Good morning. I have a 2011 ML 350 BlueTec diesel. I have a CEL with a error code of 20B91B: Output for heating element for pressure line "AdBlue" has an electrical fault or open circuit. The part needed is 164.470.01.24. How hard is this to change DIY? Has anyone gone down this path before? Thanks. Paul

 

I think you had the same problem as me. See this thread. P20B9 is the heated pressure line. I installed it myself. It's one heck of a job but worth it to save money. I hope you have or have access to a lift. Doing it on a driveway will be absolutely horrible.

https://mbworld.org/forums/m-class-w...zle-broke.html

 

Hi, thanks for this reply from back in June. Would you know what fuse or breaker controls this heated pressure line? I have “tuned” out the AdBlue system, but I have a CEL because the heater line is INOP. I did look at the level of work, and would just like to eliminate the CEL. My system does not use DEF anymore. Thanks for any help.

 

I've had this code for sometime P20B9 on my code reader and P0B91B on my Star C6 machine. Whilst I can see that replacing the Adblue Pressure Line Heater will be nasty job, but I will gladly do it if it will definitely cure the CEL coming on.
I ask this as there are several factors that make me think it might be some sensor giving incorrect information down the line to give the impression the pressure line heater, (or the wiring to it) is faulty when it is not.
If I check without the CEL on with the code reader, it shows just one Error Code, P20B9. If I check it with the code reader, with the CEL on, it shows 2 Error Codes but only lists one P20B9.
There are never any Error messages shown on the dashboard even when the CEL is alight.
When I leave my house from cold the CEL light comes on every time after 4 +/- miles. If I then stop erase the codes, it then carries on perfectly, be it for 20 or 300 miles. Why?? Either there is an electrical fault or there is not. (If you erase a code that tells you that you have a faulty wheel speed sensor, the ABS light comes on again the moment the road wheels start turning). Electricity travels at the speed of light, either it is making the connection or it is not.
As The official MB wiring diagram shows the Pressure Line Heater element as being in the AdBlue Tank Module, (I'll gladly post a copy if anyone is interested), I changed the Tank Module with a brand new genuine Bosch unit, but obviously to no avail,.
With the CEL coming on regularly after 4+/- miles the only thing that can have changed in that time is the temperature of something. But what? The new Tank Module contained a new Tank Heater and a new AdBlue temperature sensor. I've checked the Exhaust Temperature sensor upstream of the Cat and that checks out perfectly with Star 'Actual Values'.
It says in the manual that AdBlue freezes at -11°C and only then will the heaters start working. I now live in Southern Texas where the temperature is around +90° F every time this happens. Why does the car even test a component that is not needed for use at this present time?
All this aggravation over something I'm never going to benefit from. In the 'big freeze' in February the temperature never got down to -11°C (and that was the longest cold spell for Houston for 125 years).
Anybody experienced the same and can advise what might be causing the problem if not the AdBlue Heater line itself?