How to Replace the DEF Level Sensor of a Volvo VNL

If your Volvo truck has DEF-related fault codes, engine derates, or an inaccurate DEF level gauge you may want to check the DEF level sensor. Expensive repair? Totally. But by following this step-by-step guide you’ll be able to replace the part yourself and save some precious cash. Let’s dive in.

Tools You’ll Need

Socket set and ratchet
Torque wrench
Screwdrivers
Drain pan
Replacement DEF level sensor
Coolant extractor
Personal protective equipment

Step-by-Step Instructions

1. Prepare the Truck

Park the truck and truck and turn off the engine. It’s important to let it cool down before you do anything.

2. Disconnect the Battery

Disconnect the negative battery cables to prevent electrical shocks.

3. Drain the Coolant and Diesel Exhaust Fluid

Take the drain pan and place it beneath the radiator drain fitting, then use a coolant extractor to drain the coolant from the system. Remove the drain plug from the DEF tank and let the fluid out.

4. Access the DEF level sensor

Remove the left-side fairing under the cab door and you should have easy access to the DEF tank. Take the floor jack and use it to support the DEF tank to prevent it from falling.

5. Disconnect Electrical and Fluid Lines

Now you can disconnect the electrical harness from the Aftertreatment Control Module (ACM) and the DEF level sensor electrical connector. Also, disconnect the DEF level sensor-to-doser valve fluid hose and the coolant lines attached to the DEF tank.

6. Remove the DEF level sensor

Remove the fasteners and secure the DEF tank to the frame-mounted brackets, then lower the DEF tank using the floor jack. Make sure to loosen the clamp that connects the DEF level sensor to the tank and remove the level sensor assembly.

7. Install the New DEF level sensor

Take the new DEF level sensor and put it onto the tank, then attach the clamp. Double-check all connections and make sure they’re free from contamination before installation.

8. Reconnect Electrical and Fluid Lines

Reattach the DEF fluid hoses and coolant lines to the new DEF level sensor. Don’t forget about the electrical harnesses and ACM connectors.

9. Reinstall the DEF Tank

It’s time to lift the DEF tank back onto the support pins on the frame-mounted brackets and secure it with the mounting fasteners.

10. Refill Coolant and DEF

Now you can refill the cooling system with the recommended coolant and the DEF tank with fresh DEF fluid.

11. Reconnect the Battery

Reconnect the negative battery cables and tighten them well.

12. Test the System

Start the engine and check for leaks. You can also use a diagnostic tool to check and clear any diagnostic trouble codes, if necessary.

Conclusion

Replacing the DEF level sensor of a Volvo isn’t easy work, but if you take your time and follow the steps above, you shouldn’t have any problems doing so. Congrats! You saved a couple hundred dollars you’d have spent on a mechanic. Stay safe and keep hauling!