Modern Vespa

Hey guys,

Just took my GTS out of storage where it was sitting for about a year and a half...charged the battery, filled it up...and too it for a ride.

Rides nice...BUT...There is one problem.

As soon as I accelerate past 10mph, the engine light comes on. When I bring it down to a stop (idling), the light turns off.

If I start riding at low speed (under 10mph), the light stays off, but as soon as I turn the throttle a bit, it lights up again.

Any ideas?

Other than that, the bike rides great. Excellent pick-up. Idles fine. I didn't notice anything weird.

I don't have a scanner and the local shop will probably want $80+ just to tell me what code it is.

Thanks in advance for the help!

does it have an oxygen sensor like cars catalytic converters? Sounds like its reading cats not working when throttling, but I have no experience with modern vespas.

I'm not sure if it has an oxygen sensor...perhaps someone on this forum can advise?

It probably does. Scooter West lists one:
https://www.scooterwest.com/oxygen-sensor-newer-style-2-wire-super-300-gts-300-639806.html

Now I'm not saying this is definitely what it is, cause I don't have an automatic scooter like that, but it sounds a lot like something I had on a stella 4t auto I was working on very briefly a few years ago. That thing had cylinder temp sensor and an exhaust sensor which the cdi used to provide the proper fuel mixture. One of those sensors would go bad and the warning light would come on. Same thing on a car, generally the check engine light is a warning about your cat system not working properly because an O2 sensor goes bad.

I can see a scenario where its working, but not great, and your throttle up is overloading the sensor causing it to get bad readings under throttle, but not under idle.

Just a guess from a non-modern vespa owner?

Here is some manuals that can help you if you decide to mess with it yourself:
https://www.vespaforum.com/manuals/Vespa/GTS300%20Super/

or this:
https://www.youtube.com/watch?v=D8_nBf0C424&ab_channel=VespaMotorsport

That Youtube video you sent seems to show the EXACT problem I'm having. Perfect match. I hope that's the case I'll grab a voltmeter and try to confirm this a bit later. Thanks for the tip!!

Regulator.

Diagnosing Charging System Problems

I would suspect the voltage regulator as others noted. I had the same issue. Do not use until fixed as the high voltage can damage electronics and sensors.

Robot's video posted above details testing for and fixing the regulator issue.