Two of the most common trouble codes with the GMC Yukon are P0174 and P0171. Both of these codes reference a number that is given to you when you plug your truck into a OBDII scanner. P0171 and P0174 occur when the air/fuel mixture on the truck gets too lean. They are both thrown when the oxygen sensors detect that there is not enough oxygen in the exhaust. The engine then makes adjustments to compensate and throws these codes, which trigger the service engine soon light.
P0174: Fuel Trim System Lean Bank 2
P0171: Fuel Trim System Lean Bank 1
When these codes both appear at the same time, it is more often than not the intake manifold gasket that is the cause of the problem. It can be other things as well, but the intake manifold gasket is a great place to start.
Yukon P0174 and P0171 Code Defined
P0174 and P0171 are OBDII trouble codes. The code technically stands for:
Fuel Trim System Lean Banks 1 and 2
These codes are thrown when the oxygen sensors detect that there’s not enough oxygen in the exhaust system. This is commonly referred to as a “lean” condition.
The vehicle’s ECM will add more fuel to the mixture in order to bring the air fuel mixture where it needs to be for optimal combustion. It also throws the codes to let you know that it has done this.
GMC Yukon P0174 and P0171 Code Symptoms
The P0171 and P0174 code on a GMC Yukon will often be thrown if the fuel injection system is not operating properly. Typically the code will be triggered by a lean condition in the engine.
There aren’t usually any drivability issues associated with these codes. For most people the first sign that anything is wrong at all is the service engine soon light coming on.
Here are the typical symptoms that something is wrong when you have code P0174 and P0171.
- Mileage- may or may not suffer depending on how much the air fuel mixture has changed.
- Misfire– If the air fuel mixture has gotten too far from factory specs, this can cause the Yukon to misfire.
- Idle Issues– With the air/fuel mixture altered, the vehicle can idle erratically as the computer compensates to keep the engine running.
GMC Yukon P0174 and P0171 Causes
There are many things that can cause these trouble codes on the GMC Yukon. The most common problem is far and away the intake manifold getting a vacuum leak.
- Vacuum Leaks– With the GMC Yukon, the most common cause for the P0174 or P0171 code to show is a vacuum leak. Take a look around and see if you can find the vacuum leak. Here’s a great YouTube video on how to find a vacuum leak.
- Mass Air Flow Sensor– The mass air flow sensor calculates the volume of air entering the engine. If it has gone bad, the air fuel mixture will be off and the P0174 and/or P0171 codes will show.
- Bad Fuel Injectors– If you have one or more fuel injectors that have gone bad that can certainly cause the air/fuel mixture to go bad.
- Fuel Pump/Fuel Filter– Today’s modern fuel injected motors need a lot of fuel pressure to atomize the gas properly. If the fuel pressure is not as high as it needs to be this atomization doesn’t happen properly and the optimal air/fuel mixture isn’t achieved.
Here’s a great YouTube video on the subject. This guy really gets into the problem, and can really help you find the cause of the trouble codes with the Yukon.
Good luck figuring out what is causing the P0171 and P0174 trouble codes with your Yukon. If there are any inaccuracies, or anything that you feel could improve the article, please feel free to comment or message. Thank you.