Skip the auto shop - Our mechanics make house calls

Q: I keep getting OBD-II codes P0171 and P0174

asked by on

I keep getting the P0171 and P0174 lean bank 1 and 2 code. When I fogged the intake the only smoke came from the press cap on the idle air control valve, I did this on my 02 F-150 with a 5.4 no smoke. When I say press cap I mean the cap on he valve that looks like a freeze plug crimped over the valve. Is this normal, since taping around the valve I haven't had the check engine light for over 300 miles.

My car has 203500 miles.
My car has an automatic transmission.

A: Since you have codes that both banks are le...

Since you have codes that both banks are lean then the problem will most likely be from air entering the intake manifold after the mass air sensor. The idle air control valve should not have any air leaks from the valve and may be contributing to the codes you are getting. It would be recommended to scan the computer data to see if the mass air sensor is registering the correct barometric pressure reading. This reading should show the proper pressure for the altitude your vehicle is at. If the data is reading that you are above more than 1000 feet more than what you are at then the mass air sensor is causing the codes and the mass air sensor needs replaced. The mass air sensor can be damaged by an air filter that is the oil bath type and should be the dry type filter. Replace the air filter if it is incorrect type or is dirty restricting air flow into the engine.

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・Save up to 30%

Get a quote

What others are asking

Q: Misfire in cylinder number 8.

Hi there. The issue could be the spark plug not firing on cylinder 8, the fuel injector not atomizing on cylinder 8, or there could be a burned valve or a burned head gasket. Check the spark plug on cylinder...

Q: Puddle of fluid

If the fluid is pinkish or red, it could be automatic transmission fluid. A certified technician from YourMechanic could perform a leak inspection and let you know what the required repair is. The temperature fluctuation you refer to is probably...

Q: Check engine light

Hello. P0171 is the trouble code for a lean condition at bank 1. This can be caused by a wide variety of issues, primarily issues with the engine management or fuel systems, and therefore can sometimes be difficult to diagnose....

Related articles

P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
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...