2020 BABY Duramax (check engine lite)

[wildbill1973z28]

Oh GREAT ODT WORLD!WHO KNOWS ALL- seen all-experience all. Even seen the wind .
OK here’s the story 16,000 miles check engine light comes on. Prior to this this 3.0 L diesel had been getting 28 mpg! Now after visit to dr. The baby Duramax will not get 24 mpg. Went back to dr. Chevy cannot find anything?(Oh great minds of the Odt world remember this all of this was done over the computer calculations I did not keep up with gallons are marks are totally relied on the computer)
1.Light come on One star called Said if check engine light went to flashing it would shut down regardless of where I was.
2.computer was reset at every tank(always at least 27mpg)
3 tank mpg was always on the 400 miles setting.
4. On 3 tank since dr. Visit I have reset the factory settings!
5.so what do I do now?

 

[user 71]

Don’t trust the onboard calculator. Do the math yourself.

My truck’s onboard computer regularly says I’m getting an average of 17 mpg - resetting every fillup. However the math - odometer divided by gallons required to fill it up would suggest I’m getting 15.8.

I think the computer uses a moving average or something like that. Regardless it seems deceptive.

What did the window sticker say you would get when you bought it?

My hand calculations for my truck are in range of what the sticker stated I would get.

 

[wildbill1973z28]

Don’t trust the onboard calculator. Do the math yourself.

My truck’s onboard computer regularly says I’m getting an average of 17 mpg - resetting every fillup. However the math - odometer divided by gallons required to fill it up would suggest I’m getting 15.8.

I think the computer uses a moving average or something like that. Regardless it seems deceptive.

What did the window sticker say you would get when you bought it?

My hand calculations for my truck are in range of what the sticker stated I would get.

sticker said 27-33

 

[Bass Akwards]

Did you change tire size? I had a 16 1500, thought I was getting mid 20's mpg.
While driving with gps and the "your speed is" radar signs on the side of the road,the speedometer were never the same.
I was working for a customer one day who worked for a tire store asked me how was the mpg,"great I said" compared to other 1500's, He then asked about the differences between the gps and speedo, he already knew the answer.
Chevy and others I assume, install smaller diameter tires from the factory to make it appear like it had a higher mpg to meet epa standards, needing tires I had him install the correct size tires based on factory gear ratios, the ride home the speedo an gps were a match, but the mnp's went to 17ish.

 

[Dogtown Darren]

I'd suggest searching for a GM specific forum for your truck and/or engine. There's a wealth of information out there in various forums/Facebook groups. Often times, there will be folks that have experienced your same issue that can offer solutions/things to avoid.

I have a Toyota truck, and I've found that such forums/groups have provided me with a ton of information.

Good luck!

 

[Cadcom]

Are you buying fuel from the same location each time? Maybe try a different station. Don’t know much about diesel but maybe changing up the fuel might help.

 

[THREEJAYS]

Sounds like you done wore it out. Better get a new one quick

 

[dcline9163]

I have not experienced that on mine yet, but I do know some areas add an additive to fuel because of where the fuel comes from. I try to buy my fuel from a place that goes thru a lot of diesel. If that additive is added it raises the price of the fuel too. For instance Rockmart it's around $2.45 a gallon but Cedartown towards Alabama and Rome it runs about 1.90 to 2.10 per gallon.

 

[jdav]

Don’t trust the onboard calculator. Do the math yourself.

My truck’s onboard computer regularly says I’m getting an average of 17 mpg - resetting every fillup. However the math - odometer divided by gallons required to fill it up would suggest I’m getting 15.8.

I think the computer uses a moving average or something like that. Regardless it seems deceptive.

What did the window sticker say you would get when you bought it?

My hand calculations for my truck are in range of what the sticker stated I would get.

Don’t trust the onboard calculator. Do the math yourself.

My truck’s onboard computer regularly says I’m getting an average of 17 mpg - resetting every fillup. However the math - odometer divided by gallons required to fill it up would suggest I’m getting 15.8.

I think the computer uses a moving average or something like that. Regardless it seems deceptive.

What did the window sticker say you would get when you bought it?

My hand calculations for my truck are in range of what the sticker stated I would get.

Totally agree. My LML Duramax onboard mileage calculator is off but my new L5P Duramax onboard mileage calculator is 4.5-5 mpg off every time I fill up & only 1 month old.

 

[wildbill1973z28]

Did you change tire size? I had a 16 1500, thought I was getting mid 20's mpg.
While driving with gps and the "your speed is" radar signs on the side of the road,the speedometer were never the same.
I was working for a customer one day who worked for a tire store asked me how was the mpg,"great I said" compared to other 1500's, He then asked about the differences between the gps and speedo, he already knew the answer.
Chevy and others I assume, install smaller diameter tires from the factory to make it appear like it had a higher mpg to meet epa standards, needing tires I had him install the correct size tires based on factory gear ratios, the ride home the speedo an gps were a match, but the mnp's went to 17ish.

No still stock every thing! Just the rest of the ck engine lite