Understanding the Dashboard in a Heavy-duty Truck

Dashboard symbols in semi-trucks

What your dashboard gauges and warning lights are really indicating   

Your next loading dock is 45 minutes away. With a quick glance at the dashboard, you notice the fuel level is low, and the tire inflation light is on. Should you pull over to fuel up and check out the problem or is it safe to continue driving? While some dashboard lights and instruments indicate emergency situations, others notify the driver of issues that could be concerning if they aren’t serviced soon. To keep trucks in normal operating condition, drivers should understand the function of each panel control so they can detect and call in any complications. 

Note: The following gauges and warning lights are on all heavy-duty dashboards. Please refer to the vehicle’s operation manual to learn about controls specific to your truck.

Common truck gauges

Dashboard gauges display vital information and data to keep drivers aware of how the truck and its internal parts are functioning. These include the:


Most drivers are already familiar with the function of the odometer — it displays the total mileage on a truck and can also display mileage data for a specific route. This information helps determine when a vehicle needs an oil change or other maintenance based on mileage.


This dash gauge displays the battery charge status using numbers (12/14/16) or three colored sections. With a numbered voltmeter, a fully charged battery will read 14 to 14.5 volts when the engine is running (and the charging system takes over). Unless there is a heavy pull on the electrical system, it should stay within this range. If the voltage constantly stays below 14 volts (under charged) or goes above 15 volts (over charged), you should have the system checked. With a colored volt gauge, if the needle hovers over the left-hand red area, it means the battery is undercharged. The middle green area means normal battery charge, and the right-hand red area means it’s overcharged. Watching where the needle lands can help drivers anticipate charging issues before they become major problems.


The tachometer measures the engine’s speed in revolutions per minute (RPM). Today’s diesel engines are designed for maximum peak torque at lower RPMs.

Engine oil pressure

This gauge monitors the truck’s oil pressure — normal oil pressure is between 30-70 pounds per square inch (PSI). Inadequate oil pressure can cause engine damage.  

Fuel gauge

Drivers should regularly check the fuel gauge to make sure there’s plenty of diesel to reach the destination.

Air pressure

The air pressure gauge measures the PSI in each truck reservoir. Pay attention to both the primary and secondary gauges — any pressure falling below 90 may indicate leaks or other issues in the air brake system. If this happens, quickly pull over to a safe location before a breakdown or accident occurs.

Temperature gauges:

A heavy-duty truck’s dash features multiple temperature gauges. Some gauges require high temperatures, while others require low temps for best performance capabilities. Locate and familiarize yourself with all temperature gauges, including the: 

  • Coolant. Shows the coolant’s temperature. Average engine temps vary but are usually between 165-195 degrees Fahrenheit. If the coolant is too hot, you should pull over at the next safe location, let it cool down, and check the manual to verify normal temperatures (many heavy diesels have 195 thermostats in them).
  • Engine oil. Displays how hot the motor oil is. Excessively high temps may lead to engine damage.
  • Pyrometer. Monitors the engine exhaust temperature and warns drivers of potential engine damage.
  • Transmission. This gauge indicates the transmission’s temperature. Temp ranges vary per manufacturer — be sure to check the manual to verify normal temps.
  • Rear and forward axles. Tracks how hot the oil in both axles is. During normal operation, forward-rear and rear-rear axle oil temperature gauges should read between 160 to 220°F (71 to 104°C) for Meritor axles, and 80 to 200°F (82 to 93°C) for Dana Spicer drive axles. Under heavy loads, such as when climbing steep grades, temperatures that exceed the normal oil temperature range for a short period of time are not unusual — there’s not an issue as long as the temperature returns to normal when the load decreases. Be sure to check the manual to verify normal temperatures for your specific vehicle.

Dashboard symbols and warning lights

Dashboard warning lights can signal a variety of things — both emergency and non-emergency. Because of this, it’s critical to know what each signal means so you can identify if a warning light needs immediate attention or if the issue can wait. And while the location, color and design of each symbol differ by truck manufacturer, common symbols to be aware of include:

  • Check engine light. An engine light can indicate both minor and major issues. When it comes on, look for other warning signals such as low oil pressure or engine overheating. Then, pull over and power down the vehicle as quickly and safely as possible.
  • Low coolant level. This warning signals low coolant levels. While it doesn’t require immediate attention, the driver should relay this information to the carrier, who can then schedule a maintenance checkup.
  • Tire inflation. Underinflated tires can lead to serious breakdowns or accidents. Anytime this warning signal flashes, the driver should park somewhere safe and manually check each tire’s pressure.
  • Alternator check. This light could mean the alternator isn’t charging the battery correctly. The driver should pull over when possible and only use necessary accessories (like the windshield wipers, headlights, etc.) until the alternator can be checked.

Maintenance Solutions from FleetNet America®

When a gauge malfunctions or a light indicates service needs, trust FleetNet America® to fix the issues and get you back on the road quickly and efficiently. Our fleet maintenance program helps carriers solve whatever maintenance problems they face. Call us at 877-559-9640 or comment below for more information.