It's not the radio


I have a 2005 Pacifica. When I first purchased it, I noticed that on occassions the radio wouldn’t work. The power was on but there was no reception, not even static. I took it in and they replaced the radio. A week later, on occassions, the AM stations would not receive. Of course, they thought I did not know how to use the radio and was trying to tune in “hard to get” stations. Naturally, when I took it back in, the radio worked perfectly. I suggested that the problem was not the radio but in the antenna or elsewhere. But, they replaced the radio, again. Guess what? The very next day, AM stations were not receiving. I spent a few days observing this behavior from the radio. I noticed that when the vehicle sat in the sun or it was just extremely hot outside that the AM stations would not receive. Again, I returned with the vehicle with this new information. They decided it was the AM/FM modulator located in the roof of the car. So, they replaced it. That seemed to do the trick, for a long while. However, over the last year, when the vehicle sits in the heat, the AM mode will not receive any stations. Reception returns when the outside temperature cools off. Does anyone have a suggestion. Everytime I get an oil change, I tell them my radio problem but nothing is never done because they can’t “duplicate the trouble” and the radio always works at the dealership. Now, I know the response is going to be, “who listens to AM radio anyways?”


“They decided it was the AM/FM modulator located in the roof of the car. So, they replaced it.”

What the heck is that, I wonder? Well, I know what a modulator is, but I can’t think of any reason there should be one in your car. There might be an antenna amplifier in there that, if it went bad, could cause the problem you are having. It sounds to me like it’s gone bad again and it’s a heat related problem. Have you had them leave it out in the sun to try to reproduce the problem? Maybe a hair dryer could heat up the the area of the roof if you know the right location and cause the problem to occur.


I agree with you Ranck. The antenna circuit does sound like it has a RF amplifier in the path. Perhaps the real trouble is the power connection to the amp is intermittent and the amp is really good.

As far as a modulator goes you normally see those circuits in transmitters. Its job is to convert the audio or whatever signal to an electrical signal that modulates the radio carrier signal. The carrier could be AM, FM, or some other signal. The receiver then uses a demodulator to reproduce the original signal.


Where is your antenna located? Is it a “whip”, that is a thin vertical pole located on the fender or is it wires imbedded in a window? I’m curious as to why any part of the system especially a pre-amp would be located in the roof.


Yes, Ranck, we have left it at the dealership sitting in the sun to try and reproduce the scenario-no luck. But good ideas.


WHere are these items located? How does one check for this problem?


Antenna is imbedded in rear side window. Doesn’t it make sense that heat build up in the roof is causing parts located in that area to react to the heat. However, if as you say, there should be no part of the system located in the roof, then where is the fault? And why is it triggered by heat?


The problem would be at a connection. Heating up makes the metal expand and could cause the connection to become loose or short to the ground plane. The wire probably runs through the roof, but I don’t think there are any electronics up there with the possible exception of a loading coil.

AM would be affected greater by a defective loading coil because the AM is a much longer wavelength and it is vertically polarized. When your AM doesn’t work, does the FM work?