Earlier quoted context omitted.
Engine computers can easily be reprogrammed to make the engine run at all sorts of different operating bands. You could easily detect state emissions equipment, since it must pull information from the ECU. To me- these devices are either pre-programmed operating modes that produce clean emissions but the vehicle would not operate under this tune (emissions testing is often not under load) and so once back on the road…
Manufacturers were doing this well before OBD2. They'd look for a condition where the car was started and then idle raised and held raised, for example. Once things like CANBUS became popular, as well as ECUs getting integrated with ABS/traction control, they'd look for drive wheels spinning and but not undriven wheels. When stability control systems became a thing, they could monitor steering angle and look for the…
I guess the EPAs awards aren’t that great.
I wonder if they also run cars sloppy when it detects something that resembles a drive-cycle for fuel economy testing. e.g. Stop charging battery. Limit A/C or turn on mild heat to reduce radfan load. Limit power steering force. Dim lights 10%. Limit acceleration (gotta be a big one).
Probably enough data out there to identify offenders by comparing real world fuel economy data to official fuel economy.