Apparently I bought a dud. Any help would be very much appreciated

Carmen · January 2, 2024

So. I bought a 2014 gmc sierra. Have had nothing but issues. Drove it 5 times and bam. Transmission went. Long story short I also know this guy who had it before was not very good with electrical. So my mechanic said. I've had a p2099 code off and on for almost a month.. drives horrible and getting a wonderful 8 mpg. Today another code popped up p0430. I been trying to figure this out and fix it myself because I'm still paying it off and not making headway when paying for everything 3lse it needs.

asilverblazer · January 3, 2024

Its running too rich and killed the catalytic converter. You need to start diagnosing why it isn't able to correct the fuel trim to what it is supposed to be.

Your mechanic says the previous owner wasn't good with electrical... sounds like something is screwed up. Why didn't the mechanic fix it?

To provide further help we would need more information... any modifications to the vehicle, what all has been done to correct the issue, maintenance and vehicle history, engine size, mileage, drive train, etc.

Carmen · January 4, 2024

The mechanic did fix the issue that I was having at that time. My truck has 180000 miles on it. 5.3 v8. I did fuel treatment, changed air filters, cleaned mass airflow sensor. Put a new transmission in it. This is the 3rd one for this truck. As for modifications I am not sure what else he had done to it.. said rear window didn't work and wasn't sure why. I looked into it. Well he cut the wires off going to it. Haha good reason.

I am afraid I do need a new catalytic converter. I'm just trying to try every other option first .

diyer2 · January 4, 2024

High mileage vehicles is a big risk.

asilverblazer · January 4, 2024

At most, this truck should be on its second transmission.

Why so many pre-mature failures?

Your options should be to fix the cause of engine running poorly. Replacing the catalytic converters before that would be a waste.

Since the truck has been seen by a mechanic - was there any kind of diagnosis or recommendation regarding why the truck is running too rich? Further, if it is indeed running this poorly, the engine should be throwing codes, so why is it not?

I would suspect the previous owner has done something to prevent the truck from actually seeing how poorly it is running and thus it can't correct it, are the upstream O2 sensors intact and performing correctly? Your mechanic should be able to easily verify this and if not - find a new one. So far from what you've said I already have my doubts about this mechanics ability.