During the first 12,000 miles on my 2014 RV with a MB diesel engine and a Sprinter chasis I have stopped in 5 different MB dealers while traveling with my wife and 2 dogs. The DEF fluid light comes on and tells me I have a certain amount of starts left even when the DEF tank is full! Along with that comes on a check engine light! We had no choice to drive to a MB Sprinter dealer in another state, wait in the lounge with 2 dogs, find a motel for that night or nights! Talk about stress! This has happened 5 times in 5 different states. Several times during the same trip! Anyone have the same problem. I have 2014 Thor Siesta with a MB 188 hp diesel engine. Help!

Bad or stale DEF can cause this. Where did you fill the DEF tank and how old was the fluid?

donn0128 wrote:Bad or stale DEF can cause this. Where did you fill the DEF tank and how old was the fluid? The DEF fluid was from various auto parts stores. It is a mechanical problem not a DEF fluid problem. Pumps have been changed, wires have been changed, computer specs have been changed-you name it!

There unfortunately are way to many problems with the DEF systems. They just don't have them perfected yet. I have had my truck in the shop three times for DEF issues in less than 26k miles. The thing they shouldn't do is threaten to leave you stranded by not letting you start you vehicle, thats BS. I could go with limiting your speed to like 50 MPH but leaving you stranded is ridiculous.

Have you looked for nearby Freightliner service centers? They can service Sprinters too.

I was just reading on one of the Sprinter forums about this same thing and the DEF had crystalized on the feed port in the tanks. They replaced that and it fixed the trouble. Might make the suggestion at the dealer when you take it in. I wonder if letting the rig set without or low DEF in it and the it evaporates and leaves the crystals behind?

Anyone having DEF fluid problems in a MB diesel RV?

14 Replies

RV_kayak_travel
Explorer
Dec 18, 2014
That same problem occured to a friend of mine on his '12 MB 188 hp. It took many part changes, including the two nox sensors, and both computers. He ended up talking to a MB mechanic that told him to "insist" on changing both computers. As I understood what was told to him, there is the main vehicle computer and the emmisions computer. The programs randomly conflict in communication, thus tripping the def warning, and that results in the, so many starts left sequence. They finally caved, replaced the both computers and wella, 20K later, no def issue.
mlts22
Explorer II
Dec 15, 2014
AFIAK, each Mercedes service (either "A" and "B") requires the DEF tank to be flushed in order to prevent crystallization.

If DEF does crystallize/precipitate out, then I wonder about some form of agitation/stirring mechanism in the tank. Could be something passive that helps mix things when the vehicle moves, or active (such as the magnetic stir bar apparatus used in high school chemistry that has few moving parts and just a ceramic coated magnet in the mixture.)
tommykelly
Explorer
Dec 14, 2014
there is a reason Cat. got out of road engine business in the U.S.

and as the winds blow from Red China...here comes the diesel exhaust from all the Hino trucks from the 1960's...billowing smoke..
scmike
Explorer
Dec 13, 2014
I recently bought our first MH (a used Winnebago Via) with the same Mercedes 188hp turbo diesel and had similar problem. Also discovered that the first message I got "Check DEF fluid. See Operator manual" needs to be rest by dealer! Ours would not go out even though manual says it would. We had it at Mercedes/Sprinter dealer and after they replaced first part I made them take on a road test and sure enough it came back. They finally replaced both "NOS" (?) sensors and problem gone for now. Was getting some type of message, either this or the 16 restarts left - every 100-120 miles. Drove 200 miles with no message - small victory!
snoopeme
Explorer
Dec 12, 2014
I have a 2014 Leisure travel van with the same MB Sprinter engine and also got my first low Def fluid warning around 4000 miles or so. I added fluid and no problem. Around 5000 Miles a check engine light came on which was related to the emissions system. A MB DEALER checked it out and reported some kind of sensor needed replacing. It was well under warranty and I'm keeping my fingers crossed! If the government in their infinite wisdom didn't require all that******on the engines we'd get better mileage and have a lot more power! BTW, I add DEF fluid from Walmart, and appreciate the tip to keep the reservoir topped off! Might save some grief later?
1donald
Explorer
Dec 11, 2014
donn0128 wrote:
Bad or stale DEF can cause this. Where did you fill the DEF tank and how old was the fluid?

We have the 2013 LTV Sprinter & we receive the low DEF Fluid warning at approximately 4500 miles. Have added Def. Fluid now three times, but not problems to report. We just pick up two gallon container from Walmart when we receive the warning that the Def Fluid is low & replace.
RckyMtnVia
Explorer
Dec 10, 2014
So far no issues. After traveling 1,500 to 2,000 miles I top up the DEF so that I do not have to worry about the low level warning message.
9er
Explorer
Dec 10, 2014
no issues on mine,guy told me once to keep it full at all times as much as possible
Dakzuki
Explorer II
Dec 09, 2014
No issues on mine.
Butch50
Explorer
Dec 09, 2014
I was just reading on one of the Sprinter forums about this same thing and the DEF had crystalized on the feed port in the tanks. They replaced that and it fixed the trouble. Might make the suggestion at the dealer when you take it in.

I wonder if letting the rig set without or low DEF in it and the it evaporates and leaves the crystals behind?