I understand the potential problems with precats left intact but is it necessary to gut an '02 with only 21k miles, driven only occasionally and not worked hard? What about the check engine light if I gut? I was told by my excellent mechanic not to gut but watch for any loss of power, etc. in case they go bad. Any suggestions? Thanks-
Pre-cat failure is a random event. It isn't related to age or mileage. No one (except maybe Toyota, and they aren't talking) knows what causes the pre-cats to fail. There may be multiple causes.
When I removed the pre-cats from my wife's Spyder, it was nine years old and had over 120,000 miles on it. The pre-cats were perfect.
I have read reports of pre-cats failing at only 23,000 miles.
If the pre-cats fail, the smaller debris particles are sucked into the cylinders and the larger chunks lodge down-stream at the main cat where they plug the exhaust. The plugged exhaust is responsible for the loss of power. The small particles score the cylinder walls beyond repair. If you wait for this to happen, you've waited far too long.