# Strobing center brake light, noise from BCM



## McNeo (Dec 17, 2013)

This may take a second to describe so bear with me...

I bought the following item and installed it on my center brake light (I actually have it installed in the brake light housing itself):

Brake Light Strobe Module | Strobe Modules & Bulbs | Car Bulb Installation Supplies | LED Car Bulbs | Super Bright LEDs

When I tested it everything worked as expected - connect power, strobes for 2 seconds, then solid on. And, when I re-connect it to the car, it works as expected.

What's odd, is now I get noise from the BCM. I know from another thread that the BCM is what controls the center brake light.

When I step on the brakes I get a "THUNK". Almost sounds like a relay, but much more... thunky.

So when I press the brake, "THUNK". When I release the brake, "THUNK". There's only one thunk, it's doesn't strobe-thunk in time with the strobing of the light.

To add to the oddity, this only happens in park. There's no thunk when in gear, and the light still strobes all the same.

Any idea what could be causing this?

Am I damaging my BCM? Or something else?

Thanks.


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## HoPo99 (Oct 31, 2013)

I'll get you the schematic... But it's not going to give an answer. They don't like to show the innards


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## cruzester (Apr 26, 2011)

Your instructions do state it TWICE - _Used with LED brake & reverse lights only_. Make sure you use an LED bulb and then Bob's your uncle...


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## HoPo99 (Oct 31, 2013)

Ok so as an EE here's my take on this diagram.

you can see the "switch" for the center light. If I were designing the circuit I would drive that light with a MOSFET transistor that's controlled by a logic IC. It's cheaper, faster at switching, lasts longer, and is more reliable than a relay. Clearly a relay is not used cause we would hear it every time the brake is pressed

So the click or thunk you hear is coming from something else. It is obviously related to this schematic but it's not part of the violet/white wire line.

beyond that.... It's just a guess of what it is. 

As for hurting it??? These modules are pretty good at detecting destructive circuit behavior and lock out and set a code when they find something bad... So I would guess nothing is getting damaged but it also dosnt sound good.


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## McNeo (Dec 17, 2013)

cruzester said:


> Your instructions do state it TWICE - _Used with LED brake & reverse lights only_. Make sure you use an LED bulb and then Bob's your uncle...


The center taillight is LED stock...


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## McNeo (Dec 17, 2013)

HoPo99 said:


> Ok so as an EE here's my take on this diagram.
> 
> you can see the "switch" for the center light. If I were designing the circuit I would drive that light with a MOSFET transistor that's controlled by a logic IC. It's cheaper, faster at switching, lasts longer, and is more reliable than a relay. Clearly a relay is not used cause we would hear it every time the brake is pressed
> 
> ...


I'm not sure what's in the strobe controlled - I did open it but it's all covered in black silicone.

No codes, MILs, or warnings on the DIC.


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## SneakerFix (Jul 28, 2013)

Sounds like your hearing the safety switch since it only happens in park


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## McNeo (Dec 17, 2013)

SneakerFix said:


> Sounds like your hearing the safety switch since it only happens in park


Hmm, interesting thought.

Based on the schematic nothing else is controlled by this wire except the center brake light. Plus, I litterally have it wired directly to the center brake light (it's soldered to the board and housed inside the center brake light itself.

Again, I'm not sure what's in the actual strobe unit. I wonder if it's giving some sort of feedback through the hot line and in turn affecting other things.

I can tell you at least that it's not affecting the side brake lights, those come on steady right away.


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## HoPo99 (Oct 31, 2013)

Ok I found a problem 

based on our chat last night, you wired this up exactly how figure 3 says not to. You need to cut the violet/white wire and run in series with it


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## McNeo (Dec 17, 2013)

HoPo99 said:


> Ok I found a problem
> 
> based on our chat last night, you wired this up exactly how figure 3 says not to. You need to cut the violet/white wire and run in series with it


It's wired correctly.

Inside the center brake light housing it switches to a white and black wire. White hot and black ground.

I desoldered the white wire from the circuit board of the brake light and attached the blue wire from the strobe unit there. I then spliced the white and brown wire together.


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## HoPo99 (Oct 31, 2013)

Ok back to square 1


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## SneakerFix (Jul 28, 2013)

Can you have someone push the brakes while you check the control unit of the flasher and the neutral safety switch for the sound


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## McNeo (Dec 17, 2013)

SneakerFix said:


> Can you have someone push the brakes while you check the control unit of the flasher and the neutral safety switch for the sound


It's definitely coming from the console, not the strobe unit.

Where is the neutral safety switch? If it's near the BCM might be hard to distinguish the source.


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## McNeo (Dec 17, 2013)

Well...

My buddy came over and I gave him the whole run down about what's going on. We went outside to take a look, I hop in the drivers seat and say "okay listen," hit the brakes, and... Nothing.

No more thunk and everything works including the strobing.

Maybe the car just needed a few cycles?

Frickin weird. Frickin computers.

So, I think I'm all good?

lol thanks guys.


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## HoPo99 (Oct 31, 2013)

Dang how late do you guys stay up up there in Minnesota eh?


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## McNeo (Dec 17, 2013)

HoPo99 said:


> Dang how late do you guys stay up up there in Minnesota eh?


lol I've already put in over 36 hours this week so I'm only working a half day today, going into the office around noonish.


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## SneakerFix (Jul 28, 2013)

It's in the center console


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## McNeo (Dec 17, 2013)

Well, I thought it was fixed, but it's thunking again.

Fortunately, I found the source!

It's the electronic park assist.

I assume there's a solenoid that pushes out in the center console that locks the shifter, assumingly near the little hole to manually release it.

I removed the brake light for tested and it still thunked even with the brake light removed.

I know the change in the brake light couldn't have made the park assist start making noise, so I started scratching my head.

Then I realized that - while trying to find a place to wire the strobe unit - I had the side panel off the center console looking at the BCM. When I put that panel back on it took a few love taps to get it to seat right again.

SO...

I'm guessing my love taps wiggled the park assist solenoid.

Assuming that's the case, is there anything to worry about?


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## obermd (Mar 3, 2012)

Pull the panel off and reseat the parking assist selenoid. It's probably just loose but it will drive you nuts if you don't fix it. Thunks and rattles are ...


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## SneakerFix (Jul 28, 2013)

Mine makes the same sound when in park


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