Toyota Repair: P0420 Code, p0420 code, battery cables

Question
Mike-
We have a 2001 Sienna van with just over 88,000 miles on it.  Back in January, we had the O2 sensor in the convertor replaced.  Then in May the friendly check engine light came back on.  This time we had to replace the convertor (Meineke).  Well this past week the check engine light came on again.  Since I was out of town, my wife took the car to Auto Zone and code P0420 came up, which of course means catalytic convertor trouble.  The vehicle has been running fine, no loss of power or anything like that.  Since the van is running fine my brother in law suggested clearing the code by disconneting the battery cables and see if the check engine light comes back on.  Well since the Sienna is staring to dollar us and we don't have tons of money (one kid in college and the other going next year), I decided to take his advice.  The check engine light has not come on in three days since disconnecting the battery.  My questions to you are if there is a problem (with my luck I am sure there is) will the check engine light come back on?  Also by doing what I did, could it cause further damage to our vechile?  Sorry to have rambled on and on.
Thanks for your help,
Ron  

Answer
Wont hurt anything to disconnect or reconnect the battery.
Just do it with the key out.
Autozone can clear the code also.

If theres a problem, the light wiill return.
More specifically, the code is Cat Converter efficiency.
The ECU sees the same reading from the sensor before and after the CAT. So the Cat is not working.

There should be some warranty on the Cat, no?
If P0420 returns, off to Meineke you go.

Mike