after driving it, but the source of energy has been cut off.

Coolant is the liquid that keeps your engine from turning into a fiery ball of hot metal. Depending on the design of the engine, the coolant moves in different ways across certain metal components to take away the heat and redirect it. This allows for a semi-constant temperature that’s ideal for operation.

In the summer, your engine maintains a higher temperature, just like your body. It’s simply a response to the environment. In the winter, the engine, like any metal, is much colder. The coolant thermometer is what indicates the temperature of that liquid.

A red coolant temperature light means the coolant is very hot. It’s not cooling the engine down as it should and so your engine is now at risk of overheating, failure, and potentially starting on fire. The opposite is true for a blue coolant temperature light. This means the coolant is too cold to optimally regulate the temperature of your car’s engine.

What are the reasons the blue coolant light comes on?

Under normal driving conditions, the blue coolant light comes on as an indication that the coolant, and therefore the engine, is not up to optimal operating temperature. If you’ve ever driven a diesel, it’s similar to the glow plugs requiring heat before the engine can fire.

However, there are several reasons the blue lights may come on to indicate failure of some kind. In these instances, the indicator light may not match up with the situation at hand. When this happens, it’s time to look for leaks, faults, or issues with your coolant pump.


Most often when your coolant leaks, it causes the engine to overheat. However, leaking coolant can also potentially cause the blue coolant light to come on. If water were to get into the system and freeze, it could potentially both bring the coolant temperature down and cause a leak in the radiator, hoses, or couplings at any point in the system.

You’ll know a coolant leak by the smell. Coolant has a sweet smell to it that’s different from any other smell associated with a car. You can also identify coolant by the neon yellow/green color it often has, depending on the type of coolant you use.

Sensor faults

A blue coolant light can also be the cause of a sensor fault. If a sensor were to give the improper reading, it could cause other parts of the system to malfunction, even though they’re operating properly based on the information they receive. It’s similar to your engine thinking it has more air than it does and adjusting the air/fuel mixture wrongly.

Sensors are a good place to look first, as they are what directly turn on the blue coolant light. If you can’t find a leak and the sensors are working properly, chances are it’s going to be your coolant pump.

Pump issues

The coolant pump is what drives the cooling liquid through the system. Failing pumps can cause issues with flow, which may end up influencing the sensors and even causing leaks under the right conditions. If you have a blue coolant light on and aren’t sure what the culprit is, check the coolant pump for issues as well.

What to do when the blue coolant light comes on?

The second question to “What does the blue light mean on a car?” is “What do I do when the blue coolant light comes on?” The first step is diagnosing the situation. If you’ve just gotten into your car and the temperature outside is not only below freezing but also below 0 degrees Fahrenheit, it’s no wonder the blue light is on.

Chances are if your coolant temperature is so low that the blue light is coming on, the engine is too cold to start. It’s not a matter of cooling the engine down anymore. It’s a matter of the internal components being unable to operate in such conditions.

You might compare it to the body when it comes to extreme temperatures. Your heart needs heat and blood flow to keep beating. When temperatures get too far out of the normal bounds, systems go haywire. The same can be said for your engine.

The best thing to do when the blue coolant light comes on is to wait. This might mean waiting a few minutes until the engine heats up or waiting several hours or even days until the weather warms up. If you can get the vehicle into an area where you can warm it up manually, that works as well, but you’ll have to do it without turning the engine over.

Can you drive with the blue coolant light on?

If you are already driving and underway when the blue coolant light comes on, you need to assess the situation. When conditions exist that warrant such a response from your vehicle (such as freezing temperatures), this might just mean it’s cold outside. If the car has been running long enough to warm up the engine, this is an indication that you need to get where you’re going quickly or risk damaging the engine irreparably.

Should the blue coolant light come on when it’s the middle of summer and there’s not a drop of cold moisture in sight, this indicates a failure of some kind. As we discussed, it could be a leak, a sensor failure, or even an issue with the coolant pump. The temperature readings are inaccurate, which could lead to further issues if left unchecked.

For example, if for whatever reason the coolant temperature is above what it should be normally and it’s not reading properly on the sensor, you could have an engine close to overheating. If you don’t know what your coolant temperature is, you don’t know if the engine is at the optimal temperature or not. The best course of action is to turn the car off and call a mechanic.