My truck is 2003, V6, 4.0, SOHC. The check engine light recently came on--the code scan showed PO 171, System too lean (bank 1) and PO 174, System too lean (bank 2). My question is, what ailment in the engine would cause these readings and what can I do to fix it (short of taking it to a mechanic)? Any suggestions/comments will be appreciated.

 

Sounds like your O2 sensors need to be replaced.

 

it is not the O2 sensors. maybe MAF, vacuum leak,

 

I agree, it's more likely a vacuum leak.

The SOHC is prone to developing holes in the PCV elbow hose, allowing unmetered air into the upper intake, and hence lean codes.

https://www.ford-trucks.com/forums/6...1-codes-3.html

 

At about 58000 miles my 2003 3.0 V6 showed this code. After several resets and re-cycles. The dealer flashed the computer with new software. There had been two updates. Now at 78000 miles the problem has not returned.

 

my mustang had the same problem. it was a loose hose clamp between the maf and throttlebody

 

I am with powerstroked on this one do not but new o2 sensors. Vaccum leak is most likely to be the problem. Also if you cant find it, take some carb cleaner and pinpoint shoot some at the base of the intake and lower plenum and listen for a change in idle. Thats what your mechanic is going to do first.

 

Everyone--I appreciate all you who posted comments and made suggestions--it turned out to be a vacuum leak in one of the PVC hoses. A few dollars for the rubber elbow at Autozone and it's good as new. I've run it several days now and the codes have not returned. Also cleaned the MAF while I was at it. Many thanks.