I've Done All Of The Tests And I Still Have Codes P0171, P0174
So you have done all of the tests, you have researched the codes to death (online and in repair manuals), and nothing you have done or replaced has solved the problem!
Trying to solve P0171 and P0174 DTCs can convert your Ford vehicle into a money pit. To avoid this you need to remember one very important thing:
Be Patient: Whatever part, whether it's an intake manifold gasket or an O2 sensor, is causing the codes hasn't completely fried yet. This happens.
Parts don't always fail in an immediate fashion. So, the gaskets or vacuum hoses or the sensor could seal/work/function/ correctly most of the time, and every now and then they stop doing their jobs. This happens a lot! What can you do about it? Not much but wait till the problem is present all of the time.
Patience is a virtue. If you have checked for vacuum leaks and you have none and you have verified that the fuel Trims are OK (which means the O2 sensors are OK too), then the best thing to do is to wait a few days and retest again. Whatever is failing will continue to fail until eventually the problem will be present to verify it with the tests described in this article.
The important thing to remember, is that you can use your scan tool to check the Fuel Trim values with your scan tool to verify the lean condition (that is setting the P0171 and/or P0174 codes) is actually present.
More Ford 4.6L, 5.4L Diagnostic Tutorials
If you enjoyed and/or found this ‘How To’ article helpful, I have written several more Ford 4.6L, 5.4L specific test articles. You can find them all in this index: Ford 4.6L, 5.4L Index Of Articles
Here's a small sample of the articles you'll find there:
- How To Test The Fuel Pump -No Start Test (Ford 4.6L, 5.4L).
- How To Test The Crankshaft Position Sensor (Ford 4.6L, 5.4L).
- How To Test Ford Coil-On-Plug Ignition Coils 4.6L and 5.4L V8 Engines (at: easyautodiagnostics.com).
- How To Test The Throttle Position Sensor Ford, Mercury, Lincoln 4.6L and 5.4L Engines (at: easyautodiagnostics.com).
- How To Test The FORD MAF 4.2L, 4.6L, 5.4L Round Air Filter Canister Assembly MAF Sensor (at: easyautodiagnostics.com).
- How To Test Ford MAF Sensors Using a Multimeter (at: easyautodiagnostics.com).
If this info saved the day, buy me a beer!
