Troubleshooting a 2009 ML550: Why Keyless Remotes Stopped Working After a Wet Rear SAM

A 2009 Mercedes ML550 owner recently faced a frustrating electrical mystery: keyless remotes that suddenly stopped working. After some digging, the culprit appeared to be a wet rear SAM unit. When the owner pulled the module out, they found moisture in the rear taillight area and minor corrosion on the SAM itself.

The corrosion cleaned up nicely, and new gaskets were installed on both tail lights, oddly, only one of the original gaskets was seated incorrectly. But even after the fix, the remotes remained silent.

Using a Snap-On Solus and an AP200 scanner, the owner found three fault codes stored in the rear SAM: 90C4 (no connection or short to the interference suppression element), 91C8 (linked to LED license plate lights), and 9153 (which may not apply to this vehicle). Notably, a Mid City remote start system had been installed four to five months earlier and had worked flawlessly up to this point.

The owner doesn’t suspect the remote start is the issue, but it’s worth noting as a potential variable.

The owner also checked for a leaking alarm battery, but the alarm unit turned out to be just a horn, no battery to worry about. With no other codes or issues from the rear SAM, the big question remains: should the SAM be replaced? Before going that route, it’s worth inspecting the wiring harness for any hidden moisture or damage, especially around the tail light area.

Also, double-check that the new gaskets are sealing properly. If the remotes still don’t respond, a replacement SAM might be the next logical step.