i've got a 1998 mustang with the 3.8L. the check engine light came on and i read the codes that came up which were PO1151 and PO174. i read that the 1151 code means it upstream O2 sensor on the driver's side. do i need to replace both sensors or just the one? has anyone else dealt with this? i would appreciate any advice

 

The 174 code is definitely an o2 sensor code. Replace both o2's before the cats, or just replace all 4. GL