Couple of plans of attack here- I scale mine inversely (0v = lean/ 22AFR, 5V = rich/ 8AFR) so if the MXTL dies then it'll overfuel rather than run lean. The ECU can be set to work on a narrow range, as most sensors do- 0.5 to 4.5V, either side of that (0 or 5V) will register as a sensor fault- I tried this but kept getting false ECU alarms, I don't think there is a time delay on the alarm so it activated each time the car started. Thirdly when you set up closed loop it is only active under certain conditions, typically cruising/ steady throttle. Furthermore there is trim limit, so it can't or subtract more fuel than that setting- I think I set mine to 8%.
