So I spent all of the last couple of weeks searching for an answer to the problem with my keyless entry. Everything I had found was NOT the problem that I had, so I thought I would post this and let everyone know that there is one other thing to look for.

It's the issue where the keyless entry remote will not work from a distance, but will only work when you point it at the IR sensor at the driver door handle. I had tried replacing battery thinking the key was bad, but still no luck.

I searched the forum and elsewhere for a long time looking for an answer to this problem. I managed to (or thought I did) narrow it down to the antenna amplifier located right above the rear windshield of the vehicle, so I started from there.

The fuse for the RF antenna is in the fuse box in the trunk, #8, 7.5A fuse. I checked the fuse and it was blown. I bought a new fuse and replaced it, tried the keyless entry, and no luck. Gave up for the day.

Couple of days later, decided to actually start looking at the antenna amp and the wiring and figure out what the issue was. I noticed that the new fuse I had put in had blown, very strange. Then it gets a little interesting.

I replaced the blown fuse, clicked the keyless entry button once and it WORKED. Then after that it stopped working, so I checked the fuse and it had blown. So the problem is there was a short somewhere within the circuit.

The fuse #8 controls three things: RF antenna, car alarm, and the convenience locking system. I took apart the whole liner in the trunk to expose the back of the fuse box and all of the wiring coming out of it. I also took apart both of the rear C-pillars to expose that wiring and part of the antenna amplifier. I spent hours tracing the individual wires from the antenna amplifier back to the fuse box looking for any issues with it and could not find anything.

At this point, putting another fuse into the fuse box would immediately blow as soon as it made contact with the terminals (WTF??). That's when I looked at the fuse box diagram and found it controlled the 3 items I mentioned above.

At the back of the fuse box where the wiring harnesses plug in, there are two for the fuse #8. One of the harnesses traces back to the antenna amplifier. The other harness contains two groups of wires run together into one harness. One of them runs to a small black box located right on top of the fuse box. I looked up the part number and what do you know, it's the car alarm module. The other group of wires runs over the passenger rear wheel well, then goes underneath the seat, presumably somewhere towards the front of the car. I determined this is probably the convenience locking module, wherever that may be.

So then using process of elimination, I unplugged the alarm module, as in the other end of the harness that plugs into the fuse box, so only the convenience locking and antenna amplifier were connected to the fuse box. I put in a fuse and it blew, which meant it was not the alarm module that was the problem.

I plugged the alarm back in and then entirely removed the harness from the back of the fuse box that ran to the convenience locking and alarm. Now ONLY the antenna amplifier was connected to the fuse box. I put in another fuse, and then, BAM, the keyless entry worked!! I tried locking and unlocking at least 10 times to make sure it worked and it did. So the conclusion was that the problem is in fact NOT the antenna amplifier, but rather there is a short somewhere in the convenience locking module.

So I have absolutely no idea where the convenience locking module is, nor could I even find a part number or anything after searching online, so I determined: I don't really care about the convenience locking, and I don't really think someone will break into my car, and even if they did 1) there's nothing it, and 2) if they're trying to steal something they're not going to give a s*** if an alarm is going off, they're gonna grab it and run anyway. So I left it unplugged so the keyless entry works.

Now I am trying to figure out where the hell this convenience locking module is so I can actually SOLVE the problem. If anyone knows this information, that would be great.

I hope this information helps some people out. I know that when I was searching to buy a new antenna amplifier online, they are definitely not cheap, and it really would have made me mad if I got one and it wasn't the problem. I've got a temporary solution for now until I figure the rest out.

 

Convenience locking?

Sounds like it could be the function that controls locking the doors at 10mph. I can access this through the dash cluster on my C32, is there an option like so accessible on the C55?

Or possibly when you open one door, and all the other doors unlock?

 

That's what I thought convenience locking was as well, and yes I've got that option. But the weird thing is that even after this temporary fix and the "convenience locking" is unplugged, my car still does that.

The into other thing I've found about convenience locking is that it could be where you can hold down the unlock button on the remote and all the windows will open, and similarly if you hold down the lock button when you're leaving the car all the windows will close so you don't have to worry about rolling them all up when you park the car.

I'm not sure but that's just what I've read.

 

Did a quick search, I think this may be a good read: https://mbworld.org/forums/c-class-w...ock-coupe.html

 

I appreciate the link, will have to look into that. Only difference between my problem and that was the pano-roof on the coupe, but sounds like it could be the same thing.

Thanks!

 

I had the same problem in my c32. As you found out there are 3 circuits on this fuse, My car alarm was shorted. I clipped the wire near the connector on the back of the fuse panel. I don't really need it. If I get really bored I may dig into the circuit, but things break often enough on this car to keep me occupied.

 

Yeah, I dunno if I'm actually going to fix it or not. I don't really care too much about these two things, I'd rather have my keyless entry working. Imagine taking a girl on a date in Benz and you can't unlock the doors unless you go to the driver's side door

If I decide to get busy one weekend I'll post something up

 

Apologies for necroposting but did you ever get to the bottom of this? I too am facing the same issue (fuse #8 keeps blowing). All I really want (for now) is the remote unlock/lock to work for when you are carrying stuff. I am trying to determine where the short is by (carefully) removing the now fragile ABS plastic trim in the trunk lid (is that where the radio antenna amp is?) but some sort of diagram of where these 3 components are & where the wire runs are would be great!

(2002 C230K Coupe (W203))

PS: Is the alarm circuit the anti-tow alarm? If so, can that be disabled via the manual/dash settings to perhaps reduce the current draw VS permanently cutting the wire in the back?

Thanks!