Originally Posted by gaedikus
idk guys, IAG explained my CEL code was a result of a catless DP on an 04 STI without a proper tune. the car was rejecting cruise control and eventually threw a CEL/"Cruise" light blink at me. they explained that this was caused by a difference in backpressure that the car wasnt tuned for.
i doubt IAG lied to me to get extra $$, but theres always that possibility. anyway, after i swapped back to an OEM DP the code was cleared and there hasnt been a problem since.
There is no such DTC's for back pressure. The codes you had were likely due to the lack of the catalytic converter. It should have a stored code of P0420 catalyst efficiency below threshhold. IAG knows there stuff and I know just as much. Maybe you misunderstood what they were trying to explain?