Modern Vespa

Dear All,

I have a serious issue with my Vespa and I'm looking for advice.

While riding, the engine suddenly cuts off, sometimes starts again by itself, and sometimes stops completely. It can take up to 20 attempts to restart it before it runs properly again. Once restarted, it usually drives smoothly — until the problem happens again.
My mechanic hasn't been able to find the exact cause yet.

Has anyone experienced something similar?

It's a Vespa 300 GTS HPE (2020 model) with 17,000 km.
The issue started recently, right after I changed the front tire and the battery.

Here's what happens when the problem occurs:

The ABS light turns on.

The speedometer goes crazy (drops to 0, then back to the correct speed).

Sometimes the engine warning light appears.

Then the engine stalls — sometimes I can restart it while still rolling, but often I have to stop completely and it takes many tries to restart.

I went to my mechanic, and we connected a diagnostic tool to check the fault codes. The codes showed:

Buffer data full

ABS high voltage / low voltage

We cleared the faults, but the issue immediately came back.

My local mechanic also contacted Vespa, and they suggested it might be related to the injection system.
On my side, I suspect it could be an issue with the ABS sensor. I read that when changing the tire, there's a gap specification between the ABS sensor and the tone wheel that must be respected. However, the mechanic told me he didn't touch the ABS sensor when removing the wheel.

Even if the ABS sensor is at fault, the fact that the engine cuts out and becomes very hard to restart seems to suggest a deeper problem — maybe with the injection system, another sensor, or something else entirely.

It's a very strange issue because the bike drives perfectly for a few minutes, then suddenly has the problem, and then runs smoothly again for 2 to 10 minutes before the issue returns.

Any help or advice would be greatly appreciated!
Let me know if you need any more details.

Thanks a lot in advance.

Possible fuel pump fail. There was a recall for the fuel pump for that year. Get the dealer to lookup your VIN

Thanks for the answer. But how the fuel pump issue may be related to the abs light?

If the fuel pump stops and the engine stops whilst still rolling all your warning lights will come, most telling is your oil pressure light is also on. This condition is as if you are going to start the bike.

The engine may not restart as there is insufficient fuel pressure at the injectors.

Good luck with the fault finding , but check out steelbytes suggestion first .

I admit I didn't read all that you wrote ...

I am stil wondering if you pump is bad ...

... but am also wondering if your new battery is bad.


Note: the speedo gets it's value from the *rear* abs sensor not the front. Also abs problems will not stop the bike running.

This should be moved to General Discussion to get more attention…

Thank you for moving the post.

I understand that the speed sensor/ABS issue may be linked to the rear wheel, as the speed sensor is located there. I have had the Kubler installed for a while without any issues.

Thanks for suggesting the battery issue. How could a new battery cause injection problems?

Noted regarding the injection — so the theory would be that an injection issue could cause a drop in power, which could explain the ABS light. However, I don't understand how this would relate to the speedometer suddenly moving back and forth. Could it be that a faulty sensor is causing all of these problems?

Any opinions or comments from anyone who has experienced similar issues would be greatly appreciated. Thanks!

Hello!!!!

I have a 2022 GTSHPE and am currently at 13,500 miles. There were two times early on (600 miles and again at 5000 miles or so) that my bike acted just like yours.......and for me it was fuel pump, both times. It has been great since the second fix. I would be riding then suddenly it would be like it cut out but at same time all the lights go on........I would stop......and while engine is hot it wouldn't start again, but when cooled down it would......but then would happen again once hot.

A new battery isn't necessarily a 'good' battery. But by itself it's probably not the problem - I'd suspect the connections to it, ensure they're clean and tight.

Did you buy and install it yourself, or let a dealer supply it leave it to a mechanic to install? Dealer batteries, especially sealed lead-acid ones that they added the acid themselves, may have been on a shelf for months while attached to a battery tender. Contrary to popular opinion here on MV, that is NOT a good practice.

Dear members, I have the same problem as in the case of member Vincentbrt. Vespa 300 hpe production 2023 turns on the ABS light as well as the Check engine light. The lights come on after driving a maximum of one kilometer and when I encounter a road with several potholes. The engine starts to lose power and sometimes shuts down. I turn it on without a problem, but it's terribly awkward when I'm in an intersection. The speedometer drops to zero as soon as the ABS light comes on. Diagnostics indicates a failure of the front ABS sensor, and the Check Engine light indicates bad data on the speed of the scooter. The front sensor was changed in an authorized service center. The problem remains the same and I don't know what to do anymore. The battery is new, the Vespa has only 2000 km on the clock. Everything is new. Please help. Thank you.

Does it have ABS? If so, maybe you have to recalibrate the ABS using the procedure in your owner's manual.

Would an ABS out of calibration result in the engine stalling?

You can't calibrate the ABS.

I guess he and or I meant ASR.

Exactly, my bad.

No. In particular not at an intersection as they mention when neither wheel is turning.

Drazen says the ABS light which is separate from the ASR indicator and the ABS light is only connected to the ABS controller whereas the ASR is code inside the ECU. So definitely a problem with the abs sensors at the wheels or the wiring from them to the abs controller.

The one of the most common causes of this problem is an incorrect gap between the sensor and the slotted tone ring on the wheel. This gap should be approx 0.5-1.5mm. Another common cause is a bent tone wheel causing the gap to not be within tolerance all the way around.

A bad battery could also cause it. Although Im assuming since the sensor was replaced that the battery might also have been checked by the mechanic at the same time.

So step one is to check that gap on BOTH front and rear. Use washers to adjust the gap. While checking the gap spin the wheel checking this gap all the way around.

Also using a diag tool to check the individual speed values when spinning the front wheel (lift the front of the bike) and separately the rear wheel.

I checked the battery. I'm an electrician. The battery is ok. Tomorrow I will check the clearances between the front wheel sensor and the reader. Diagnostics shows a failure of the front sensor. The situation happens on potholes and bad roads. When I enter the diagnostics in the engine computer, it reports an error about bad vehicle speed data and that's why it starts to lose power and jerks and the check engine light comes on. I'll get back to you with news. Hv

The ABS light, check engine light come on when expected wheel speed (one or both wheels) is wrong.

It is imperative that tire pressure is correct as I've noticed that when people complain about 'jerking' and 'cutting' abs cuts power when low tire pressure causes mistaken wheel slip (ie, wrong rolling radius). This is most apparent at speed over 100km/h or when nearing rev limiter speed. The speedo is already about 7%, now if your tire pressure is 40-50% off, which I see regularly then computer speed is off drastically and rev limiter cuts power prematurely.

The other thing is that on some earlier HPE models, rolling diameter was not set at the factory and is supposed to be set by technician during PDI (pre delivery inspection). If it is not set then you will see ABS light stay on.

Last thing I'll mention, to those who use home OBD readers, it is normal to see fault codes for speed sensor and the like since at the factory tests are conducted with rear wheel spinning independently of the front. The stored codes are from this event and I see it on every Vespa with ABS. I just erase the codes during first service.

After three visits to the authorized dealer and a couple of weeks without the scooter, I finally had to solve the problem myself. After all...the problem was a poor ground contact under the seat on the left side as well as poorly tightened battery terminals. When I removed the battery to test it, I noticed the battery terminals were badly tightened, and on further examination I found the ground terminal, which I assume is for the ABS system and must be for something else, because there are two wires on the ground under that screw. Thank you all for your support and help. Hey yeah...my high beam switch went bad in the meantime...when I turn on the high beams and want to switch to dipped...my lights go out completely. Then I gently flick the switch and the light works again. A HORROR MOVIE WITH MY VESPA.