The AHM (trailer module) should not need coding on any E53s, to my knowledge. (This is a great example of why we don't use ChatGPT to diagnose car problems, if we didn't already know that...)


If you get the check lights message as soon as you turn the car on with the AHM plugged in, it sounds like the AHM is shorting something out that is not shorted out when it is disconnected. That makes me think it's an issue with the AHM or the AHM wiring. But the car reverse lights come from the LCM if I recall correctly, so that seems odd that the LCM would stop illuminating the reverse lights when the AHM is connected. It makes me think something is shorted (or perhaps was shorted and now is broken) due to the original shorting and melting issue. Someone else might chime in here as I am not an expert on the LCM other.


You might consider just using some splice connectors to splice into the tail lights, and wiring up your trailer module that way. You'll get the "check lights" message but at least everything will work. My car was wired up this way when I bought it and I towed for four or five seasons with it like that, before I spent a bunch of money on a wiring harness and AHM module.

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2003 3.0 5MT Topasblau
Purchased in 2016 and sold in 2024
2012 35d Platingrau