Piston Slap: To Flash or Not To Flash Your CHMSL?

Sajeev Mehta
by Sajeev Mehta
piston slap to flash or not to flash your chmsl

Chris writes:

I’ve noticed various new-ish cars, ranging from Kias to Lincolns, with a flash-then-steady mode on their center high-mount stop lights. Is this becoming standard? I expect it’s not federally mandated, but I can’t imagine where else it’s coming from.

More importantly, how is it being implemented? I’m thinking about grabbing one from a salvage yard in a few years.

Sajeev answers:

Yes, they’re legal not illegal, but no, they ain’t factory. Mercedes tried to bring them to the US — and failed. You can buy the kit for cheap or, more shockingly, as a (high-margin?) add-on sold inside a dealership’s F&I department. I suspect you are seeing the latter in your neck of the woods, as I doubt people would install ’em otherwise.

I first saw a flashing CHMSL on a C5 Corvette at an open track event at MSR Houston. Thank goodness I was the fastest guy in the novice run, so I could pass the obnoxiousness in my trusty 1988 Cougar. That said, I installed sequential signal lights (homage to the original 1967 model) during its mild restoration in the last two years.

So who am I to judge poor subjective taste?

(Sorry again for not turning my potato sideways. I’ve learned much since 2014.)

I reckon these are a box of solid state electronics, much like the sequential kits on the market today. The three wires splice into the factory harness, but I wouldn’t cannibalize one of these kits if you find one in the junkyard. The data on its safety benefits seems subjective and I doubt it’ll stop an Instagraming driver from rear-ending your ride. More to the point: no amount of flashing is more eye-catching than social media, son!

Look, I don’t necessarily practice what I preach. But if the new Mustangs and even Audi implemented sequential signal lights, perhaps I’ll successfully take the higher ground.

Off to you, Best and Brightest.

[Image: Shutterstock user Bhakpong]

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

Sajeev Mehta
Sajeev Mehta

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  • Ronman Ronman on Oct 24, 2016

    I noticed this yesterday on my soon-to-be father-in-law's GMC Terrain, as well as most city buses and Disney World buses...

  • 415s30 415s30 on Oct 26, 2016

    I have seen a brake light on Evos that blink three times when they hit it. I lift mostly until I need to brake, so in SF when its wet I tap my brakes to flash them to let them know. In my 240Z it's hard to see the small lights, I was thinking of putting an LED tailgate brake light strip on the back of my roll bar so it was really noticeable through the rear hatch glass. I already had someone lightly tap me and my friend's shop did a lot of work for even a small incident.

  • ToolGuy "Mr. President, no government agency, no think tank, and no polling firm knows more about the automobile customer than us. We talk to customers every day. As retail automotive dealerships, we are agnostic as to what we sell. Our business is to provide customers with vehicles that meet the needs of their budgets and lifestyles.”• How many lies can you fit into one paragraph?
  • Spamvw Three on the tree, even Generation X would have a hard time stealing one of those.
  • ToolGuy This trend of cyan wheels needs to end NOW.
  • Kwik_Shift Interesting nugget(s) of EV follies. https://x.com/WallStreetApes/status/1729212326237327708?s=20
  • SaulTigh I've said it before and I'll say it again...if you really cared about the environment you'd be encouraging everyone to drive a standard hybrid. Mature and reliable technology that uses less resources yet can still be conveniently driven cross country and use existing infrastructure.These young people have no concept of how far we've come. Cars were dirty, stinking things when I was a kid. They've never been cleaner. You hardly ever see a car smoking out the tail pipe or smell it running rich these days, even the most clapped out 20 year old POS. Hybrids are even cleaner.