2018 premiere diesel declining mpg

[tunkertrigger]

I posted before on 5/12/25 about the purchase of my 2018 'Nox Premiere diesel. It has driven well since then but about 10 days ago the problems began. First, engine light came on and
I determined with my Tom Swift Code breaker that I had a P2457 warning. This has to do with EGR system. Since then my mpg has begun to decline. At purchase, I got 40-41 mpg. Now,
it's down to no better than 36 mpg. It is almost due for a 5k service so am hoping for improvement. If not, that's not good enough for a diesel with fuel prices the way they are in my area.
It will be sayanora sucker! Really thinking about a Honda Ridgeline. Drove one and was impressed. Oh BTW, dealer was no help. Not impressed and I have owned many Chevies. This one is not even American made!

 

[dieselloverfr06]

I posted before on 5/12/25 about the purchase of my 2018 'Nox Premiere diesel. It has driven well since then but about 10 days ago the problems began. First, engine light came on and
I determined with my Tom Swift Code breaker that I had a P2457 warning. This has to do with EGR system. Since then my mpg has begun to decline. At purchase, I got 40-41 mpg. Now,
it's down to no better than 36 mpg. It is almost due for a 5k service so am hoping for improvement. If not, that's not good enough for a diesel with fuel prices the way they are in my area.
It will be sayanora sucker! Really thinking about a Honda Ridgeline. Drove one and was impressed. Oh BTW, dealer was no help. Not impressed and I have owned many Chevies. This one is not even American made!

I know about this problem. I caused it to occur with the way I was driving it early on in the ownership of my 18; Premiere Diesel. It was covered under the Emissions warranty which lasts for 8-10 years and I think80,000 or 100,000 miles. You should be covered unless you have driven it more miles.

 

[tunkertrigger]

I know about this problem. I caused it to occur with the way I was driving it early on in the ownership of my 18; Premiere Diesel. It was covered under the Emissions warranty which lasts for 8-10 years and I think80,000 or 100,000 miles. You should be covered unless you have driven it more miles.

Thanks for the info. Appreciate that. I guess we'll see. It's at the dealer right now but they haven't mentioned that warranty yet. They discovered that the Particulate Matter Sensor is bad. So, it is being replaced because it's causing the EGR valve to be inoperable. I do appreciate the feedback.

 

[tunkertrigger]

Well, here's an update on my '18 Premiere diesel. Picked it up at the dealer after spending almost a grand on a new "particulate sensor" replacement. On the way home, the same engine trouble light came on as they told me it might but then the low "exhaust fluid" warning came on. Now its only been a few thousand miles since since I added some to it. Of course, it goes into this stupid warning system that I only have a few miles to get it refilled. Who are the idiots that engineer this kind of stuff!? Anyway, I get two jugs of DEF fluid thinking it is low. On trying to fill it, I didn't get through a half a jug when it overflowed!!! Thinking it was some kind of air blockage, I waited about 15 minutes and tried again. Nope, could not put anymore in. So now, my DIC says that I need more or the damn engine will slowly die on me. The wife is afraid to drive it and I AM dumping it. The owner's manual is worthless. It's back to Honda or Toyota for me! What a waste of money! Chevy should be ashamed. Oh, one more thing, not all Chevy dealers have anyone familiar with this diesel engine.

 

[dieselloverfr06]

Well, here's an update on my '18 Premiere diesel. Picked it up at the dealer after spending almost a grand on a new "particulate sensor" replacement. On the way home, the same engine trouble light came on as they told me it might but then the low "exhaust fluid" warning came on. Now its only been a few thousand miles since since I added some to it. Of course, it goes into this stupid warning system that I only have a few miles to get it refilled. Who are the idiots that engineer this kind of stuff!? Anyway, I get two jugs of DEF fluid thinking it is low. On trying to fill it, I didn't get through a half a jug when it overflowed!!! Thinking it was some kind of air blockage, I waited about 15 minutes and tried again. Nope, could not put anymore in. So now, my DIC says that I need more or the damn engine will slowly die on me. The wife is afraid to drive it and I AM dumping it. The owner's manual is worthless. It's back to Honda or Toyota for me! What a waste of money! Chevy should be ashamed. Oh, one more thing, not all Chevy dealers have anyone familiar with this diesel engine.

Yes Not all Chevy dealers know what they are doing when servicing this emissions system. Plus I am Not At All Impressed with the computers in the car. My dealer is a huge Metropolitan dealer and they work of lots of diesel GM products so they do know what they are doing. Also if you miles driven were low enough it should have been covered under warranty. I had my problem with this system early and they explained to me how to prevent the sensor and the PCV and EGR vales from getting clogged. So I am at 45,000 miles driven since then and everything is working fine plus really great mileage.

 

[tunkertrigger]

Thanks, DL06, I am taking it back to this new-to-me dealer who has been accommodating so far tomorrow morning. I have owned VW and Volvo diesels and had no problems whatsoever with them. I almost invested in MB diesel but maintenance is expensive. Not making the moola I used to. Sooo, I guess we shall see what they come up with and will definitely check on warranty. I appreciate everyone's responses.

 

[dieselloverfr06]

Thanks, DL06, I am taking it back to this new-to-me dealer who has been accommodating so far tomorrow morning. I have owned VW and Volvo diesels and had no problems whatsoever with them. I almost invested in MB diesel but maintenance is expensive. Not making the moola I used to. Sooo, I guess we shall see what they come up with and will definitely check on warranty. I appreciate everyone's responses.

My wife doesn't always drive it for the best mileage but this summer we have been getting 38 to 40 combined metro driving. I do a lot more of the interstate driving when even the dash is telling me 42 to 46. But I gauge it by the calculated mpg after fill up of fuel and I think the latest was about 37. We have gotten 58 on a drive to the North Shore and back which was over 400 miles most of it highway driving. plus mine is loaded with options of which my least favorite is the maps and audio system. it is acceptable but the maps is just crazy and expensive to update. so instead I use Google maps on my large tablet whose screen is more than twice the size of the cars. We have hauled a lot in the car both in volume and weight. My Chevy diesel pickups hauled more but also much more expensive to drive but were less than my 1977 Suburban! LOL! We also had a Cruze diesel car that we both miss that was a real beauty. great mileage and 2 liter power. I called it a sports sedan. Been thinking about buying one used for the fun of it.

 

[tunkertrigger]

I am happy for your success with your diesel. This will be my last post. I sold my Nox to the local dealer after I took it back for the whole DEF debacle I reported ealier. My wife was afraid to drive it for fear of being stranded. The dealer ran all kinds of scans for codes and showed me a laundry list of issues that generated. It would have cost thousands to do everything the codes were revealing. So I just asked if they would buy it. They did. I took a bath on it but it was worth it instead of investing money in it. C'est la vie! Have a great and safe life!