My Silverado is a 2015 with about 72k miles. A couple of months ago my check engine light started coming on. I noticed a couple of things. It normally did it when I would sit with the truck idling for extended periods, like at my sons football practice. I am not noticing any different odor coming out of the exhaust. When this happens, my stabilitrac light usually illuminates. I also notice when it happens, my shift is rather hard. Not clunky or anything, but almost like it is shifting at high RPMs except that the RPMs are normal. More like it kind of surges and shifts hard. It will also run on, or continue to idle/spit/sputter for a couple of seconds after the key is turned off. Normally the next day or two days later the engine light is off and everything is fine until i set and idle for a long time again. I checked and have a P0175 and P0172 code. I know that can be a host of possible issues but I wanted to throw this out here in hopes that someone might have a good idea of where to start. I would love to be able to fix this myself instead of taking it to the shop.
Thank you!

 

Those P0172 and P0175 codes are saying your engine is running too rich, on both banks. So essentially after idling for a while your engine is loading up with fuel somehow. I imagine you probably smell some gas or very rich exhaust?

Easiest thing to check is your air filter - aside from that I think the easiest route to figure it out would be to get a code reader/scan tool with engine data, so you can watch the fuel trim numbers and engine sensors to see what doesn't look right.

 

if you have a flex fuel vehicle; check the alcohol content sensor reading. if its askew it will cause the fuel trim to go rich. if you don't use flex fuel the sensor should be reading 10% or less. if it over, reset the OH sensor with a scan tool.

 

I went ahead and changed out my air filter, and yes, it def needed it, and went ahead and cleaned my MAF sensor while I was at it. Afterwards,I hooked up my scan tool and noticed that my SHRTFT1 is reading -2.3 and the LONGFT1 is reading -32.0
What other values should I be looking at and do those two readings tell me anything?

 

It is not a flex fuel vehicle.

 

Your Long Term Fuel Trim at -32 is what is triggering those fault codes. The system is taking away 30 percent of the fuel trying to balance the mixture, and that's as far as it can go. It sounds like something is leaking gas into the engine, usually an injector will be isolated to a cylinder or at least one bank or the other. I believe some of these engines had some high pressure fuel pump issues leaking?
Other readings you can look at are the MAF number, should be close to 0 with engine off, 20 or 30+ when stomping on the throttle. And all of the temperature readings to make sure they make sense.

 

What worked??

 

My truck is currently doing this same thing. 2015 with 86K. Ive cleaned MAP and changed filter. Still not resolved. I was fixing to order a HP pump. Did you get issue resolved and what was the problem? Thanks.

 

Anybody know the fix?? 2015 gmc sierra 1500 with the 5.3 with 71,000 miles, went on a 2 hour car ride, got back and idled for about 20 minutes, shut truck off for about an hour, started up no problem and once moved my stability light came on then went off, hit the first red light and the stability light came on and then off and then the engine light came on, up shifted hard and down shifted hard, has P0172 and P0175 codes active, any help would be appreciated

 

what worked?