ABS light stays on until Scooter restart

[JanWi2026]

Hi all,

I have the following issue with my 2012 Downtown 300i ABS. It started randomly about 2 weeks ago.

When starting the scooter, the ABS light stays on and will only go dark when I restart the scooter immediately. This issues occurs on every start.

I had the ABS light coming on before when the alternator failed and subsequently the battery drained slowly. Once the alternator was repaired, the ABS light would go out once the scooter started moving.

So far I cleaned both abs sensors rear and front from metal flakes but no luck resolving the issue. Any suggestions what might cause this issue?

Btw I’m from an engineering background and used to work on classic vespas, so mechanically I’m very savvy but the ABS system is an unknown to me.

Cheers
Jan

[Ruffus]

JanWi2026 welcome here!
ABS-systems through all brands are sensitive to low voltage during crank process. Battery has to be top.

I don't have particular experience with KYMCOs ABS systems, but..
..had lately to work on late models MotoGuzzi and BMWs  (2010 - 2012) whch had similar problems.
Assuming your battery and regulator are new.

Ignition on, start, ABS warning doesn't dissapear.
After days of measuring current, changing fuses, and head scratching, no real progress.

Then I put a small (8AH) LiFe battery parallel to the bikes starter battery and the prob was solved. Obiousely litios higher voltage does the trick.

It seems that, the voltage drop at the Bb battery during starting causes this irregularity.
In cases of this bikes the generators are powerful eough to charge both.
Should be in your DT case too. No fuse between batteries, and I took 4sqmm soft cables to connect.

Its not said that your ECU will accept that, but its worth a try.
Pls give a feedback or Qs.

[JanWi2026]

Hi Rufus,

Thanks for your thoughts. I have to admit that I didn’t change the battery after the alternator died and was swapped.

Now that I think of it, the problem occurred after a temperature drop (heading into winter here in the southern hemisphere) which may indicate a dying battery. AGM Battery’s age is unknown as I bought the bike with the current battery installed a year ago.

I’ll try and put a second battery in parallel to see if this fixes the issue. Fortunately my partner has the same scooter so I can pinch its battery for testing 

[Ruffus]

Excellent battery is a must on ABS vehicles.
Try a setup with jumpercables first.
If it works out, battery swap.