ive searched but havent found a definate answer.
ive been told that you can use a jumper wire on two of the pins on where a chip would go on a chipped ecu and you can run the ecu as if it were never chipped or "stock" again.

The ecu i have and would like to do this to if at all possible is a P28

 

You would remove/cut the jumper at j1 on the ecu.
For more information read http://www.phearable.net/tech

 

thanks