As with everything Hyundai EV, there is an algorithm for this. Regen does activate the brake lights but only when the braking algorithm detects sufficient deceleration. As a rule of thumb if braking exceeds regen level 2 the brake lights will activate. Of course the algorithm is a bit more complicated then just coming on at regen level 2. It will vary the deceleration required to activate the brake light depending on circumstances, but you can pretty much guarantee regen 2 or greater will turn them on.

 

Do the IONIQ 5 Brake lights come on with different regen levels? - YouTube

 

Thanks for the video link, guess my wife must have had it in a lower regen factor when I was following her home from the dealer.

 

Same on our 2022, I can see the brake light come on when using level 2 or 3 regen without touching the brake pedal.

 

Tesla shows it on the car icon on the screen. Hyundai could easily do the same along with scores of other things that would be easy programming. Don't get me started on the lack of key fob/profile optiosn.

 

I've done a bit of testing using an OBD2 reader and CarScanner to monitor brake light activation, and something I haven't seen mentioned is what happens when using cruise control.

I found that when coming up behind another car, the brake light activates even when the car only has to slow very gently, once the distance setting decides we're getting too close to the car in front. So in an ICE car, you would just lift off the gas a bit, and the car would slow enough so you are no longer gaining on the car in front.

Since the scenario I'm describing feels like very gently (regen) braking, like level 1, I would have assumed, and preferred, that the brake lights not activate. Too me, very gently slowing, just to reduce speed to match the car ahead, and when you are still about 100 feet behind it, shouldn't activate braking. That may seem extreme

The second situation is when you start going down a gentle slope while doing 60 mph (100 kmph). Since the car rolls so easily, it starts picking up a bit of speed, and even at just one or two mph above the set cruise control speed, the (regen) braking activated and the brake light came on. Even though level one regen braking would be more than enough to keep the car at the set cruising speed.

I'd be interested if anyone else confirms this behaviour, which I haven't seen mentioned elsewhere.

 

I think it’s the result of a brain explosion by Hyundai software designers. Although probably borrowed from other EVs.

Your second scenario sounds right. Have seen it in a Leaf, but haven’t had the chance to see it in the Ioniq 5. But that behaviour would make sense to me. I was following a Leaf down a moderate slope and the brake lights were constantly on and off. For varying times on each occasion, from just a flash to several seconds. At first I though it was someone riding the brake pedal but on reflection realised that the regen and slope matched so closely that it was just enough regen to occasionally turn on the brake lights, but not enough to keep them on.

As I said in post #2 above, the algorithm for brake lights coming on is more sophisticated than just reaching regen level 2. My guess is it’s an attempt to minimise rear ended collisions that’s maybe gone a step too far. Whether it’s sensible is another question.

 

The brake light behaviour is a legal requirement for all EVs and the international standard is well documented in these forums.
Deceleration ≤ 0.7 m/s2: The signal shall not be generated
Deceleration between > 0.7 m/s2 and ≤ 1.3 m/s2: The signal may be generated
Deceleration > 1.3 m/s2: The signal shall be generated

 

As I noted based on my "cruise control" (HDA) testing, on my Canadian I5, the brake lights do activate even with a very minor amount of braking force, when using cruise control and picking up speed going down a descent. My testing indicated that the braking force felt much less than level 1 regen, to limit the gradual increase in speed, and the brake lights activated.

In fact the brake lights stayed on, even with no apparent deceleration, to maintain the speed close to the cruise control setting while "rolling" down the descent. Strictly speaking, that shouldn't be necessary, similar to using engine braking instead of physical brakes to limit speed when descending a hill in an ICE.

The same occured when gaining on a car ahead of me in my lane.

I'm not sure if there are any variations in how this is implemented in different countries - I haven'tseen other posts referring to cruise control behaviour, just level 1 vs other level behaviour.

I will be redoing this testing to see if the behaviour is the same, regardless of the regen level set, but in my opinion, under cruise control, HDA should override regen level settings, for the purposes of brake light activation.

I would be happy if the brake lights were consistently activated based on the deceleration rates you describe above.
I've written to Hyundai Canada descriing this behaviour, and will be interested if they agree this is a potential issue. I assume that a software "fix" would be doable, to make it consistent with the "non-cruise control" behaviour, where level 1 regen does no braking.

 

Okay, I just got an interesting reply from Hyundai Canada.

They seem to be saying that, due to decisions by the NHTSA, under cruise control, brake lights must come on when closing in on a vehicle, even if the deceleration is very mild, whereas level 1 regen braking, even if it is a stronger deceleration, does not require brake light activation.

They did not touch on the brake lights activating when cruise control is holding speed on a gentle descent, even at braking levels less than level 1 regen.

I do think that this may cause some issues for following drivers, and would love to know if a) other I5 owners have noticed this behaviour, and b) whether other vehicles share the same characteristic.

 

Here is a post I did a while back. As noted, I put a mirror on the back of my car, angled so I that could easily see the brake light behavior. I drove with a lot of different settings and conditions, and convinced myself that I liked the way the brake lights behaved. Note the photos in the post!

Regenerative braking and stop lights

Hello To stop an ICE car I would put my foot on the brake and the car behind would get the rear stop lights turning red I have my regenerative braking set to L3. When I remove my foot off the accelerator, the car slows quite quickly - exactly what I desire However the car behind me gets NO...

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