Celica Forums General Discussion Exterior Check engine problem pls help

i have a serious check engine light problem. I hope somebody can help me . Here is the story

I have 5zigen catback exhaust system on my gt, everything was fine until las month. I was driving on highway and speeding around 80 mls , then the check engine came on and went to a mechanice and he reset the ecu and said it is fine. When i use my car in the city no check engine light because i am not driving over 50 but when i speed up , it lights on . So , i went to a different mechanic and he said we have to replace the oxygen sensor and he replaced it after 2 hours , i wanted to try the car and speed up and it came on again . He told me to go the dealership but i know if i go to dealership , they will start to complain , you have aftermarket parts on ur car etc etc . The code is 171 for the check engine light , anybody has any idea what to do ? i am thinking to change the whole exhaust system but it is weird why the check engine comes on when i am speeding and it doesnot come on when driving normally ? thanks for any help

I seriously doubt it has anything to do with your exhaust... do you have a cai?

mine does this too..

try cleaning da MAF sensor thats a common problem i learned it the hard way...$110 for the dealer to tell me that the maf sensor was dirty

i have an aem 2 nd gen Intake but havent installed yet and now scared to install it because it will cause problem . I get really sick and tired of that stupid check engine light codes and last attempt , will clean the maf . i hope that can solve it