SZR at speed is the worst place for something like this to happen, ngl. Respect for pulling over calmly instead of panicking. One thing I'd add for anyone reading this thread later — if the message comes back a second or third time, don't just restart-and-drive again. Get it scanned even if it clears itself, because shadow codes really do disappear on their own after enough drive cycles and then you're diagnosing blind.