My friend got a Check engine light the other day in his new 06 si. He went on the highway and opened it up a couple times after gettting new exhaust and intake. They disconnected the battery and it went away, then it came back the next day. Do you think it is the parts or is it from drivig the car hard? I would think that when honda made the car, they were expecting people to drive it hard. The parts installed are DC header, DC cat-back, and AEM intake. Would that cause a check engine light?

 

Probably the o2 sensor, Sounds like he put the race header package on.

 

the o2 sensor is still connected, sometimes the CEL comes on after hitting potholes, if that helps.

 

put a defouler on the 02 sensor and you will not get that problem. You will have a CEL since you have no cat on you header