P0174 with no leaks

Looking for some help. I have a P0174 lean bank 2 code. Took it to stealership, they replaced bank 2 AF sensor. $500 and one week later, the code has returned. I cleaned the MAF and did throttle body while i was in there. Still have code. Paid shop to do Vac and exhaust leak test, they couldn't find anything. They also checked fuel system pressure and said it was fine. They suggest replacing the MAF sensor and going from there.

Truck drives fine overall, but has a rough idle and when i start it, black wet soot comes out exhaust. Also had some black smoke while pulling a hill a few weeks back. Exhaust smells very rich in fuel and obv fuel economy is terrible.

Nest Step Suggestion?

 

Maybe call the dealership and ask them, what led them to diagnose the AF Sensor as faulty.
If it’s back on so soon, I would at least ask the dealership to inspect the previous repair.

Seriously, for $500. I’d at least ask for help. That’s a lot to pay.

 

Get a capable scan tool and monitor your bank 2 rear O2 sensor and compare it to bank 1. We've seen faulty rear O2's cause A/F ratio sensor codes.

The torque app with a blue tooth dongle (I use the Kiwi) will do this for you. You can graph all 4 sensors.

It's a lean code, so don't rule out exhaust leaks right around the A/F sensor or the rear O2 sensor. This can skew the readings. The computer is falsely adding fuel, that's why it's running rich.

A MAF usually won't fix a single bank issue.

You could also have a leaky injector on that bank - and NO it won't cause a rich code, the O2 sensor doesn't detect oxygen in raw fuel.

 

I took your advice and went back and complained. Theyre going to run further Diagnostic at no charge and we will go from there.

 

The scan tool i have doesnt show that info, and yes it would be very beneficial. My own person diagnosis is that it is the bank 2 o2 sensor causing the a/f sensor codes. A local shop said they'd check exhaust and vac leaks as well as fuel system pressure for $80. They found no leaks and said try replacing MAF. But i agree with you, that it makes no sense to only have bank two codes and it being the MAF. So ive ruled that out, and told the shop id "think about it".
Injector is my second theory for the issue. I put a bottle of injector cleaner just to see if theres any difference, after burning half a tank, i think it has helped. Went from rough idle 95% of the time, to rough idle 15% of the time. My only concern is the dirty injector is a result of the excess fuel being dumped in because of the o2 sensor, and is not the actual cause of the problem, more so the result.

Went to the dealership again and asked "was the AF sensor ever tested, or just replaced because of the codes?". He defended why the replaced it for a while, but when i just kept bringing up the injectors and o2 sensor as the reason for those codes, he caved and said they would look at it again for free. so we will see what happens from here.

Ive read many threads of people having similar issues, but no one actually finishes it with how they fixed it. So, i will at least provide that. Thanks for the input.

 

Please keep us updated.
It helps the community tremendously when people report the diagnosis AND THE FIX.

Hopefully you get this fixed soon.

 

Finally made it back to the dealership. They basically said everything looks normal. Fuel pressure test ok. No vacuum leaks and trim levels all look normal. Truck operates at almost 100%. But the p0174 code did come back on during a 6 hour road trip. Then quickly shut off during city driving. So im going to use another bottle of fuel injector cleaner in a couple weeks as that made a huge difference.

My suggestion to others: If you have a lean bank code and a rough idle. Try this $7 bottle of injector cleaner before you start replacing sensors. As im fairly confident that sensor did not need to be replaced and was a huge waste of $500. The product that worked for me was STP super concentrated fuel injector cleaner. The all purpose injector and fuel system cleaner did nothing.