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I have the same issue.. it's the amp in the headliner.. mine will work so so and then if the car is turned off the next time you get in it may or may not work until it's restarted again.. so I figure it's the amp.. haven't checked into replacing it, but I will have to shortly..
 

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Unfortunately, it's more than just an amp. There are multiple antennas involved here: AM/FM/TV. The unit in the headliner is the control module for selecting the correct antenna for what you need it for plus it handles the diversity switching for FM. The COMAND unit sends a logic signal to tell the antenna unit which band, it then receives the signal from the antenna unit, demodulates/etc, and then sends that demodulated signal back to the antenna unit and it determines if it needs to swap to a different FM antenna.

So, you might want to make sure that all the RF connectors on the back of the COMAND unit are seated. Unfortunately, the headliner is in the way of the antenna unit itself so you can only hope it's OK.

Another thing you can do is press on the edge of the headliner against the rear window. The antenna unit contacts the antennas on the rear window via springs. If the reception gets better than it is the springs which are no longer contacting the antenna array in the rear window.

I have attached a pic of how I hid an FM dipole antenna in my dads 2001 S500:

 

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Discussion Starter #4
Unfortunately, it's more than just an amp. There are multiple antennas involved here: AM/FM/TV. The unit in the headliner is the control module for selecting the correct antenna for what you need it for plus it handles the diversity switching for FM. The COMAND unit sends a logic signal to tell the antenna unit which band, it then receives the signal from the antenna unit, demodulates/etc, and then sends that demodulated signal back to the antenna unit and it determines if it needs to swap to a different FM antenna.

So, you might want to make sure that all the RF connectors on the back of the COMAND unit are seated. Unfortunately, the headliner is in the way of the antenna unit itself so you can only hope it's OK.

Another thing you can do is press on the edge of the headliner against the rear window. The antenna unit contacts the antennas on the rear window via springs. If the reception gets better than it is the springs which are no longer contacting the antenna array in the rear window.

I have attached a pic of how I hid an FM dipole antenna in my dads 2001 S500:

thanks for the response , I took the command out this weekend and all the connections where good from that end. I looked in the trunk and those connections above battery seemed ok. I tried to push on the headliner to see if I could get better reception , it didn't seem to matter.

I am seriously considering just running another antenna , but I am unsure of how I will route the cables from behind the dash. I have heard good things about the Blaupunkt Autofun windshield antenna and figured it would be the easiest to run behind the dash up the pillar to pass top windshield.

I would love to see how you ran that antenna on your dads or thoughts , how did it work out for you?

I still am contemplating replacing the amp in the headliner , it just seems like a bigger job and higher cost than running an aftermarket antenna.

Thanks!
 

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Any wires I run behind dash from rear of car go under drivers side carpet, up behind center console and in the corner where dash and console meet.. works great and you don't see a thing..
 

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I used the RF cable from the OEM GPS, put on the motorola style RF connectors, an AM/FM amp that comes on when the car is turned to ACC, and then the dipole antenna hidden in the bumper.

Obviously, you will want to use your own RF cable and not the factory GPS cable like I did as you will loose GPS functionality. I had just installed a new aftermarket head unit so I no longer needed the old GPS to be functional.

But, cmpcpro basically outlined how to do it. Another way, would be to reuse the CTEL cable. I had thought about this originally. The cradle in the arm rest sports an RF cable, but, I don't know if this cable leads to the CTEL/TeleAid system under the passenger seat, or, if it goes straight out to the trunk, into the combiner/amplifier, and then out to the antenna in the bumper (FYI: there is a CTEL antenna in the bumper).

There is a distinct possibility that the CTEL antenna from the center armrest could be used. As the combiner/amplifier has two inputs: 900-1800MHz, and E911. I assume the E911 is the TeleAid system under the passenger seat and the 900-1800MHz is the CTEL. But, this is just me thinking out loud.

I'd just run a cable like CMPCPRO says, then mount that antenna somewhere. Maybe like a XM antenna in the middle of the rear trunk lid.
 
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