i replaced the upper 02 sensor just a week ago and now the check engine light is on again, any help? its a 2002 lancer and someone said i could have a blown head gasket but i dont believe it? where do i go from here? the engine runs fine so i dont know what to do next thanks for any help

 

go to autozone and have them scan the code

 

my husband has the scan tool and it shows the same code.. upper 02 sensor which i just replaced a week ago and now the check engine soon light is on again and i dont understand why?

 

do you know the exact code number. Generally that means that the O2 sensor is picking up fumes above the emission expected. So you are getting excess emission from something else not working. It may be something as simple as the EGR valve being dirty or clogged. I highly doubt its a head gasket unless you are losing coolant, smoking out the exhaust, and overheating, haha.

 

It could be the warmup converter that is made onto the exhaust manifold. There was a recall some time back to reflash the ecm. If it wasnt done you could burn out the Cat. Im not sure if an 02 was part of the recall or not.