I have an 01 wrx. Had the downpipe replaced last week with a cat bypass (invoice refers to a cobra downpipe, which I have never heard of). Dealer did not do a cel fix. I have done approx 200 miles since, but cel has not lit. Does it take time to register the changes on the ECU or is my cel knackered? Any ideas?
Have to say that the downpipe may be a budget job, but the difference is amazing.

 

it might come on tomarrow, in a few months, or never

If you really want it to trigger a CEL due to cat ineff. drive at a constant speed for awhile. Heavy flogging around town will help keep it off. Either way it doesnt matter if you have a friend with a delta dash to check the code and clear it, harmless CEL anyways.