this is possible upgrade yes, but please ensure your Eberspacher Airtronic D4S is the later generation H Kit compliant version (The H Kit logo should be visible on a side margin of the heater dataplate - see image attached) If you are unsure, please email a photo of your heater dataplate to sales@butlertechnik.com
If your heater is H Kit compatible then please review electric circuit diagram - also attached
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