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Understanding Semi-Truck Dashboard Warning Lights!

Understanding the semi-truck dashboard warning lights is essential if you know your truck has issues. They can spot potential problems and help you stay on top of routine maintenance.

There seem to be more and more warning lights as technology advances. But each warning light illuminates for a reason when your semi requires attention.

The symbols and dash location of warning lights vary depending on the age and model of a semi. To give you a general idea, however, below are the most common warning lights you see in most semi-trucks.

Engine Warning/Check

All semi-trucks have a “check engine” light. This warning light means the engine has performed a self-diagnostics check and is producing a fault code. If another warning light accompanies this light, you will have a better idea of the fault. If the Check engine light alone is on, a qualified mechanic will need to run a diagnostics check to find the fault.

Fuel Gauge

There’s no mistaking the fuel warning light. It’s usually going to be a picture of a fuel pump next to your fuel gauge, or you’ll also have a light on your gauge.

It’s so crucial that you do not run out of fuel that this warning light sometimes comes with an alarm sound, too. The fuel warning light is set to come on long in advance of you running out of fuel. It varies across different brands, but generally speaking, the light will pop up when your tank is running low. Still, you should always fill up your tank well in advance of the fuel warning light coming on. One consequence of continuing to run your engine on low fuel is that the it will be forced to pick up the sludge and sediment that settles at the bottom of the fuel tank. Potentially causing unnecessary and preventable damage.

Engine Oil Pressure

Seeing an oil pressure warning light appear is cause for concern. Remain calm and stop the truck as soon as possible to figure out why the light is on. The most common reason for an oil pressure light coming on is to indicate the engine oil level is too low. Hopefully, simply topping off the oil will resolve this. However, it could indicate the oil is too low or high in viscosity. It may even be a sign that the engine shows signs of wear or that your truck needs a oil change.

Engine Oil Level

Having sufficient levels of the correct oil in your engine is essential to keep an engine running smoothly and maximize the truck’s life. If a warning light comes on indicating loss of oil pressure or your engine oil is low, you will need to top it off as soon as possible. It may mean you have a leak, although engine oil does burn off over time and needs topping up.

Coolant Level

If a temperature warning light comes on indicating your engine coolant level is too low, you need to get this looked at as soon as possible. If you can’t stop anytime soon, keep an eye on your temperature gauge for any sign of overheating. Coolant is the liquid that flows around the truck’s engine to keep it cool. If it’s low, there is a risk of the engine overheating. This can lead to permanent engine damage.

Your coolant level can lower over time, but you may have a leak.

Brake Pressure/ABS

Semi-trucks use air brakes and ABS (anti-lock braking system). These are sophisticated braking systems, and they help heavy vehicles greatly reduce their braking distance.

If you have a warning light indicating a problem with your braking system, you need to get it looked at as a matter of priority. Bad brakes potentially put you and other road users’ lives at risk.

Tire Pressure

Newer semi-trucks have tire pressure monitoring systems (TPMS) to let you know when one or more of your tires are low on air pressure. Sometimes the tire pressure light will come on, but there’s no indication, such as a blowout. It’s a warning that the pressure may have dropped below the recommended minimum. You should check the pressure in your tires at your earliest convenience. Underinflated tires are at greater risk of failing. Moreover, they also lead to fuel usage increases.

Voltage Warning

There are often one of two warning lights relating to the status of your battery. Some models will have a warning light if a battery is not sufficiently charging and may have a different light to indicate an electrical fault. If your battery is not sufficiently charging, it’s only a matter of time before it will fail to start. One possible culprit of a failing battery could be the alternator. The alternator is a electric generator in your vehicle used to charge the battery and power the electrical system while the engine is running. Another possibility is that your battery’s life is simply approaching its end.

Airbags and Seatbelts

Airbags and seatbelts are two of the essential safety features that will protect you in the event of a collision. If either of these warning lights on a semi-truck is on, you should make it a priority to have it checked.

Transmission Warning

There will be one or more warning lights relating to the transmission in your truck. The most common transmission problems are low fluid or pressure or the temperature rising too high.

Similarly, it’s another warning that needs attention as soon as possible.


As you can see from the above information, understanding the dashboard warning lights on a semi-truck is important to ensure you and other road users are safe. Not only that, ignoring semi-truck warning lights can prove costly if the fault worsens. When you need semi-truck serious, contact Road Hammer Repair 734-250-7032.

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