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Old 07-31-2019, 07:31 PM   #1
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Default DEF replacement

I have a 2017 sprinter Pleasure way Ascent. it's about time to add DEF and I want it full before leaving for our next trip. Is it ok to just add as needed or best to wait until the light turns on to add DEF?
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Old 07-31-2019, 07:45 PM   #2
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Add as needed is when the light turns on. I think it is best to top off before any trip as routine. Generally most trips then you will not need to add DEF while on the road nor need to carry a spare container in you B though you can easily buy it on the road at Walmart, any auto store or truck stop.
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Old 07-31-2019, 07:48 PM   #3
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That is a highly fraught question. I really don't think anybody knows for sure.

I used to be a strong advocate for waiting for the light to come on. That was until I got a CEL light along with a "10 starts remaining" message 5 miles after filling our near-empty DEF tank with cool DEF from the truckers pump along the highway on a very hot Texas day. Of course, it could have been a coincidence, but...

There is a credible theory that there are bugs in the DEF system firmware that can be triggered by a normal "add DEF" condition, and that it is best to keep it topped off in the spirit of letting sleeping dogs lie. Who knows?

There is another theory that letting the tank get empty "exposes the sensors" (or some such) causing them to fail. I do not believe this theory.

I now refill my tank when I estimate it is down about halfway and don't wait for the warning. May or may not be necessary, but there are few arguments that frequent fillings are harmful, as long as you are careful not to contaminate the system in the process.
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Old 07-31-2019, 08:58 PM   #4
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I filled my tank to full regularly before any warning lights, in fact I never had any warnings about low DEF before my DEF saga begin in Texas early this year.

The DEF assembly has 2 level sensors from some kind metal -2 rods, temperature sensor is fully encapsulated in plastic. The heater is the only one which could possibly fail with a very low DEF level, heater is located on the bottom of the DEF assembly.

When we got stuck in Texas, we heard from the service manager that “the tank was dried so the heater fried”. I wouldn’t be shocked if this statement is used as a talking point. In my case I paid for replacing the heater even thou it was the temperature sensor which I learned after measuring the replaced assembly.

Being a little paranoiac after this warranty ordeal I tend to fill my tank as often as it is practical.
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Old 07-31-2019, 09:06 PM   #5
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I wait until the gauge shows slightly less than half. I then open and add a complete 2.5 gallon container of DEF from Wally World. That way I stay away from the potential problem of dry sensors, and I can add the complete container with no overflow or spillage. I find that I'm using about 1 gallon of DEF for every 1,000 miles driven.
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Old 07-31-2019, 09:14 PM   #6
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Quote:
Originally Posted by DUTCH in Atlanta View Post
I wait until the gauge shows slightly less than half. I then open and add a complete 2.5 gallon container of DEF from Wally World. That way I stay away from potentially dry sensors and I can add the complete container with no overflow or spillage. I find that I'm using about 1 gallon of DEF for every 1,000 miles driven.
That is similar to what I try to do. Note however that:
1) Older Sprinters do not all have DEF gauges, so sometimes you just have to use dead reckoning.
2) There are several (at least three) different size DEF tanks in Sprinters, so one's strategy has to be adjusted accordingly.
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Old 07-31-2019, 09:21 PM   #7
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Thanks everyone for your input. I'll be erroring on the side of caution and filling before my light comes on. The dealer service folks told me that I should only need to fill every 8,000 miles and there no gauge to show me a level before the light comes on. That just drives me crazy as I always like to know my fluid levels before a trip.
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Old 07-31-2019, 09:29 PM   #8
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Quote:
Originally Posted by Westie View Post
there no gauge to show me a level before the light comes on. That just drives me crazy as I always like to know my fluid levels before a trip.
I am surprised that a van as new as yours doesn't have a gauge. Are you sure it isn't buried in the menus somewhere?
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Old 07-31-2019, 09:36 PM   #9
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I agree! I may have to dig a little deeper. But the person at the Mercedes service said there wasn't anything on the menu so I stopped looking.
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Old 07-31-2019, 10:14 PM   #10
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I agree! I may have to dig a little deeper. But the person at the Mercedes service said there wasn't anything on the menu so I stopped looking.
I will refrain from editorializing about the likely quality of anything a Mercedes service advisor tells you.

Check your manual.
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Old 07-31-2019, 10:32 PM   #11
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"I will refrain from editorializing about the likely quality of anything a Mercedes service advisor tells you."

That was kind of funny avanti as you kinda just did.

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Old 08-01-2019, 01:27 AM   #12
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My 2015 chassis Sprinter gets about 8,000 miles give or take before the warning light comes on. That was probably what the dealer alluded to. Then it took a full 2.5 gallons and I don't think it fully filled. A one gallon fill would never reset the warning. That's why I recommend topping it off before a trip so you know and can leave a partially empty container at home. Few trips go over 8,000 miles unless you take an extended 2-3 month trip or go a long way like Alaska or if you are a full-timer.
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Old 08-08-2019, 03:56 PM   #13
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Quote:
Originally Posted by avanti View Post
That is a highly fraught question. I really don't think anybody knows for sure.

I used to be a strong advocate for waiting for the light to come on. That was until I got a CEL light along with a "10 starts remaining" message 5 miles after filling our near-empty DEF tank with cool DEF from the truckers pump along the highway on a very hot Texas day. Of course, it could have been a coincidence, but...

There is a credible theory that there are bugs in the DEF system firmware that can be triggered by a normal "add DEF" condition, and that it is best to keep it topped off in the spirit of letting sleeping dogs lie. Who knows?

There is another theory that letting the tank get empty "exposes the sensors" (or some such) causing them to fail. I do not believe this theory.

I now refill my tank when I estimate it is down about halfway and don't wait for the warning. May or may not be necessary, but there are few arguments that frequent fillings are harmful, as long as you are careful not to contaminate the system in the process.
I agree with GeorgeRA
I have a 2014 Agile....low DEF light came on, message regarding limited starts, then at the same time both sensors had a problem. We were on the road with a stop at Las Vegas and it was Saturday. Had to stay in the area for 2 extra days until the Mercedes dealer could replace the sensors and software update. The rear sensor went out again a couple months later.
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Old 08-08-2019, 04:02 PM   #14
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Quote:
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I agree with GeorgeRA
I have a 2014 Agile....low DEF light came on, message regarding limited starts, then at the same time both sensors had a problem. We were on the road with a stop at Las Vegas and it was Saturday. Had to stay in the area for 2 extra days until the Mercedes dealer could replace the sensors and software update. The rear sensor went out again a couple months later.
Which sensors are you referring to, exactly?
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Old 08-08-2019, 04:07 PM   #15
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Dealerships will top off before warning comes. There should be no issue. On my 2015 ascent, I usually top off before long trips. I don’t like to have to be worrying if I will get to a location I can buy some before the warning period is up. No issue to date.
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Old 08-08-2019, 04:13 PM   #16
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I've had my DEF light come on many times but not accompanied by any message of limited starts. There was a message to fill within 500 miles. Are you ignoring the message until you see a count down message?

If I get the light I head to the nearest truck stop, auto store or Walmart on my route. I don't think I've gone over 50 miles after the DEF light came on to refill.

I did get the count down warning once, so experienced the panic, but it turned out not to be DEF or Nox censors but an electrical malfunction and happened after I topped off the DEF. It was screwy since the message was different every time I started the engine. MB fixed it under warranty at about 60,000 miles.
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Old 08-08-2019, 04:25 PM   #17
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A friend of mine is a maintenance manager at a Fedex depot that has a large fleet of sprinter vans. They top off the DEF every night when the vans come in as routine maintenance. However he said a full tank of DEF last about 7000 miles. I top off when the gauge read half empty or so.
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Old 08-08-2019, 05:32 PM   #18
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Default DEF level

Westie,
A Scan guage 11 can be programmed to read out the level of fluid in the DEF tank on a Sprinter van from the OBD port.The codes are recorded in this forum somewhere or I can send them to you.
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Old 08-08-2019, 06:20 PM   #19
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Push pages button until after start and then up arrow 3 times to see DEF level. I have 2018 Sprinter and should work on yours.
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Old 08-08-2019, 09:00 PM   #20
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I will add my 2 cents. My 2014 MB Sprinter does not have a gauge. I routinely fill with DEF whenever the odometer reaches an even thousand miles (i.e. every two thousand miles). This is just an easy way for me to remember. I suppose I could have used every 5000 miles instead, but I wanted to be sure that if I was on a long trip, DEF solution would never be an issue.
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