Error Code PO174 System too Lean (Bank 2) 02' Yukon

[02YUKON_MN]

So I have a 02' Yukon that just rolled over 110,500. Just changed my pinion seal and oil/oil filter the other day which I think is completely unrelated to the issue.

My "Service Engine Soon" came on about 4 days after I changed my pinion seal and oil. When it came on I was driving 60 down the highway with about 1/2 tank of gas- just before that I accelerated at the stop light and felt a slight flutter/hesitation. It only happened that one time. I drove it with the light on for 2 more days- probably 50 miles just to work and back. Engine idles fine, starts great and accelerates just as it should. As I'm driving it to my friends house to hook it up to a reader the light magically turns off. We hook it up anyways and it threw the code PO174-System to lean (Bank 2) under the troubleshooting section. I cant get the service light to come back on now.

I am thinking that I filled up at a Costco with 87 and may have been some bad gas. Never put E85 in it but its a 5.3 with that can take flex-fuel.

From what I've read the possible problems that could be causing it to throw this code are Vacuum leaks (Intake Manifold Gaskets, vacuum hoses, PCV hoses, Mass Airflow Sensor (MAF), Plugged Fuel Filter or weak Fuel Pump
or Plugged or dirty Fuel Injectors. Any others I'm Missing?

Is there any particular order anyone thinks I should check these before I just go buy and replace.

I've changed my plugs and wires about 10k ago as well. Thanks!

 

[clandr1]

I wonder if your O2 sensor on that side is just going bad? I'd drive it normally and see if the CEL comes on again.

 

[T. Bishop]

I have very similar problems. It stumbles at idle, but seemingly runs fine. The CEL flips off briefly but came back on. Rather than throw parts at it, I just paid a dealership $100 to diagnose everything.

They very confidently recommended a new intake gasket and fuel pump replacement. He saw vacuum loss and 7psi of fuel pressure (not experienced enough, but that just seems way to low to even run??). I am midway through a fuel pump/intake gasket replacement. We'll see if those are the culprits, but at least it will be peace of mind to have a new fuel pump.

 

[02YUKON_MN]

I wonder if your O2 sensor on that side is just going bad? I'd drive it normally and see if the CEL comes on again.

Thanks- I plan on it. I'll probably pull it off and test the sensor to see if its bad before replacing