by John McCaslin
Drivers with a Freightliner truck with a diesel engine may occasionally see the (Diesel Exhaust Fluid) DEF warning light come on. This light tells the driver that the DEF level is low and must be refilled. While it may be tempting to ignore or reset the light without filling up the DEF, doing so can result in costly repairs. In this blog post, we will explore how to reset the Freightliner Truck DEF warning light and why keeping the DEF level topped off is important.
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What is the DEF Warning Light?
![Def Warning Light Reset Freightliner [Step by Step Guide] (1)](https://i0.wp.com/warninglights.net/wp-content/uploads/2022/11/What-is-the-DEF-Warning-Light.jpg "Def Warning Light Reset Freightliner [Step by Step Guide] (1)")
The DEF Warning Light is a dashboard light in newer model Freightliner trucks that illuminates when the truck’s diesel exhaust fluid (DEF) level is low. The DEF is used to help reduce emissions from the truck’s engine, and when it runs low, the warning light will come on as a reminder to refill the tank.
If the DEF Warning Light comes on, you must immediately add DEF to the tank. You can purchase DEF at most truck stops or auto parts stores. Be sure to use only fresh, undamaged containers of DEF, and do not mix it with any other fluids. Once you add DEF to the tank, the light should reset and turn off.
Why is DEF Warning Light Important on a Truck?
The DEF Warning Light is one of the most important lights on a truck. It indicates when the truck’s diesel exhaust fluid (DEF) level is low. This is a very important fluid that helps reduce truck emissions. When the light comes on, the truck needs more DEF.
Without enough DEF, the truck will not be able to run as efficiently and may produce more emissions than normal. This can be harmful to both the environment and the truck’s engine. That’s why it’s important to keep an eye on the DEF Warning Light and ensure the truck always has enough DEF.
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How to Reset the DEF Warning Light
![Def Warning Light Reset Freightliner [Step by Step Guide] (2)](https://i0.wp.com/warninglights.net/wp-content/uploads/2022/11/How-to-Reset-the-DEF-Warning-Light.jpg "Def Warning Light Reset Freightliner [Step by Step Guide] (2)")
If your Freightliner has a diesel particulate filter (DPF) system, you may see a DEF warning light on your dash. This indicates that the system is not working properly and needs to be reset.
Here’s how to do a Freightliner truck DEF warning light reset:
- Park your truck in a safe place and turn off the engine.
- Remove the key from the ignition.
- Press and hold the reset button on the dash for 5 seconds.
- Start the engine and check if the light is still on. If it is, repeat steps 3-4 until the light goes off.
If you have a Freightliner truck with a DEF warning light, it’s important to know how to reset it. Otherwise, you could end up with an unexpected repair bill. Luckily, resetting the DEF warning light is a relatively simple process that can be done in just a few minutes. So, if you’re having trouble with your Freightliner truck’s DEF system, check out our article on resetting the DEF warning light. We hope this information helps you get your truck back on the road and avoid costly repairs.
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FAQs About Def Warning Light Reset Freightliner
What does it mean when the DEF light is flashing on a Freightliner?
When a DEF indicator light is flashing or blinking, it indicates that the DEF level is critically low. Refilling the tank should be done immediately to avoid any consequences that may arise from ignoring this warning. The utmost importance should be placed on filling the DEF tank promptly and efficiently to continue the vehicle operation safely.
What does a flashing DEF light mean on a 2014 Freightliner M2?
When the DEF Lamp and Solid Check Engine Lamp are flashing, the DEF level is critically low, an incorrect type of DEF is being used, or an SCR system issue has been present for over five hours. If this occurs, a driver should expect to experience a severe loss of engine power. It is important to address these issues immediately to avoid further damage.
Why is the DEF light flashing?
A flashing DEF Lamp signals that the DEF level is below a certain threshold and needs replenishment. To restore the system’s proper functioning, it is necessary to refill the DEF tank. Additionally, when an onboard diagnostics (OBD) detects an issue with the emissions control system, it will cause the Malfunction Indicator Light (MIL) to illuminate. Reaching out to a qualified technician for assistance can help identify and remedy any underlying issues.
What causes your DEF warning light to switch on?
The DEF Lamp is used to notify the driver when the DEF tank needs refilling. When lit, it signals that the DEF level is low and requires attention. A flashing light indicates that the level has fallen below a critical threshold and must be addressed immediately. Refilling the tank is necessary in both instances to correct this issue.
What happens if the DEF sensor goes bad?
Thomas commented on the potential DEF Quality Sensors (DEFQS) malfunction, which can lead to an engine torque derate due to various failure modes. These include incorrect or inappropriate detection of low fluid quality in the diesel exhaust fluid tank, inability to communicate with the ECM, and being in a failed or offline state.
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