Def Countdown and Driver's Seat Fuse - FIXED

[dorybixler]

I'm posting this just in case someone else has this same issue. We have a Navion 24' with 37K miles on it and the DEF light with countdown came on during our last trip. We checked the DEF and added 1 Gal of "new" DEF. That was not the issue but countdown remained. We called the Mercedes Dealership in Chandler and asked for Bill Stamper, who is the guy you need to call if you have this issue or any related to sprinter vans or your Mercedes. We prayed it was not the nox sensors that we just replaced 2 years ago. After Victor the mechanic tested all the usual suspected issues, he found that the fuse under the driver's seat was bent! Because the fuse was loose, the nox sensors would not work.
How this happened:
About a week prior we turned our seats around and the long skinny wire underneath that connects to the SRS (seat restraint system) got cut which we reattached but I didn't notice or didn't even think of looking at a fuse. Apparently the fuse box lid got yanked open by the wire and pulled on the fuse. Hard to believe but that was the problem! So be careful turning your drivers seat around. Mercedes should never design the wire this way but that is a whole different rant.
Cudos to BILL STAMPER and VICTOR at the Chandler, AZ dealer. I told him I'd write up this post. When we noticed the issue we were about 100 miles away. He troubleshooted the issue over the phone and then said come in. He knows these Mercedes vehicles well and I would trust ours with him again and again. The dealer number is 480-421-4550

[SocioSam]

Which fuse # - I cannot find a code book for the fuses.

We are getting the DEF check light one and engine light. Happened after we put in DEF. It was Walmart DEF. We had purchased Blue DEF there before but this time they had only their own brand. Immediately after putting some in we got the warning.

[luvlabs]

On the older (pre-2016 chassis) you need to completely fill the DEF tank. No partial fills. Even with the newer chassis, the label says to add at least 2 gallons. Brand of DEF is not important. I use the Walmart stuff all of time and it works fine.