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MB Paul
MB Paul, Mercedes Technician
Category: Mercedes
Satisfied Customers: 3567
Experience:  Qualified Mercedes Benz Diagnostic Technician - 20+ years experience - Workshop Foreman for Mercedes
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2011 ML350 BlueTec with 70K km shows code P20E8, which I

Customer Question

Hi 2011 ML350 BlueTec with 70K km shows code P20E8, which I reset after learning that it meant low DEF pressure. Research suggests this could be DEF pump, corroded line (not holding pressure) or a sensor. There was no performance change. 200km after the reset, same code. Had a friend with a more sophisticated device look at it, and it showed codes 20e821 and 20e823. We ran an active diagnostic with engine running which showed zero pressure in DEF system. Then forced pump on and it built pressure normally. Forced pump off and pressure fell back. After that, the pressure ran above zero (I don't remember at what level). So it appears that pump was clearly working. But perhaps not consistently. We reset code. About 20 minutes driving later, the code is back. I'm handy, but not interested in doing heavy duty repairs myself. Just don't want to pay big $$ for a pump if that's not the problem, and don't want to bs'd at the repair. Insights appreciated. Mike
JA: Have you seen this code before? Have you tried a hard reset?
Customer: As noted above, 2-3 times in 2-3 weeks. Not sure what a "hard" reset is, but I've reset the code first through a smartphone app (twice) and most recently this morning through a very sophisticated OBD II reader.
JA: What is the model of your '11 Mercedes?
Customer: Pearl...are you reading this stuff?? :) AS PER MY ORIGINAL NOTE...ML350
JA: No. I'm the Mercedes Mechanic's Assistant. Are you fixing your ML350 yourself? What have you tried so far?
Customer: OK, read the original note, which so far has all the answers you're asking for. I'll wait...
JA: Anything else you want the mechanic to know before I connect you?
Customer: nope
Submitted: 10 days ago.
Category: Mercedes
Expert:  Lou P. master tech replied 10 days ago.

Hello, my name is***** and i will do my best to assist you.I am going over your story now and will reply back soon with some info,thanks!

Expert:  Lou P. master tech replied 10 days ago.

the 20E821 and 20E823 do not look like normal codes for mercedes, i will see if they show anything, may i have your vin?

Customer: replied 9 days ago.
Hi Lou - thx for your help. VIN # is 4JGBB2FB4BA644858. I'm travelling for work over the next few days so please excuse me if I can't reply immediately to any questions you have.
Customer: replied 1 day ago.