Freightliner Cascadia / Detroit DD13, DD15, DD16 & Cummins ISX etc. FAQs

Here are some common causes of inaccurate or erratic DEF level gauge readings on a Freightliner Cascadia truck with a Detroit DD15 engine: Actually low DEF fluid level: This may seem obvious, but if you're running low on DEF, it can cause issues. This is the most common cause of inaccurate or erratic DEF level gauge readings. If the DEF fluid level is low, the gauge or dipstick may not accurately reflect the actual DEF level. Faulty DEF level sensor (aka DEF sending unit): If the DEF level sensor or wiring is not functioning properly, it may not accurately detect the DEF fluid level and the vehicle's computer system may not display the correct DEF level on the dashboard gauge or dipstick. This can cause the DEF level to fluctuate or appear to be erratic. The DEF level sensor is part of a multi-purpose component that also includes the DEF quality sensor, DEF tank temperature sensor, and DEF tank heater. Please note that if you are seeing DEF fault codes for any of these components, you may have a malfunctioning DEF sending unit (aka header), which is mounted on top of the DEF tank and looks like a cap with a clamp, but has tubes and wiring that goes down into the tank.

Make sure the parking brake is set, hood is latched, transmission in neutral Turn the ignition on or start the engine Double tap the button with the 2 squares icon (on the right hand side of the steering wheel) Follow the prompt to enable “interior comfort”, by pressing the right arrow to switch to “on” and press the OK button A green engine with an arrow wrapped around it will appear, informing you that the truck is in optimized idle and it will start / shut down as necessary to keep the temperature at the setting of your choice, also based on battery voltage, ambient temperature etc.

Remove the access cover for the clutch, if applicable Bar the engine over with a barring tool, or by the alternator (not recommended), until you find a bolt head placed in the middle of a tab (this is the adjustment bolt) Place the correct socket onto the bolt with a ratchet, afterward, press on the ratchet with a pry bar in order to press the bolt head in and begin turning clockwise Begin with 1 full turn and check your adjustment Repeat steps 3 and 4 as necessary