First of all, you cannot "disable" the "check engine system" on an OBD II system - it's integral to how the computer works. What was likely done is that the Check Engine light on the dash was disabled (ie, bulb removed) or something similar. Plug a diagnostic tool into the OBD II port and I guarantee you'll get a data stream out.
Of course, the first problem will be all the codes pertaining to the cats being gone...
Given how little restriction modern cats add, I continue to struggle with why people waste the time and money to do this.
Work through the codes and figure out what is going on.