Radio static after installing new brakes

Tiny
JERRY DURO
  • MEMBER
  • 2003 CADILLAC CTS
  • V6
  • RWD
  • AUTOMATIC
  • 62,000 MILES
I have been installing brakes ever since I held a wrench in my hands. After I installed the new brakes I noticed that every time I depressed the brake pedal I get a lot of static on my AM channels. This has got me stumped.
Jerry Duro
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Sunday, December 4th, 2016 AT 7:21 PM

13 Replies

Tiny
CARADIODOC
  • EXPERT
AM radio picks up "radio frequency interference", (RFI) which means anything that causes voltage spikes, like lightning. In this case you've already identified how you can make the noise occur, but we need additional observations to narrow down the cause. Does the noise occur only when the engine is running or any time the ignition switch is on?

If the engine must be running, the generator is a common source of harmful voltage spikes on GM cars beginning with 1987 models. To verify that, unplug its small connector at the rear / side, then run the engine. If the noise is gone, suspect the generator has a failed diode. That is caused by those voltage spikes it develops. To reduce the high number of repeat generator failures, always replace the battery at the same time, unless it is less than about two years old. The battery is the key component in absorbing and damping those voltage spikes. They lose their ability to do that as they age and the lead flakes off the plates.

Also consider the anti-lock brake hydraulic controller. You may want to temporarily remove the two fuses for the ABS system. If the noise stops, look for a rusted / cut / forgotten ground strap between the body and engine, body to hood, etc.

Observe what the noise sounds like. A generator produces a high-pitched whine that increases in pitch as engine speed increases. Ignition system noise is lower-pitched, and tends to get louder when engine speed goes up. Static that sounds like a weak station, but it changes when the car isn't moving can be caused by antenna problems. GM refused for many years to give up on the disaster that put the antenna in the windshield or rear window. Those tiny wires break from vibration and extreme temperature changes. If you have the more reliable antenna in the front fender, wiggle the base to see if the noise changes. If it does, its ground might not be making good contact with the sheet metal. If yo have a power antenna, those have a ground strap attached to the base. Be sure that isn't corroded off.

If the noise definitely just started after the brake service, the suspension was allowed to extend fully when the front end was raised off the ground. Often there will be ground straps attached to the struts' upper mounting plates, or between the lower spring plate and the lower control arm. Check if one of those was just about corroded through, and extending the suspension was the final blow that broke it.
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Monday, December 5th, 2016 AT 3:36 PM
Tiny
JERRY DURO
  • MEMBER
Thanks for the fast reply. You gave me great leads as to the problem. I'm working on the car tomorrow and I'll check them out.
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Monday, December 5th, 2016 AT 4:06 PM
Tiny
JERRY DURO
  • MEMBER
Static is still there after ignition is turned off. It keeps the radio on for about 30 seconds. I hit the brakes within those 30 seconds and I still get AM static. I've looked all over for the ground straps so far I can't find them. With the engine off I suspect that that might be the problem.
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Tuesday, December 6th, 2016 AT 1:51 PM
Tiny
CARADIODOC
  • EXPERT
Did you try unplugging the brake light switch? Remember there's going to be a circuit in it for the cruise control. Also, most cars since the mid '90s have at least one computer that doesn't go to "sleep" mode for up to 20 minutes, so what you think is turned off might not be.

Try unplugging the rear lamp assemblies. If the noise stops, inspect the bulbs and sockets for corrosion or signs of arcing.
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Wednesday, December 7th, 2016 AT 7:14 PM
Tiny
JERRY DURO
  • MEMBER
I used your advice and I found the problem. Cadillac 2003 red trunk light. I unplugged it and the static stopped. Before I take it apart does anyone have any experience with the center stop light?
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Tuesday, December 13th, 2016 AT 10:54 AM
Tiny
STEVE W.
  • EXPERT
I would suggest that you have a bad ground connection to the light or inside the light on the circuit board. Possibly due to moisture entry corroding the traces on the board.
The ground for the light is next to the left rear shock tower. If you want to test it without pulling trim you could bare a small section of the Black wire and run a jumper to a good ground. If the noise goes away you would need to dig out that ground and clean it. It is also possible that the power feed to it is the issue. The test ground should show that as well.
If the test ground is good but you still have the static then look for a splice that is under the carpet next to the drivers side seat rail. It is the splice that powers the rear lights. It will have three light blue with white stripe wires and one solid white. The white is the CHMSL light, two of the LT BLU/WH wires go to the rear lights the third is the power from the brake light switch.
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Tuesday, December 13th, 2016 AT 2:11 PM
Tiny
JERRY DURO
  • MEMBER
Checked the grounding and its perfect. Doubled checked all the way to the brake switch. I then pulled the trim and checked all the way to the tail light connection. No ground problems.
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Tuesday, December 13th, 2016 AT 4:09 PM
Tiny
STEVE W.
  • EXPERT
Well good news but not so good. Usually static is due to a poor ground on an electronic item. The only other ground I can think of that could allow noise would be the antenna ground and the stereos ground. But if the radio works and you don't get static on any function but AM. The issue is in the lamp itself, it shouldn't generate any RF that can escape it but something like a failed capacitor or bad driver circuit is allowing the RF to follow the power lead into the electronics. The only other test I can think of would be connecting the lamp to a different power source and place it near the antenna and see if the static is still there. You might be able to install a noise filter in the line but that may not help if it is also radiating the signal.
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Wednesday, December 14th, 2016 AT 10:55 AM
Tiny
CARADIODOC
  • EXPERT
Thanks for the info. Steve W.

As a point of interest, I doubt this is a radio problem. The reason this is only heard on AM is that signal is "amplitude modulated", meaning the audio signal changes the amplitude of the main radio signal. The changes in amplitude are what is detected as the audio signal. Anything else that resembles a similar change will be picked up and heard in the speakers. Most commonly that is the voltage spikes from the ignition system, and from lightning. You'll never hear lightning on an FM station. That is frequency modulation. The audio signal causes slight variations in the main signal's frequency. The radio's circuitry chops off the top and bottom of the signal, so any voltage spikes from interference are also chopped off.

I know that wondrous story doesn't help solve the problem, but it should steer you away from suspecting a radio problem.
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Wednesday, December 14th, 2016 AT 1:57 PM
Tiny
STEVE W.
  • EXPERT
CARADIODOC I doubt it's the radio itself but if the antenna or chassis had a bad ground the RF would have an entry point. Seen more than a few issues on ancient mary caused by bad grounds or poor shielding.
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Thursday, December 15th, 2016 AT 9:34 AM
Tiny
JERRY DURO
  • MEMBER
Further checking the tail light is a Neon bulb which has a ballast. I think that is the problem. There is a LED conversion kit I found on the internet.
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Thursday, December 15th, 2016 AT 4:10 PM
Tiny
CARADIODOC
  • EXPERT
Dandy. I suspected some type of circuitry that involved high-frequency switching, but there is nothing like that in standard light assemblies with incandescent bulbs. I never pursued that thought because there isn't anything like that in LED systems either unless it is dimmable, and there's no reason to use dimming lights for brake lights.

My next question is why didn't that cause a problem before you did the brake work?
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Friday, December 16th, 2016 AT 1:02 PM
Tiny
STEVE W.
  • EXPERT
Hmm, Usually they just die, first one I've heard of that generated static but still worked. Then again, many folks don't listen to AM these days so it may be very common and just not discovered. Have to toss that one into the new info box.
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Friday, December 16th, 2016 AT 1:50 PM

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