Skip the auto shop - Our mechanics make house calls

Q: Still getting error codes

asked by on

I just changed the mass airflow sensor and I am still getting codes P0171 and P0174. I'm thinking it could be the O2 sensors.

The codes you have for your GMC Yukon, p0171 and p0174, are informing you that the engine is running lean. This means that there is unmetered air entering the engine after the mass airflow sensor and is disturbing the air/fuel ratio needed for your Yukon to run properly. Typically when both of these codes are present, it is a strong indication that the intake manifold gaskets have a vacuum leak. Attaching a vacuum gauge to the engine while it is running will quickly tell you how severe the vacuum leak is. In order to pinpoint the source of the vacuum leak, a special smoke machine needs to be hooked up to the engine. Typically, this is done right at the throttle body. Smoke will fill the intake manifold and vacuum hoses and once it finds a leak, smoke will seep out of it and will be visible to see.

I would recommend enlisting the assistance of a certified mechanic to come by and inspect your GMC Yukon. They will have the speciality tools and experience needed to determine exactly why your Yukon is running lean. They will also be able to perform the repairs necessary to eliminate the vacuum leaks and get your GMC running like a champ.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: My 2000 ford expedition is showing 0171 and 0174 codes do you have a estimate to fix?

The codes P0171 and P0174 point to a lean condition picked up by the oxygen sensors in the vehicle's exhaust system. Since there is a warning from both banks, it may be safe to say that this is could be...

Q: Flashing service engine light

If the check engine light starts flashing it can be for many different reasons and all of them can be serious causing the catalyst to get damaged and exceed emission out put from the engine. You could have a misfire...

Q: overheating problem

Thanks for writing in about your Hummer H2. Let's cover the basics of diagnosing a overheating issue. First, verify the actual temperature at the thermostat housing. Cooling system (and cap) has probably been pressure tested by now. If it tends...

Related articles

Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...