2015 Malibu with erroneous P0171 code
 

I've got a 2015 Malibu 2LT, 2.5L DOHC, 4-CYL with 64,400 miles. When the Check Engine Light came on, the engine was running fine, nothing unusual. I brought it into the dealership, they determined it had a P0171 code (no other codes). They spent between 5 and 6 hours trying to determine the cause and never did. I remember one of the service writers showed me what appeared to be service bulletin for P0171 and other codes which went on to talk about rocker arm issues, etc. (I may not have all the details correct on that, but I believe that's what was said.) My engine sounds fine and didn't seem to be related to this. I was told by the service advisor that it could be a bad sensor giving a bad reading as well. They reset the Check Engine Light and released the car to me. I would think that over 5 hours of work should be enough without needing more time on this. Luckily, I wasn't charged since they couldn't come up with a solution. I was told if the Check Engine Light comes on again, to bring the car in again and they would continue to work on it.
Engine continues to run fine. Has anyone seen erroneous P0171 codes? The report I got from the technician follows:

Verified customer concern. Upon inspection found DTC P0171 mixture. Inspected vehicle further to isolate cause of lean fuel mixture. Was unable to verify lean fuel mixture with visual inspection, smoke test inspection. In order to further inspect, tech requests additional diagnostic time to isolate cause of stated issue. Customer declined at this time.

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I'd clean the Mass Air Flow sensor (MAF)The mass air flow sensor calculates the volume of air entering the engine. If it has gone bad, the air fuel mixture will be off and the P0171 code will show.

Thanks. You'd think there would be symptoms like the engine running rough but the engine runs smoothly.

is this engine a gas direct injection or injectors in the intake manifold?

Can't answer that. The engine spec just reads this:

Engine, EcoTec 2.5L DOHC
4-CYL DI W/WT, Intake VVL
& Auto Stop/Start

Yes it is. He has the same GDI 2.5 liter non-turbo engine I have in my 2015 Chevy Malibu.

Yeah, I know, Deepening on what it is, I've seem it before, With the MAF ive seen dirty ones that didn't throw any codes at all. Kinda weird..

would need to know what rpm the code sets at.
hopefully, they checked fuel pressure, The smoke test was done to find a vacuum leak but it can be checked faster using other methods.
the older di engines had a fuel leak into the crankcase at the high pressure injection pump. Any smell of fuel on the engine oil dipstick.

Finally solved this issue. Took the car into Tires Plus, they couldn't solve the problem either but they gave me their list of possible culprits for code P0171 and one culprit was "Fuel Quality" I went to a different gas station and put in some gas (same octane) and within a day, the check engine light went out. I'll add some fuel injector cleaner to the car as well.

It turned out that even after filling up with a better grade of gas, in January 2020 the dealership was able to isolate another occurrence of the check engine light being on to a faulty fuel pump. They replaced the fuel pump. That seemed to take care of that issue for a while. Now, I notice that when the outside temperature goes down into the 40s, the check engine light comes on. I've decided just to clear the light myself after verifying the P0171 code is still coordinated with it. When the temperature warms up, the light has been staying off. At this point, there's no way I want to spend hours in a dealership with no permanent solution when the real cause might be a software glitch that will only be fixed in a later model.