Help!! I'm going crazy.
 

I have on 08 LTZ with the 5.3L Flex fuel. We have been trying for months now to figure out why it keeps throwing codes p1174 and p1175. Here is a list of everything done, my mechanic is cursing this thing....just wondered if anyone here had any ideas.
All 02 sensors & spark plugs
Fuel pump assembly
All 8 injectors
Mass air flow sensor
Oil pressure sensor
Checked for intake and exhaust leaks and fixed
Called gm to see if there was any updates for the computer
Checked to see if fuel pumped is putting out what it should it is.
I have a chip that is a code reader, which says I have a lean condition in bank 1 and 2
Should also mention there is an extended crank to start sometimes, but only after you drive somewhere and it sits for a bit, then you come back out to start it. If you step on the gas it fires right away which makes no sense with fuel injection. First start in the morning is always fine, fires right away. Since most of these repairs were done, there is no longer an issue with it being sluggish, and is shifting the way it should, before it felt like a boat anchor and I really had to mash on the gas pedal to get some giddy up and go.

Pressing the "gas" pedal opens the throttle so maybe it's a flow problem. Did you check if the cat is clogged?

I tried to research your codes, and I could not find anything in the p1100 range. I did find these power-train related codes that might be useful, if what you posted was typos regarding your error codes. From your description of things, maybe it is time to find another mechanic, You have spent a LOT of money throwing parts on a problem in what is called the "poke and hope" method. An angry mechanic "cursing" takes out his frustration and aggression on the vehicle, and in looking at the codes you have posted, it doesn't look like the scanner the mechanic is using is doing effective diagnostics. If you have a rich or lean condition, the O2 sensor reports that as a voltage that is outside of a pre-programmed range in the PCM. A rich condition is voltage too high, and a lean condition shows voltage too low. A real-time data scan needs to be done with the engine running to see what is happening as far as voltage switching and fuel trim. From looking at the list of codes I have supplied, I would think your scanner results would have shown more codes.

P0163 O2 Sensor Circuit Low Voltage (Bank 2 Sensor 3) (LEAN)

P0164 O2 Sensor Circuit High Voltage (Bank 2 Sensor 3) (RICH)

P0170 Fuel Trim Malfunction (Bank 2)

P0171 System Too Lean (Bank 2)

P0172 System Too Rich (Bank 2)

P0173 Fuel Trim Malfunction (Bank 2)

P0174 System Too Lean (Bank 2)

P0175 System Too Rich (Bank 2)

You might go to https://www.vehiclehistory.com (thanks to benzo for the link) to see if any recalls are applicable to your vehicle.

Keep us posted with your progress, and because i didn't see it in your post, what kind of condition is your air filter. Maybe you have a bird or mouse nest in the air intake.

I found them with a quick google search.

https://www.engine-codes.com/p1174.html
P1174 - Fuel Trim Cylinder Balance Bank 1
P1175 - Fuel Trim Cylinder Balance Bank 2

My mechanic is actually top notch. Most honest tell it like it is guy you could find. And definitely not throwing parts at it for no reason. That's exactly what he has been trying to avoid doing. Even GM has been stumped on this. I can assure you those are valid codes....as said in another reply, just Google them.

Golly, I have to admit i didn't utilize a specific "p1174" or p1175" on Google. I went here: https://www.outilsobdfacile.com/data...-code-obd2.php under a Google search for OBD CODES. So apparently that web page is incomplete, It only provides generic codes. Thanks moutainmanjoe for bringing me up to speed on this.

If you are getting fuel trim codes then maybe the fuel regulator isn't bleeding off fuel pressure correctly. I guess your "top notch" mechanic will do a far better job for you than someone you ask for free advice from. To my mind, if he was that good, you wouldn't be on an on-line forum looking for information to "help" him, or you. 2 posts in this thread indicates you aren't here for the fellowship.

How much did FOUR O2 sensors cost you,or even 2? That mis-diagnosis didn't red-flag you? It might have helped make the car run better, but it didn't fix the problem.

An oil pressure sensor? How much was that? Can you explain to me how a p1174 or p1175 code led to that replacement decision?

Has the fuel filter been changed? You didn't mention that. Maybe it is clogged.

I worked in an oil-change place, we would find animal nests in the air cleaner box. You didn't mention that you checked on that idea.

You also didn't mention how many miles are on the odometer. Have you owned the vehicle since new?

But I digress: I worked at a high-end used car-dealership as a mechanic. We had a used Ford Interceptor come into the shop after the detail shop had gotten done getting it cleaned up for resale. The check engine light was on. The first mechanic that worked on it believed the O2 sensors, for whatever reason, were the problem. ALL FOUR OF THEM. After that huge investment in parts and labor, THE EXACT SAME CODES CAME BACK.

That mechanic LOST THE PRIVILEGE of working on that car. He was honest. He was sincere in his belief. That didn't matter. The mechanic that FIXED the problem traced it back to water that had been sprayed into an area that held the ECM-PCM and had water-shorted the wires.

O2 sensors can be removed and tested to verify they are bad. The mechanic in my shop case didn't bother to do that, and apparently neither did your "top-notch" mechanic before he did the work and presented you with an invoice.

It seems that if specific GM codes are showing up related to fuel trim, that the generic OBD codes that I listed above would ALSO be showing. But what do I know, Free advice is either price-less or worth less than that paid for.

If Googling is what you suggest I should do, I would suggest you take your own advice. I'm done.
/end rant

https://cimg0.ibsrv.net/gimg/chevrol...46a2901e88.jpg
Found in the air filter plenum nieghbor's dad's silverado.

<SLAM> I'm back. Mice picture, kevinkpk. Looks like about two years worth of birds. Did anyone ever figure out what kind of feathers were in the nest? It proves my point. Maybe what we are dealing with here is an elderly lady who doesn't drive her car much I have a video around here, somewhere of a similar finding, . . . rummaging around, . . ahhhh, here it is:
In that case, the truck had sat for 2 years in Georgia parked next to a creek. Mice under the seat, mice in the air-box, mice under the hood, and at least one snake under the hood chasing the mice.

Maybe there are chewed wires under the hood of the car. Maybe a squirrel decided to gnaw through some wires, so that they are now shorting to ground. Feel free to share these free ideas with whoever you think will benefit from them.

As far as your having to push the gas when the engine has done a heat -soak, it is possible the PCM is compensating for a lean reading coming from the fuel rail p1174 and p1175 signals and has ordered more dwell time to the injectors as a result That would create an over-rich condition in the combustion chamber which would require you to open the pedal to clear the flood. It may be a fail-over provision in the PCM and another way to warn you car is on the way to the junkyard unless you fix it.