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Old 05-26-2020, 09:07 AM   #1
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2014 Interstate Ext. Coach
Lexington , South Carolina
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Sensors

Anyone having problems with DEF sensors or speed sensors. I bought a 2014 interstate with 14,000 miles 4 months ago. Iíve had DEF problems until finally was told that the (Knox , not sure of that spelling)sensors needed to be replaced. Now multiple warnings with ABS, cruise control, lane assist are caused from speed sensors have gone bad. Is this normal? I have low mileage because the original owners didnít use it much. My technician said problems were more than likely caused from lack of use. Thanks for any advice!
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Old 05-26-2020, 04:03 PM   #2
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I have had one rear wheel speed sensor fail at 40,000 miles (had both replaced) and a front fail at 70,000 miles. I am told that rear sensor failures are common on the 3500 chassis (dual rear wheels). I have seen a lot of NOx sensor issues following low DEF - so I never let my DEF level get low. cruise control, ABS, and ESP all fail (or are turned off) when a wheel speed sensor fails. I tried replacing the front sensor first with a $25 generic sensor then with a $50 name-brand (Bosch) part and the MB software rejected both. So I had to pay $150 for an official MB part (quite possible also made for them by Bosch). I bought a code reader which told me which sensor had failed. I paid to have the rear replaced, but easily replaced the front one myself. (Easily once I finally got the MB one that the software accepted.)
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Old 05-26-2020, 05:50 PM   #3
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I had a sensor fail in the passenger side rear wheel. I had a short in the driver rear wheel sensor wire (they ran a new wire undercarriage).

Seems to be a common problem.
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Old 05-27-2020, 04:36 AM   #4
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Sensors

Thanks guys. I love my Interstate but these sensors all failing at once is debilitating when on the road. Do you think more consistent use will help them last longer?
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Old 05-27-2020, 05:38 AM   #5
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Corrosion from non-use does take its toll and the ones that failed are more susceptible so it stands to reason. Watch your DEF level as has been mentioned and inspect the exhaust pipe frequently for a while for signs of white powder (excessive DEF use) so you know if the DEF injection system was the cause of the NOx sensor failure.
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Old 05-27-2020, 09:51 AM   #6
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The DEF itself does not age well. Sitting in a tank all winter can lead to crystallization as it degrades and that can lead to all kinds of trouble later on.

I use my diesel truck year-round so I avoid that problem.

Is there any way to drain the DEF tank at the end of the season and start each year with fresh fluid?
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Old 05-27-2020, 11:38 AM   #7
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I understood that it degraded more due to heat than cold. I don't think the freeze-thaw cycle leads to crystallization. The tank being under the van and not in the engine compartment, excessive heat should not be an issue. There is a drain on the rear inside corner of the tank- a rubber tube with a stopper. Remove the stopper and tilt it down into a bucket. I drain mine every 2-3 years and use the old stuff as fertilizer in a hose-end sprayer. if you do drain it never start it with the DEF tank empty or your encounter the dreaded restart countdown.
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Old 05-27-2020, 02:29 PM   #8
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Quote:
Originally Posted by n2916s View Post
The DEF itself does not age well. Sitting in a tank all winter can lead to crystallization as it degrades and that can lead to all kinds of trouble later on.

I use my diesel truck year-round so I avoid that problem.

Is there any way to drain the DEF tank at the end of the season and start each year with fresh fluid?
DEF is an aqueous solution of urea and degrades to ammonia at high temperatures not low. About a year at 95-100 degrees, more than 2 years if kept below 75F. If it has a strong ammonia smell, it is getting old. It does freeze and crystallize in the winter at about 15 degrees but it thaws out just fine.
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Old 05-27-2020, 10:37 PM   #9
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Sensors

Thanks for the info.
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Old 05-28-2020, 03:13 PM   #10
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Quote:
Originally Posted by Titus View Post
I understood that it degraded more due to heat than cold. I don't think the freeze-thaw cycle leads to crystallization. The tank being under the van and not in the engine compartment, excessive heat should not be an issue. There is a drain on the rear inside corner of the tank- a rubber tube with a stopper. Remove the stopper and tilt it down into a bucket. I drain mine every 2-3 years and use the old stuff as fertilizer in a hose-end sprayer. if you do drain it never start it with the DEF tank empty or your encounter the dreaded restart countdown.
Where it is ďrear inside cornerĒ?
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Old 05-28-2020, 04:26 PM   #11
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On mine the DEF tank is above the electric step. Rear means toward the rear of the van. Inside means towards the center of the van. It is a rubber hose that comes out of the bottom of the tank and is snapped into a clip at the top of the tank. Unsnap it from the clip and tilt it downward. Remove the cap on the rubber hose. Open the DEF fill cap in the engine compartment to let air into the tank while it drains.
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Old 05-28-2020, 11:45 PM   #12
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Quote:
Originally Posted by Titus View Post
On mine the DEF tank is above the electric step. Rear means toward the rear of the van. Inside means towards the center of the van. It is a rubber hose that comes out of the bottom of the tank and is snapped into a clip at the top of the tank. Unsnap it from the clip and tilt it downward. Remove the cap on the rubber hose. Open the DEF fill cap in the engine compartment to let air into the tank while it drains.
Thanks! Valuable information!
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Old 06-08-2020, 09:16 AM   #13
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Quote:
Originally Posted by The Hallmans View Post
Anyone having problems with DEF sensors or speed sensors. I bought a 2014 interstate with 14,000 miles 4 months ago. Iíve had DEF problems until finally was told that the (Knox , not sure of that spelling)sensors needed to be replaced. Now multiple warnings with ABS, cruise control, lane assist are caused from speed sensors have gone bad. Is this normal? I have low mileage because the original owners didnít use it much. My technician said problems were more than likely caused from lack of use. Thanks for any advice!
I also have a 2014 GT with low mileage and have had problems with both the Knox sensors and the speed sensors. One year ago MB told us the Knox sensors had gone bad and that over idling the engine had irreparably damaged the ďbrainĒ of the
DEF system. It was replaced at a cost of $8000. Beware the white soot in your tail pipe. One month ago I had a speed sensor fail in the rear while leaving the dealership. They replaced it and yesterday I got the same sort of message. I am expecting another failed speed sensor. As I am no longer under warranty, I plan to buy the new sensors,
and have a trusted local shop install them for me. But, I still love my Interstate!!
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Old 06-08-2020, 02:40 PM   #14
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Temperature affects DEF Shelf Life too!

Quote:
Originally Posted by BayouBiker View Post
DEF is an aqueous solution of urea and degrades to ammonia at high temperatures not low. About a year at 95-100 degrees, more than 2 years if kept below 75F. If it has a strong ammonia smell, it is getting old. It does freeze and crystallize in the winter at about 15 degrees but it thaws out just fine.
When purchasing DEF containers, you also need to be able to read the Blue DEF Expiration Date Code. It will deteriorate over time!

Per this chart;
Click image for larger version

Name:	DEF chart.png
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ID:	369767

This video will explain how you can read the code on the container.
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Old 06-08-2020, 07:42 PM   #15
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Long ago I bought it in 2 1/2 gallon jugs and kept the jugs. I refill them at a nearby truck stop which should be fresh given the high thru-put. Price is a bit cheaper there too. Though I got some strange looks when I pulled a Prius up to the Class 8 truck islands.
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Old 06-09-2020, 04:55 AM   #16
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I too use the DEF pumps at truck stops. It’s less expensive and easier than trying to get the 2 1/2 gallon jugs spout into the filler cap without spilling it!
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Old 06-09-2020, 06:08 AM   #17
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I don't use the truck stop DEF pumps directly into the Interstate, I just use them to refill the 2 1/2 gallon jugs. I found that even a slow pour from the jugs would create an air lock. My guess is that the DEF not only goes down the fill tube but also goes down the DEF tank vent line that is just below the fill tube. My solution is to use a funnel with a long neck so that the DEF enters the fill tube below the point of the vent tube joining.
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Old 06-09-2020, 11:11 PM   #18
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Usual use of 2.5 gal jag from Walmart has never gave me problem
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