E350 Bluetec DEF Heater Replacement DIY
Thread Starter
Junior Member
Joined: Oct 2016
Posts: 20
Likes: 0
From: California
2011 E350 Bluetec
Hi all diesel mechanics out there.
Skipping the often asked stuff about DEF, Adblue or whatever kind of 33 percent urea solution you pour into the tank, here is a bigger question.
At 95K miles, CEL is on and the fault code is P20BD. Something is wrong with the urea heater -- the level sensor was acting up prior to that, a different fault code.
My plan is to replace the heater, likely using OEM part A2124710575. But...how to get to the pump and heater assembly? Both are barely visible under the thick metal cover.
I have heard dealer stories about replacing the whole tank, though it is hard to believe that just the heater assembly cannot be replaced.
Skipping the often asked stuff about DEF, Adblue or whatever kind of 33 percent urea solution you pour into the tank, here is a bigger question.
At 95K miles, CEL is on and the fault code is P20BD. Something is wrong with the urea heater -- the level sensor was acting up prior to that, a different fault code.
My plan is to replace the heater, likely using OEM part A2124710575. But...how to get to the pump and heater assembly? Both are barely visible under the thick metal cover.
I have heard dealer stories about replacing the whole tank, though it is hard to believe that just the heater assembly cannot be replaced.
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Search and you will find:
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https://mbworld.org/forums/m-class-w...ml#post6197505
Thread Starter
Junior Member
Joined: Oct 2016
Posts: 20
Likes: 0
From: California
2011 E350 Bluetec
Follow-up. A few weeks and a few hundred bucks later, I am getting the error code P20E8 (low pressure)
The DEF pump is working (humming, at least),
Both O-rings at the pump have been seated in place at assembly.
DEF tank is quarter full with the lid tight. I was fitting an air balloon instead of it to visually check the pressure, and it did not inflate indeed.
No DEF leaks or disconnected hoses/wires.
Where can the air escape from my DEF tank?
The DEF pump is working (humming, at least),
Both O-rings at the pump have been seated in place at assembly.
DEF tank is quarter full with the lid tight. I was fitting an air balloon instead of it to visually check the pressure, and it did not inflate indeed.
No DEF leaks or disconnected hoses/wires.
Where can the air escape from my DEF tank?
Thread Starter
Junior Member
Joined: Oct 2016
Posts: 20
Likes: 0
From: California
2011 E350 Bluetec
Solved it!
The tank is not pressurized at all, and the pump works two ways -- to deliver DEF to the injector and to purge DEF from the line after the engine is stopped.
Turned out that the pump nipple I had replaced was bent (factory defect), triggering the P20E8 low pressure code.
Replaced the pump assembly with an aftermarket part but swapped in the original Bosch motor to resolve an "open circuit" CEL code.
So far so good.
The tank is not pressurized at all, and the pump works two ways -- to deliver DEF to the injector and to purge DEF from the line after the engine is stopped.
Turned out that the pump nipple I had replaced was bent (factory defect), triggering the P20E8 low pressure code.
Replaced the pump assembly with an aftermarket part but swapped in the original Bosch motor to resolve an "open circuit" CEL code.
So far so good.
