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2011 adblue heater and processor failure

M-Class (W164) 2006-2011: ML280CDI, ML320CDI, ML420CDI, ML350, ML500, ML550

2011 adblue heater and processor failure

Old 03-01-2019, 05:48 PM
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2011 Mercedes E350 BlueTEC
P20E8 Still an Issue

Originally Posted by keithwbloom View Post
OK, not pictured here is the removal of the four nuts that fasten the plastic tank cover and the four nuts that secure the two metal band tank support straps.

Photos start here because I wanted to take lots of pictures to make sure I remembered where to reconnect everything and where the zip ties were to be restored when finished. This is the pump unit on the lid of the additive tank. It has to be disconnected and removed to access failed pre-heater parts which are located inside the additive tank.

Pretty simple. I did it on the curb in front of my home (I do not have a garage or driveway) and it took me about 90 minutes, start to finish, feeling my way through the process. My heater codes have not since returned, but now I have a P20E8 control module related code that will not clear. So unfortunately, it is at the MB dealer getting that sorted because I just cannot put off re-registration any longer and I have to get emission inspection to do so. I am already 10 days overdue. :-(
I know it's been a while since you did this work but I was hoping you could share the model of the Mercedes you did the work on. Your profile next to the post lists a couple of Audis but no Mercedes. I just purchased a used 2011 E350 BlueTEC from a Honda dealer's used lot. Shortly afterward I the MIL came on and I read out the P20B8 code Reductant metering unit heater control circuit high. The Honda dealer made good on it (or at least he said he did) and replaced the heater (again, at least he says he replaced the heater). Unfortunately a couple of months later, the MIL came on again with the same code. Of note, shortly after I got the car back from the shop I got the MIL with a P20E8 code, reductant press low. I shut off the car, opened the reductant tank cap, put it back on tight and started the car again...cleared the code and didn't get another indication. I assumed there was some air in the system from when they changed out the heater. But, as I mentioned, about two months later I did get the P20B8 code again.

I've read that these codes take a bit of time to manifest and I'm wondering if the dealer cleared the code and called it good without replacing the heater. I don't drive this car every day...only on weekends for the most part because I have a company car. So if the codes do take time to manifest that time frame is not out of the realm of possibility. I figure my best course of action is to gather as much info on how to change the heater and be prepared to do it next time I get the MIL (I cleared the code again and have not gotten it another for a week or so). It looks to me as if you attacked from the bottom of the vehicle and not through the trunk...which is what I thought I would have to do. I guess there aren't many Mercedes owners who work on their own vehicles...your DIY is one of the best and one of the few I have found. So, thank you for the pics and the info!! Anything additional you can offer would be greatly appreciated! I'm fairly adept at repairs but by no means a pro. I have a good selection of tools, including air tools but I'm already noticing that Mercedes uses some pretty esoteric hardware...star pattern nut fasteners for instance...guess I'm going to have to buy special sockets to undo those...never seen them before. Again, thanks for your post, hope to hear from you soon.

Last edited by stiknrudder; 03-14-2019 at 12:18 AM.
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Old 03-06-2019, 11:25 AM
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2003 E320
I had this problem on my ML. First my local mechanic didn't know what was causing my car to go into limp mode.
Took it to MB dealer and they quoted $2200 for a new DEF heater.

Before giving them the green light, I research and came across this thread.

Also came across this article and instructions on how to change DEF heater, so I decided to do it myself.

Got it done in under 2 hours.

Thanks all.
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Old 05-17-2019, 01:39 PM
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1980 450SL, 1993 300CE,2006 E350,2011 ML350 Bluetec, 2000 E430
Service Campaign for 2009-2011 ML's heater errors

After a DEF pump change for a different reason (broke the nipple off and bought a new pump after several failed gluing attempts before discovering Xemodex had a wonderful Nipple Repair Kit), and within days had the dread heater peformance error codes, mine was P20B6 which my Autel scanner decodes as "Reductant Metering Unit Heater Control Circuit Peformance, so initially like a sucker I replaced the supposedly bad heater with a new Xemodex replacement, but... no luck.. .still codes despite perfect 2.2 ohm resistance on the old heater and the new. Then I started picking up these threads of people replacing their tanks again and again believing the *heaters* were faulty, but only just occasionally making mention of "Software Update" for the SCR unit, which seems to help.

Well, as it turns out, Mercedes had a Service Campaign for the SCR update in 2011...

Campaign - SCR And Engine Control Module Software Update
Campaign No. 2010110005, May 2011

...and supposedly these do not expire, so if your vehicle is throwing heater related codes andis a 2009 to 2011 that might be one of the 12,519 believed affected, According to the notes I have, I believe you campaigns are like recalls and to not expire, so your might be entitled to a no cost try on this item. In the description, it talks about updating the SCR and Engine Control Unit.software. so you might be able to get that important update by just mentioninam

As an aside, I think one reason it is so hard for people to connect the dots on these failures is the huge range of terminology used. The same compoment might be called an AdBlue tank, or a DEF (Diesel Exhaust Fluid, or is it Diesel Emmisstions Fluid) tank, or a Urea tank? Is the whole system the AdBlue system, or is it the DEF system or (as the smog regulations call it), the SCR or Selective Catalytic Reduction system? Searches really need to include all the terms to get the complete result.
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