What is your question?
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What is your question?
Three weeks ago service engine light came on and read codes P0171,P0174,and P0442. I bought a new fuel cap and cleaned the mass air flow sensor. The light went off, but came on about a week later. It now reads code P0174, P0442. What is the most likely reason for this issue?
How long has your 2003 Ford Expedition had this problem?
1 month
2 Replies
I'd be surprised if the P0171 was not going to set as well. It would be best to check your fuel trims using a diagnostic tool where you can look at data. You'll likely find that both pre-cat oxygen sensors are acting identically, running lean. Cleaning the MAF sensor is often not helpful. Check the BARO reading using that same diagnostic tool and see if it is reading at the appropriate number for your altitude. If not, it will need replaced, the "Keep Alive Memory" will need cleared, and a drive cycle performed to verify repairs. Other possible causes of both banks being lean would be a a vacuum leak somewhere, such as with the PCV tube -- fairly common with the 5.4L V8's on these vehicles. The P0442 can be caused by multiple components; a fuel cap is a relatively inexpensive guess, but until you hook up a machine that produces smoke/vapor into the evaporative emissions system and see where it leaks out -- you will be continuing to guess.
Additionally - insufficient fuel delivery will cause lean running engine / codes as well. A quality diagnostic scan tool along with fuel pressure testing is imperative!