This is how I reproduce the issue:

With the '16 Mazda CX-5 turned On, the shifter in Park, and the radio On, I begin to press the brake slowly. While the brake is slightly pressed but the brake lights are OFF, nothing happens. As soon as the brake light turns on, the radio interference occurs.

I just noticed because I only listen to the radio on long drives through rural areas, so I simply thought that the antenna was just not picking up the signal.

What can it be? It doesn’t happen with the emergency brake.

  • Do you get the same results when not moving and gently pressing the brake pedal, not so much as actuating the brakes as activating the brake lights?
    – fred_dot_u
    Oct 15, 2019 at 1:01
  • Sorry for the delay. I would need to confirm, but even by slightly pressing the pedal, the radio station receives interference.
    – rbhat
    Oct 15, 2019 at 12:53
  • That's pointing to the brake light circuit, but another test: with the key in acc position, radio on, does brake pressing lightly duplicate the problem? This portion possibly would exclude the brake pressure circuit and focus on the brake light circuit.
    – fred_dot_u
    Oct 15, 2019 at 13:00
  • Thanks for the suggestion. Just checked, and it only happens when the brake light turns on.
    – rbhat
    Oct 16, 2019 at 0:24
  • Does the interference occur on just AM or FM or both? Are your brake lights LED type?
    – Old_Fossil
    Apr 25, 2020 at 9:49

1 Answer 1


The most common cause of radio interference is arcing. This may be a bad bulb or bad wiring or a bad connector/connection. Rear defrost grids are notorious for this.

Unfortunately, this will be a long a drawn out diagnosis. This involves a process of elimination to see where the arcing is located. First, look for any lights that seem dimmer than the others. If you find one, pull out the bulb and see if the problem goes away. If this doesn't do it then remove one bulb at a time until it goes away. Look for burnt or belted contacts. This process continues until a bad/arcing connection is found.

  • Thanks for the reply and sorry for the delay. I checked, but didn't find anything, so I took it to Mazda. They told me the antenna was the problem and that a new antenna would fix the issue. Does that make sense?
    – rbhat
    Oct 25, 2019 at 19:34
  • @rbhat To me, it does not really make sense.
    – vini_i
    Oct 25, 2019 at 19:38

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .