Codes P0171, P0174 and P1174

Tiny
THEO LEWIS
  • MEMBER
  • 2008 CHEVROLET SILVERADO
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 200,000 MILES
The engine seems to run fine.
Sunday, April 10th, 2022 AT 1:21 PM

1 Reply

Tiny
AL514
  • MECHANIC
  • 4,692 POSTS
Hello, is this a gas/ethanol engine or just gasoline?
These codes p0171 and p0174 are both bank 1 and bank 1 lean codes.
The p1174 is an imbalance in the fuel trims bank 1 compared to Bank 2.
These are known for vacuum leaks from the Intake manifold gaskets. If your fuel trim numbers are all positive numbers, which I think they will be, that means the ECM is adding fuel to the air/fuel mixture to compensate for extra air coming in somewhere. If you look at the live data on your scan tool you should write down what the fuel trim numbers are at Idle and at 2,500 RPMs, if the fuel trim numbers go back down towards 0 at higher RPMs, then most likely this is a vacuum leak.
Low fuel pressure can cause a lean condition as well. The fuel trim numbers might actually get worse at higher RPMs if it's a lack of fuel pressure/volume. I use a smoke machine to find difficult vacuum leaks but there are different methods also, below is a guide to vacuum leak testing.
But look at your live data, take a picture of all the readings at Idle and at 2,500 RPMs. That way we can see what all the sensors are doing.
A mass air flow sensor that is reporting incorrectly due to a little carbon build up on the sensor will cause fuel trims to be off. But I would look for a big vacuum leak first.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

https://www.2carpros.com/articles/repair-lean-mixture-codes-p0171-or-p0174-on-some-manufacturers

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator
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Sunday, April 10th, 2022 AT 1:52 PM

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