The ICOM propane conversion does not splice into the factory wiring harness or fuel system at all, and will not cause any warning lights to come on. The only wiring into the vehicle is to the battery and 1 wire to a spark plug for RPM monitoring.   Since holes must be drilled into the intake manifold for injector placement, (for a bi-fuel conversion) reversing a conversion may require installing a new intake manifold or plugging these holes in some other way.   A properly installed and tuned conversion should, in most cases, not cause any trouble for a vehicle’s onboard diagnostic systems or ECM/ECU.