Doc Tadek

Repost from Tech Section due to advice from other members - admins, please don’t kill me!

Hello all,

I have a 2004 E55 AMG that starts developing some electrical gremlins. The car sits in an underground garage and as it is not being used daily, therefore I have a main switch installed to separate the battery from the cars electric circuit to avoid battery drain.
Now some of the symptoms:
All of a sudden, the tire pressure monitoring system stopped working. As it stopped working for all four wheels, I‘d assume it is not a sensor failure, as I consider it very unlikely that all sensors stop working at the same time. Is this assumption reasonable?
This season after I reinstalled the battery (i had it removed over winter for charging), the key fobs would not unlock or lock the car. Sometimes they lock and unlock via IR, but they do not work through the radio transmitter at all.
I do not assume that the car can „forget“ the key fob sync just because the battery was removed for a few month?! Can someone confirm?
I understand the radio signal amplifier module is not only for the radio, but also for the key fobs. Is it also responsible for communication with the tire pressure sensors?
I read lots of info about faulty / corroded wiring for the radio amplifier module, but this was all related to the S211 wagons, not W211 sedans. I checked my wiring in the trunk and it all looks like new, however I have to admit that I have no idea where exactly the radio signal amplifier module sits in the W211 sedan. Can someone give me a hint.
Any ideas what diagnostics I may run or what to check to figure out what is causing the issues with the key fobs?

Best regards,

Tadek

cetialpha5

I'm assuming you did the basics of changing the batteries in the keyfob correct? Also did you use fresh batteries and check them with a voltmeter? Lots of new batteries sitting on the counter at various stores have been there a while and can be dead out of the box.

As for TPMS, did you scan the car for error codes? There are many cheap scanners out there that can scan for MB specific codes and are under $100.

Doc Tadek

Yes, checked batteries with voltmeter, all well above 3V. Tried both key fobs. Same symptoms.

I have two scanners which seem to only read engine OBD / emissions relevant stuff, but no other functions.

I would buy SD if there was a trustable source at acceptable price (in Europe), but I have no time or patience to mess around with some Chinese copies.
it is like with the WIS that I got for all Daimler/ Mercedes cars, but that only runs on some kind of virtual environment. I got it years ago, every time I want to use it, you have to mess around with something to get it running, it is not easily possible to export or print anything - completely useless! I absolutely hate it!

Doc Tadek

I read that on the wagons the wiring is usually corroded in the trunk (there seems to be a crimp connection where the corrosion starts). On sedans there seems to be an issue with wires breaking due to the flex in the complete wiring loom when opening the trunk.

Can someone confirm where the radio signal amplifier module sits in the W211 sedan? Does not seem to be on the driver side of the trunk with all the other modules. Is it hidden in the C pillar? I would consider it weird if it was in the trunk lid, therefore not sure how cables going to lid would affect that.

konigstiger

Rear left c-pillar.

jasontCAN

I had the same problem after a battery change when my alternator went kaput.

If your problem is like mine, your car alarm siren is shorted.

Try and set off your car alarm. If the lights go off but there is no sound, you'll have a pretty good indication of that being the problem.

I don't care about the siren so I just unplugged it and waterproofed the connector such that it wouldn't short again. My locks work now.

Cheers

Doc Tadek

Thanks a lot for this advice!

Indeed, the siren has never ever worked since I bought the car. I have no idea whether it is broken, unplugged, or just turned off via SD. But I can check the connections.
Where is the siren located? On my Volvo both horns are infront of the radiator and the third one for anti theft alarm is on the bulkhead of the engine compartment. Not sure I have ever seen another siren or horn in the engine compartment of the E55.

konigstiger

Check f8 @ rear SAM (trunk), attachments support siren replacement if need be.

jasontCAN

The siren is behind the wheel liner on the drivers side front wheel. Konigstiger sent a video that shows where it is/how to remove it.

If you don't care about the siren sound working, don't bother with buying a new one. I just unplugged and removed my broken one and the remote locks worked. Just make sure to cap off the connecter that used to be plugged in so water doesn't short it/so it doesn't corrode.

Once you remove the siren, replace fuse #8 in the trunk (the 8th fuse from the bottom). It's supposed to be a 7.5amp fuse.

Before putting in the fender liner/reassembling, test if the locks work. Hopefully they do.

For me the fix costed about $0.05, just the cost of a new fuse.

Let me know if anything is confusing.