I have a 1999 Mercury Mystique with 75,000 miles on it. For the second time in a bout 6 months the check engine light has come on. The first stime the light went out after several days. This time I had a local auto store check the codes. The code came up PO 171 7 PO 174 - Right and Left engine banks too lean.
Any idea how to correct or what to address first? I was informed this could me o2 sensors or the Mass Air Flow sensor. Which ones or all?
Most likely cause of the code is one or more of the following....
Dirty air filter, loose oil dipstick, dirty/defective MAF, dirty injectors, vacuum leak around the intake manifold, a loose vacuum hose, evaporated emmissions purge control valve could have a wire connector disconnected, or possibly bad O2's.
Go with the easy things first. Check the Airfilter. Check the dipstick is seated. Look at that MAF and see if it needs a good cleaning or is damaged. Check those vacuum hoses. Check the injectors to make sure they are in good condition.
Once you have checked the above items make sure you have the DTCs cleared that way your CEL goes away. Drive for 30 miles and if the CEL comes back you can rest assure that it is most likely the O2s. But as I have said....check the simple, easy and cheap things first.
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