I've had continual problems with this exhaust light coming on (and staying on) and been told various reasons why its happening. Been into the dealers on no less than 8 occassions with this. They've reset it a few times, changed the cooling fan, changed some unit that was at 'fault', told me I was overfilling the tank, putting the wrong kind of juice in it and it just kept comming back on. The most recent solution has been to remap the ECU and after a week it hasnt returned so far.
I'd get a second opinion if I were you Cat.