my 98 seville when i first got this car i had this code (P0174). I know that this is not caused by a bad O2. i had to replaced the O2 sensor cause it was bad though. After doing that i never got the code unless i was on a highway for about 30 miles then it would set the code. So i checked to see what else it could be and i know it can be MAF,vac***e leak, fuel filter, intake gasket. i ruled out the gaskets since i replaced all of them. I dont see any vacuum leaks since most of the hoses are in good shape with no cracks or brittleness. Im not sure how to test the MAF but i would suspect that would usually set both P0171 & P0174 at the same time. i was wondering if any body has had this same issue before and knew what may have been the cause.

 

also i forgot to metion the exhaust has a nasty smell from running lean. and i can barely get 13mpg in town driving with no highway driving.

 

Have you checked for an exhaust leak on that side? That could create a "lean" condition signal at the HO2S....

 

i have done some more investigating as to when this code pops up and the Sevice light comes on. I noticed while driving down the highway for about 30-60 miles at 60-70mph and the RPMs are around 2k while on a flat road with no major hills. This will cause the CEL to come on and Shows only the P0174. Not sure why only one side is being leaned out but i cant seem to figure it out. i cant see or hear any vacuum leaks and the exhaust seem to be fine too. Ive been chasing this issue down and am scratching my head.

 

all u can do is follow the logic.
lean equals more oxygen or less fuel.

unless u got a faulty computer, vacuum leaks and intermittent fuel injectors be high on my list of items to check.


.

 

You need a scanner or access to one, so O2 data can be monitored. When lean codes set computer adds fuel to try to get to normal O2 reading. If it can't set code. MAF is another possible cause, without scanner it guessing with parts (your wallet)