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A. Penland
A. Penland, Ford Senior Master Technician, ASE
Category: Ford
Satisfied Customers: 6667
Experience:  ASE Master Certified, ASE Advanced Gasoline Engine Performance
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2002 Ford F150: service engine light..actron obdii reader..p0171

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My service engine light soon came on in my 2002 Ford F150, approx. 75000 miles on vehicle, removed codes, they reappear usually within a couple of days. Used an Actron OBDII reader, god codes P0171 (system too lean bank 1) and P0174 (system too lean bank 2). Also, P1131 and P1151 (Manuf. Control Fuel Air metering. What do these codes mean, what is a possible diagnosis? Vehicle seems to be running OK.
HiCustomer Thank you for asking your question on JustAnswer. The other Experts and I are working on your answer. By the way, it would help us to know:

-What type of engine is in your Ford?
-What have you already tried?

Thank you again for trusting us with your problem. Please reply as soon as possible so that we can finish answering your question.
Customer: replied 8 years ago.
V-6, I believe it is 4.6 liter
V-6 is a 4.2 liter. P0171, P0174 are lean codes. P1131 and P1151 are codes saying lack of 02 sensors switching. These codes are caused by unmetered air entering the engine through a vacuum leak. Check the PCV hoses going to the engine. They tend to get oil in them and the break down and crack and colapse causing leaks creating your codes. The 02 sensors are not bad. They are just sending info to your computer telling it what they see.
Customer: replied 8 years ago.
are all 4 codes caused by the vacuum leak? I will look for the leak, as recently, I'll say in the past couple of months, I get a high pitched whistle from the engine compartment. I told my daughter that my engine was haunted, because I can usually rely on it to make the noise in front of a funeral home that we pass about 3 miles from our house on our way to church. It is very intermittent. But it seems to make sense. So if I fix the leak and remove the codes then it will most likely be fixed?
Yes they are all caused by a vacuum leak. These 02 sensors only minitor the exhaust and relay the info to the comuter. Look for the whistle noise. It will point you to the vacuum leak. Possibly a PCV hose.
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