Q: Getting codes P0171 and P0174 with Service Engine Light on.

asked by on January 04, 2018

Last week I noticed my Service Engine Light came on when it was really cold outside. I borrowed my buddies OB2 scanner and it came back with codes P0171 and P0174. So I researched on google and started eliminating items it could be. I cleaned the air filter, cleaned the MAF sensor with MAF cleaner, replaced the PCV elbow hose by the PCV valve as it had a small hole in it, and put a new fuel filter on. Reset the light and it came back on this morning a day later. Engine idles great, starts right up when you start it, and no acceleration issues that I'm noticing. Autozone said it's my fuel pump but that doesn't make any sense to me as a bad failing fuel pump your car/truck would be hard to start or not start at all and you would have drivability issues which im not having. Anyways, any help would greatly be appreciated. Thanks! :)

My car has 219000 miles.
My car has an automatic transmission.

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P0171 and P0174 say the system is too lean on both banks. That means that whatever is causing the problem is common to both sides. The first thing to check for is air leaks, but it sounds like you have already been there. Doesn’t hurt to look again though, I’d say 8 out of 10 of the P0170’s that I fix are air leaks. As for the fuel pump, you are half right. But there might be a problem with fuel pressure. Your truck probably has a pump in the tank with an integral pressure regulator. At 200 thousand miles that is possibility. The way to check this is to do a fuel pressure test. If you decide to get some help with this, contact YourMechanic. They will send a technician to your home or office to check out your ford and let you know what is the solution.

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