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Discussion Starter · #1 ·
I know there are a lot of posts about DEF, but this is a topic that I have not seen addressed.

2018 Colorado Diesel
224 miles
Stock (But not for long)

I was looking around the computer system with an OBD II reader and found that the system was reporting the DEF level at 45 percent. This, of course, should not be after only 224 miles. Thinking that the dealer did not fill the DEF tank before delivery, I took the truck into the dealer. The dealer tried to add DEF, and the tank immediately overflowed. Thus, we verified that the tank was physically full at, or above 100 percent. The dealer then connected his OBD II reader and got the same result; 45 percent full. He tried to refresh the data, and reset the sensor feed, but still the same reading. The dealer could not find any technical bulletins, or software upgrades. He is contacting GM for directions.

I will, of course, post an update when a solution is found, but I was wondering if anyone else had this sort of sensor problem. I have seen reports of "Low DEF" warnings that did not seem to make sense. Some of these may have been sensor issues like mine. In any case, it might be worth checking if you have an OBD II reader available.
 

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I have the very same issue, my OBD reader shows between 45-48%, even after I filled the tank to maximum. I'm very interested that I'm not the only one with this issue. It's very irritating, because 90% of the reason I bought a scan tool was to monitor the DEF level


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I have the very same issue, my OBD reader shows between 45-48%, even after I filled the tank to maximum. I'm very interested that I'm not the only one with this issue. It's very irritating, because 90% of the reason I bought a scan tool was to monitor the DEF level


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Any updates OP?


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Using OBD Fusion on my phone, with a Bluetooth connector to the OBD port, the DEF level reads fine along with everything else. It definitely can work. It would be interesting if someone near you has this setup to see what it does. Maybe swing by an auto parts store and try a different scan tool?

For shitz and giggles, I plugged my Foxwell scan tool into my truck, it is a $20 cheapie and does not offer the menus needed do much more than clear codes.
 

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Discussion Starter · #6 ·
Using OBD Fusion on my phone, with a Bluetooth connector to the OBD port, the DEF level reads fine along with everything else. It definitely can work. It would be interesting if someone near you has this setup to see what it does. Maybe swing by an auto parts store and try a different scan tool?

For shitz and giggles, I plugged my Foxwell scan tool into my truck, it is a $20 cheapie and does not offer the menus needed do much more than clear codes.
Thanks for the info, Duken4ever. I am using OBD Fusion, and the level reads incorrectly. Since you get the correct level with the same program, I think that it is a malfunction in my particular vehicle. I will be interested to see what GM has to say when they finally get back to me.
 

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Thanks for the info, Duken4ever. I am using OBD Fusion, and the level reads incorrectly. Since you get the correct level with the same program, I think that it is a malfunction in my particular vehicle. I will be interested to see what GM has to say when they finally get back to me.
I do remember that I had to manually enter the calculation for the DEF level and it did not work at first, probably because I messed it up!

A total data dump of all the values I am using for the DEF level in OBD Fusion are:

Information:

Name = DEF Level
Description = DEF Level
Category = Engine
Manufacturer = Generic

Units:

Min Value = 0
Max Value = 255
Metric to English Scale Factor = 1
Metric to English Offset = 0

OBD Information

Module/Header = ECM
OBD Mode = 01
PID Number = 85
Priority = Low

Equation = (100/255) * F

I figure it is worth going line by line to make sure for ya. On the equation, there are blank spaces between the 2nd parentheses, * and F.

I ran it today, it is working perfectly - my DEF was at 44 last time I looked awhile ago, it is down to 38 now. Hoping GDE releases their tune before I have to add more DEF :laugh:
 

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That's 52 pages of reading on mobile, thank you though


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Thought people were asking for help understanding??? Sorry i cant learn it for you too :kiss:
 

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My dealer is actually working with GM engineers on this issue. They replaced the sensor and have continued seen errors popping up so it looks like this may be a widespread issue. My truck has been with them for a few days and they still haven’t fixed the issue so will keep you guys posted.


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The dealer just got back to me. Apparently there is an ECU update which was required for my 2016. I don’t know whether this applies to others but after swapping out to new sensor this fixed my issue.


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I guess I'm late to the party. That seems to be my M.O.

I'm having the same issue with my 2019 LT Duramax. The DEF gauge in OBD Fusion reads around 40% no matter the actual tank level. It also seems to spaz out when there is a lot of vehicle motion.

I don't seem to have access to the same parameters as provided by Duken4evr. I get the impression that the parameters presented by the vehicle and the options available in OBD Fusion have changed since this discussion was started. My DEF gauge monitors a parameter called "DEF Tank Level".

Is there any more recent information available on this issue?
 

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I guess I'm late to the party. That seems to be my M.O.

I'm having the same issue with my 2019 LT Duramax. The DEF gauge in OBD Fusion reads around 40% no matter the actual tank level. It also seems to spaz out when there is a lot of vehicle motion.

I don't seem to have access to the same parameters as provided by Duken4evr. I get the impression that the parameters presented by the vehicle and the options available in OBD Fusion have changed since this discussion was started. My DEF gauge monitors a parameter called "DEF Tank Level".

Is there any more recent information available on this issue?
Out of curiosity. Is the DEF level readout in the DIC the same as on your OBD Fusion?
 
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Out of curiosity. Is the DEF level readout in the DIC the same as on your OBD Fusion?
Left out that part. Sorry. No the DEF level in the DIC appears to be correct.
 

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If the DIC reads full when the tank is full, it does not seem to be a problem. Something to do with your scanner. Would not worry about it.
 

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When I tried to post this reply, yesterday, the site went down for maintenance.

Solved the problem. What I missed was that Duken4evr set up a user defined PID. I did that, using his values, and I got the same basic reading as I had been, but the reading was a bit more stable. I guess it's much closer to 30% than 40%. Anyway, what I had to do was add a 3.14 multiplier to the equation. Now the OBD Fusion number matches the DIC at one data point. I'll watch it as fluid is consumed to see if the OBD Fusion gauge tracks the DIC value.

Thanks for the replies.
 
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