Radio interference when rear defogges switch on

mikes5 · May 18, 2017

I have radio inteference when rear window defogges switch is pressed and on.

Any advice would be appreciated

Thanks Mike

TigerFish · May 18, 2017

The antenna is built into the rear screen. Probably worth checking for any scratches or bad connections and/or earths on the element causing a bad circuit.

is200 Newbie · May 18, 2017

This may sound like a daft thing to check against something that seems to point to the rear antenna but I had interference on the radio stations a while back even in areas where I knew there was a strong signal.

Not long after that I needed to replace the car Battery as it started to fail and once the Battery was replaced the interference went away. I didn't do any other work but I did disconnect the heat sensor on the Battery box and re-connect it when the Battery was fitted.

You might want to try two things that wont cost you anything

1. Disconnect the sensor, clean and re-connect it.

2. Disconnect the Battery, both terminals, leave for an hour or so, re-connect and then try the radio stations. You will need to reset the windows etc

This worked for me but maybe by chance more than anything?

jumbojake · May 18, 2017

I had this with my old diesel avensis.

Agree it sounds like it could be interference from the rear window .. radiating from a 'noisy' current accross the heating wires and picked up by the arial at the top.

Could be the alternator, maybe early sign of the rectifier starting to breakdown..... worth trying with the engine off, so you have clean DC current out of the Battery.

chr15gb · May 19, 2017

You are not alone, I lose FM reception completely when I switch the rear demister on.

The rear elements don't seem to form a complete loop (on mine), there are loads of dead ends and gaps. I don't mean small gaps, a good couple of inches. It looks like it is designed like that.

I have read there is an Amp above the rear roof liner but I haven't had the guts to start pulling anything out to find it.

Heat Sensor on the Battery box sounds interesting, I haven't noticed that.

JamieG4454 · May 21, 2017

I've had this problem from years, even worse now I have a dash cam wire going around my windscreen its like it has weakened the signal even with de-mister off.