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DEF Sending Unit and derating of power?

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CJZKU93

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So last Wed, 6/29/22, my 2021 Ram 3500 DRW diesel truck with 16,000 miles throws a check engine light and my DEF gauge does its cycle and then goes to empty. I know there is half a tank of government juice but I add another 2.5 gallons and the gauge still shows empty. I call the local dealership and they are like its probably a sensor issue bring it in next Tuesday and we will check it. I ask if it is OK to drive and the service guy is like if you go 600 miles it will derate the power and you will be in limp mode. So I take the truck in today and it is the sending unit on the DEF pump and they will have to order it. It will be 10 days but they will ask for special handling so hopefully in a week they will get the part. I ask about the computer derating the power on the truck and the guy I am working with today is like well you really need to just to not use it cause it could derate the power really at any time, not just after so many miles and you will be stuck limping a long at 5 miles an hour.
I have gotten two different answers from this service department as to what will happen driving with the check engine light on for a problem with the sender on the pump for the DEF. Currently I am on a trip to my mom's place in west central Kansas and its not hard to be a good distance away from things with out trying to hard. I really need to use my truck because getting everyone into mom's small car is not exactly a workable option if we want to go do something. I am hoping the collective knowledge here can tell me somethings the service department at the dealership is providing confusing answers on. Has anyone had this kind of issue and did the computer just throw you into limp mode when ever it decided or were you still able to use the truck?
I am becoming very suspect of Dodge dealer service departments because I have had to go in on two different occasion to two different service departments and gotten less then stellar results.
 
It will give you a millage count down before the derate, i have gotten the derate far to many times!
 
H3LZSN1P3R said:
It will give you a millage count down before the derate, i have gotten the derate far to many times!
Click to expand...

Ok so I will add a layer of complexity to the question. Reading the owners manual (which will loose me my manly man card I'm sure) says that if there is any issues with the DEF system you will get a chime and warning messages on the display that you need to add DEF and eventually will get the mileage count down. The Dealer says the issue is with the sending unit on the DEF pump that is the issue. So that would be part of the DEF System. My truck is not doing any of the things the manual says it will do if there is a problem with the DEF system. My DEF gauge reads empty but I am not getting any notices to add DEF or the count down on mileage. I just have the gauge that reads empty and the MIL indicator on. Which seems to go against what the owners manual says should be happening.
 
CJZKU93 said:
Ok so I will add a layer of complexity to the question. Reading the owners manual (which will loose me my manly man card I'm sure) says that if there is any issues with the DEF system you will get a chime and warning messages on the display that you need to add DEF and eventually will get the mileage count down. The Dealer says the issue is with the sending unit on the DEF pump that is the issue. So that would be part of the DEF System. My truck is not doing any of the things the manual says it will do if there is a problem with the DEF system. My DEF gauge reads empty but I am not getting any notices to add DEF or the count down on mileage. I just have the gauge that reads empty and the MIL indicator on. Which seems to go against what the owners manual says should be happening.
Click to expand...
How long have you drove like that?
 
Did you or the dealer read the code that was thrown?
I am on extended trip and at ~12,600 miles I got a Ding and CEL illuminated. Read the code and both P203f & P218f were read. Both DEF issues. I reset codes and ran 120 miles no issues. Next morning we headed out and got CEL, set about 6 miles into trip. Read code now it's just P218f. Reset and no issues on next 200 miles. Next leg it set .5 miles after start. Reset and ran near 300 miles and no issue. We are stationary for 6 weeks,so been driving without towing and not a peep from ECU. ??

Sent from my SM-P610 using Tapatalk
 
Brewmark said:
Did you or the dealer read the code that was thrown?
I am on extended trip and at ~12,600 miles I got a Ding and CEL illuminated. Read the code and both P203f & P218f were read. Both DEF issues. I reset codes and ran 120 miles no issues. Next morning we headed out and got CEL, set about 6 miles into trip. Read code now it's just P218f. Reset and no issues on next 200 miles. Next leg it set .5 miles after start. Reset and ran near 300 miles and no issue. We are stationary for 6 weeks,so been driving without towing and not a peep from ECU. ??

Sent from my SM-P610 using Tapatalk
Click to expand...
Dealer read the codes.
 
H3LZSN1P3R said:
Interesting it should have thrown the derate countdown by now
Click to expand...
That is what confuses and worries me.
I have pointed out to a couple of different service departments that there oddities about the instrumentation on the truck.
Example: the TPMS system is almost and instant read system. I have aired up the tires on the truck and anyone in the truck sitting in the truck can call out pressure changes in real time. Its not delayed like most TPMS are. How ever the system has never had the system throw a warning that the tires on the truck are low. I had the dealer do a 7 tire tire rotation on the truck (getting that was a fight) and when I got the truck back the 4 tires across the rear ranged from 75 down to 40 pounds. I never got a warning that the tires with 40 pounds in them were low.
Another thing I find odd. The truck came with a 50 Gallon tank. I made it a practice to fill the tank when it got to half a tank. At half a tank I will consistently be putting in between 27 or 28 gallons. As the price of diesel started it's rocket ride up I would fill it when it would get to a quarter of a tank to avoid the daily price hikes. I am consistently putting in 14 or 15 gallons when it should be more in the neighborhood of 12.5. Most of the answers I get go down the change of volume with temperature. I do understand volume change with temperature I just have a problem with the consistency of what I am putting in verses what a half or quarter of a tank should mathematically be.

I am tending to think that the computer system in the truck has some kind of issue but I am told there is no way to check or calibrate the system.
 
CJZKU93 said:
Example: the TPMS system is almost and instant read system. I have aired up the tires on the truck and anyone in the truck sitting in the truck can call out pressure changes in real time. Its not delayed like most TPMS are. How ever the system has never had the system throw a warning that the tires on the truck are low. I had the dealer do a 7 tire tire rotation on the truck (getting that was a fight) and when I got the truck back the 4 tires across the rear ranged from 75 down to 40 pounds. I never got a warning that the tires with 40 pounds in them were low.
Click to expand...
3500’s don’t have TPMS, they have TPIS (information system instead of monitoring system). You will not be alerted for low tire pressures. You have to manually pull up the screen to view the tire pressures.
 
CJZKU93 said:
That is what confuses and worries me.
I have pointed out to a couple of different service departments that there oddities about the instrumentation on the truck.
Example: the TPMS system is almost and instant read system. I have aired up the tires on the truck and anyone in the truck sitting in the truck can call out pressure changes in real time. Its not delayed like most TPMS are. How ever the system has never had the system throw a warning that the tires on the truck are low. I had the dealer do a 7 tire tire rotation on the truck (getting that was a fight) and when I got the truck back the 4 tires across the rear ranged from 75 down to 40 pounds. I never got a warning that the tires with 40 pounds in them were low.
Another thing I find odd. The truck came with a 50 Gallon tank. I made it a practice to fill the tank when it got to half a tank. At half a tank I will consistently be putting in between 27 or 28 gallons. As the price of diesel started it's rocket ride up I would fill it when it would get to a quarter of a tank to avoid the daily price hikes. I am consistently putting in 14 or 15 gallons when it should be more in the neighborhood of 12.5. Most of the answers I get go down the change of volume with temperature. I do understand volume change with temperature I just have a problem with the consistency of what I am putting in verses what a half or quarter of a tank should mathematically be.

I am tending to think that the computer system in the truck has some kind of issue but I am told there is no way to check or calibrate the system.
Click to expand...

That's likely due to the tire-fill assist, even if you didn't call it up.

The 50 gal tank reserve is like 5 gallons that factors in there somewhere. I think the setting in the BCM is 8% to indicate Empty.

As Jimmy said, 3500 have TPIS, not TPMS. It can be changed to TPMS with AlfaOBD. So, it's working as designed. I guess it's not surprising the SA or techs at most dealerships don't know this.

P.S. I wish my tire fill assist worked as well, I'm lucky it does what it's supposed to half the time.
 
CJZKU93 said:
That is what confuses and worries me.
I have pointed out to a couple of different service departments that there oddities about the instrumentation on the truck.
Example: the TPMS system is almost and instant read system. I have aired up the tires on the truck and anyone in the truck sitting in the truck can call out pressure changes in real time. Its not delayed like most TPMS are. How ever the system has never had the system throw a warning that the tires on the truck are low. I had the dealer do a 7 tire tire rotation on the truck (getting that was a fight) and when I got the truck back the 4 tires across the rear ranged from 75 down to 40 pounds. I never got a warning that the tires with 40 pounds in them were low.
Another thing I find odd. The truck came with a 50 Gallon tank. I made it a practice to fill the tank when it got to half a tank. At half a tank I will consistently be putting in between 27 or 28 gallons. As the price of diesel started it's rocket ride up I would fill it when it would get to a quarter of a tank to avoid the daily price hikes. I am consistently putting in 14 or 15 gallons when it should be more in the neighborhood of 12.5. Most of the answers I get go down the change of volume with temperature. I do understand volume change with temperature I just have a problem with the consistency of what I am putting in verses what a half or quarter of a tank should mathematically be.

I am tending to think that the computer system in the truck has some kind of issue but I am told there is no way to check or calibrate the system.
Click to expand...
Vehicle fuel gauges have always worked in that manor. Everything you state is working as designed the DEF issue not throwing a derate countdown could be due to the latest update for the def system on these trucks
 
The dealer service department got the parts in finally and replaced the pump and sending unit on my truck this morning. During the two weeks of having the issue the DEF gauge always read empty and the MIL light was on. I didnt get any notices from the system, the warnings that the owners manual said should occur did not happen. I did not get any notices about issues with low DEF or the dreaded mileage count down to derated power and only going 5mph. The issue with the gauge and the MIL indicator started on July 5th so I have had the issue going on for 9 days now and have driven about 700 miles in that time. I watched the DEF Filter and it seemed to be acting the way it normally does. I have only seen it get to the first line and then it cleans out the partials and starts over.
 
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