Catalytic Convertor Lifespan

Is there a specific length of time or mileage that a cat will last?

My 2000 GTP has 149,000 mi on it and still has the original OEM catalytic convertor installed.

How will I know if it is or is not working correctly.

There are no problems with how the car runs but it has crossed my mind from time to time that it should be wearing out or clogging up or something.

I am taking it in to get the U-bend deleted this weekend, should I have them replace the cat at that time?

They are designed to last the lifetime of the car. However, it varies as to when one will fail. Too many variables and we would be speculating. I've seen CATs fail as early as 30K miles and last to well over 200K miles. The GM basic CAT warranty for 97 - 03 model GPs is 80K miles/8 years, whichever comes first. Certain 2001 - 2002 models were delivered with bad CATs from the factory but GM increased the warranty to 120K miles/10 years.

If you are not having problems even with your mileage your CAT is probably fine. Normally when they degrade a DTC of P0420 (convertor efficiency) will set and trigger a SES light. Also, a bad CAT can cause misfires.

The GM dealers and muffler shops can test CAT efficiency and exhaust backpressure to determine if a CAT needs replacement. In your case since you have a GTP you'd be better off getting an aftermarket hi-flow CAT at the same time you do the u-bend delete.