Replacing sidelamps (5W5) with led works but cause fault serv

I replaced first the front sidelights with led and rear sidelights (license plate lights). That worked well be it that there was an after glow after switching off the lights. But the fault error keeps showing up. What causes the ecu to give a fault: complete resistance (burned out light) or does it use a resistance (ohm) criterion? Obviously the resistance of the led is lower then the normal 5W5 . How solve this? In some countries the old 5w5 are unavailable. Must one change the parameters in the ecu ? is that possible?