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The article will demonstrate how to replace a Mercedes' DEF tank, heater, and pump. Although the pictures are from a 2010 Sprinter, the procedure is similar for Mercedes R350, ML350, GL350, E350, S350 diesel with BlueTec technology.  

Table of Contents

If you are the owner of a diesel Mercedes-Benz BlueTec, one day, you may be greeted with the check engine light often triggered by a fault code such as 20BE1B, 20BD1B, P20B8, P20E8, P20BD, P20BE, P20B9.

These codes are typically due to a faulty Mercedes Diesel Exhaust Fluid (DEF) heater or DEF pump.

What you will need


  1. Park the Mercedes on level ground and let it cool down.
  2. Locate the DEF tank. On Sprinter vans, it is below the sliding door on the passenger side. On a limited number of models, the BlueTec tank is located in the trunk or engine bay.
  3. Remove two brackets that hold the DEF tank secured to the body. remove mercedes adblue tank heater
  4. Have a helper keep the DEF tank up while you disconnect all the hoses and wires from the tank. mercedes adblue tank heater replacement
  5. Remove the DEF tank from the car and disconnect all the electrical connectors and hoses from the DEF heater and pump.mercedes adblue pump failure
  6. Remove all 4mm hex bolts that secure the pump to the DEF heater. mercedes reductant heater
  7. Remove the DEF pump from the DEF tank (top of the DEF heater). Remove the large locking ring from the DEF heater element.remove sprinter def heater
  8. Remove the DEF heater element from the tank.mercedes ml350 def heaterTo disconnect the inner heater part from the tank, you will slide your hands inside the tank and slide the plastic counter-clockwise.remove mb heater

    Mercedes DEF tank removed.

    mercedes ml350 def heater
  9. Install the DEF pump and heater element. 2012 mercedes sprinter def heaterSeveral O rings will most likely come with your new DEF pump. Make sure to replace them, including the one that connects the pump to the heater element.2011 mercedes sprinter 2500 def heater
  10. Tighten the lid locking ring. Make sure the mark on the ring matches the ring line up on the tank mark.
  11. Install the DEF tank on the vehicle. Add DEF fluid to the top of the tank.mb def heater
  12. Lastly, use an OBD2 scanner to clear the check engine light. You could potentially drive the vehicle, and the CEL will clear on its own if the problem is no longer present. Our recommendation is to clear the code with a Mercedes Star Diagnostic scanner then monitor to make sure the CEL doesn't return.

If your Mercedes BlueTec check engine light is on with a fault code related to the DEF heater, you need to get it fixed as soon as possible. Otherwise, when you ignore the CEL, your Mercedes may go into limp mode, and also, you may start to get a warning message on the dashboard stating " x starts remaining," after which point you will no longer be able to start the car, van or SUV.

If you are having problems with your DEF system, including the heater element, our recommendation is to call a Mercedes-Benz dealership near you and check any open recalls. If there is an open recall, your dealer will fix the problem under warranty. A Federal mandatory warranty covers all emissions issues up to 80,000.

You may have been quoted to replace the DEF tank, heater, and pump altogether, which at the dealer can cost as much as $4000. Replacing the DEF tank is rarely necessary unless it has developed a crack.

Mercedes DEF Heater Part Numbers

Verify your Mercedes DEF heater part number with the seller or by calling your dealer.

If the Mercedes is out of warranty, you have a couple of options.

  • To take it to the dealer and spend anywhere from $1800 to $2500 to replace the DEF heater.
  • Second, you can purchase a new Mercedes DEF heater online and replace it yourself in less than two hours.

Why does my Mercedes need a DEF Heater?

All DEF systems require heating elements to prevent DEF fluid from freezing at temperatures less than twelve degrees Fahrenheit. DEF Heating Pots are designed to quickly return DEF to liquid form, ensuring proper flow through the lines and pump unit. If your diesel vehicle is operating in limp mode or is not operating at full power, a common culprit is a failed DEF heating element.

DEF heater is also known as the DEF, Diesel Exhaust Fluid Heater, DNOX Heating Unit, Urea Tank, Adblue Preheater Module.

Related Terms

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Mercedes sprinter def heater Mercedes def tank heater Mercedes gl350 def heater Mercedes ml350 def heater 2013 Mercedes sprinter def heater 2012 Mercedes sprinter def heater Mercedes sprinter def tank heater

Mercedes 20BD1B Code

  • The output for the heating element AdBlue tank has an electrical fault or open circuit.