Okay guys, I was driving home tonight cruising along the farmer freeway, all of a sudden the cruise control disengaged, the check engine light came on, and the cruise control light started flashing. Does anyone know why this might be? It used to come on before I got it tuned when the boost would spike. But I was just driving sedately this time. Does the cruise control light flash every time the check engine light comes on, or just when it boost spikes? Any help would be appreciated...

What sort of mods do you have mate and how much boost are you running?

Hmmm by the looks of your avatar you have a 06 impreza, i guess you're also running ecutek?

If so, i would have a check to see if they increased your EGT temp tables as when you run leaner mixtures the EGT's will start to climb higher then they were set to by factory.

It could also be anything else.. so best get the code pulled from the car and then make your judgements.. but from the description given it sounds like a P0420 Cat inefficency CEL.

Mods are tbe, bigger tmic, fuel pump and tek3. I can't remember exactly, but I'm sure I'm only running around 14psi.
The light still hasn't gone off. I've taken it for a couple drives just to see if it would go off, because when it would come on before from boost spiking, it would turn off again. I'm planning on taking it to race torque wednesday morning, as I have plans to drive down south on wednesday, but I'm not keen if the CEL is still on. Does anyone know if they will be open???

Mmmmm 14psi is about the limit of a TD04 on a 2.5....any more than this and you will be blowing hot air and well outside the efficiancy of the stock turbo....I wouldn't have thought that 14psi would cause boost cut resulting in a CEL....have you got a boost gauge to check?

Na, don't have a boost gauge. But I don't think it was from a boost cut this time. That's what used to happen before I got it tuned...