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

Sajeev Mehta
by Sajeev Mehta

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.

  • SCE to AUX It's fun when liberal interests fight each other.
  • Varezhka Suzuki Jimny, Toyota Century, and I know it technically just ended production but Honda e.
  • CoastieLenn For those that care to read the details of the crash NOT included in this article but published elsewhere- this happened at nearly 10pm when the CRV was stopped in the center lane of travel, lights off, with the driver remaining in the car. Not only is it not known if Blue Cruise was being used, it would have been a nightmare for most alert human drivers to mitigate that driving the 70+mph speed limit on many sections of I-10 in Texas, much less an AV system.
  • Jeff This is what I would want: Toyota has now released an affordable truck called the Toyota IMV 0. The newly developed vehicle made in Thailand comes with a rear-wheel drive and a gasoline 2.0-liter inline-four matched to a 5-speed manual transmission. NEW $10,000 Toyota Pickup Has Ford & GM Crapping ... YouTube · Tech Machine 8 minutes, 46 seconds Dec 26, 2023
  • Jalop1991 At the same time, let's take these drivers off the road--at least the ones that haven't yet taken themselves off the road.I can guarantee, at no point was this guy or any of the dead Tesla-stans actually driving the car. They were staring at their phones, because, HEY, SELF DRIVING!!
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