DEF Problem

[Storm19e]

Just purchased a 2013 Thor Citation, on the way home the DEF light came on,

no problem filled it when I got home with two gallons of Peak Blue, and the light went off after three cold starts. Within a few days the light came back on.
Took it to Mercedes and was told the DEF was contaminated and would cost

$9000 to repair! Bought it from a party who had most all the maintenance done by Mercedes, doesn't make any sense the DEF would be contaminated.
He had the Peak Blue he was using tested it was not out of date and checked ok.


Storm19e

[TurnerFam]

get a second opinion, or even easier, call Mercedes for a tech to guide you through what the light may actually mean - it could be a simply n0x sensor out of 'timing', etc. No worries.

[Storm19e]

Thanks for the reply, the first call I got for the dealer was it was only a sensor, got a second call the DEF was contaminated cloudy ad has a bad smell, said like paint thinner, and entire system had to be changed. Hard to believe that the seller would have put a contaminate in it accidently he is a car guy, and had most of the maintenance done at a dealer (All documented).

They immediately assumed that someone put the wrong fluid in, but then said they did not know what the contamination was. The coach is still is still under warranty but not covered because of the assumption.

I called the sellers Mercedes mechanic and he said flush it, change the NOX sensor. and it should be good to go.

[TurnerFam]

depending on the location of the DEF, it's probably not an uncommon accident to put diesel there instead.

In all our years and 85,000 miles and DEF fills with our coach, I've never had any issue with the DEF liquid itself, though some have warned that reports have been made that some will purchase DEF containers, use the fluid, then refill with water and return for a refund, as unused. The seal, though, if intact, should let you know that the new container you purchase has not been 'reused', if you know what I mean.
I always use the W*mt blue 2 1/2 gallon jug, with flex spout, and add an additional flex spout to refill my DEF tank by hand. I've maybe used an actual truck-stop DEF pump maybe once, until I realized that after filling my diesel, which has a fill on both sides near the front, I had to crank and move the coach 25' in order for the DEF pump hose to 'reach' my DEF tank, I decided not to go thru that process anymore - plus, if I remember correctly, I had to go back inside the truck stop and stand inline to either get a refund of overpayment if I couldn't pump as much as I already paid or was authorized for, or I had to go back in and do another reauthorization of the DEF pump, whatever....too much trouble.

[Storm19e]

Thanks for the reply the coach only has 30,000 miles. The dealer told me it wasn't a water contamination, and wasn't sure what it was. The seller used Peak Blue in the 2.5 gallon box and so did I when I refilled it after getting it home. The DEF was topped off by the seller before we took delivery, had his DEF checked was not out of date or bad. We got 200 miles before the light went off.


I just hope the dealer isn't being dishonest, probably need a second opinion and a sample of the DEF in the coach. The filler is under the hood next to the radiator tank, some have accidently put DEF the radiator tan k but not into the DEF the cap is clearly labeled DEF.

Thanks,
storm19e