Modern Vespa

Soooo just got the GTS serviced, new tire, drove it a couple of days and it's been running great. Today, shortly after filling up in the morning my engine light came on. No loss in power, running smooth. I would say it's 100% if the damn light wasn't on.

Trouble is I was planning to put about 300 miles on it today, and now I'm nervous. Anyone have any thoughts?

Don’t ride it any more than you have to before getting it checked out by your dealer. It could be something simple or it could be something a bit more serious. You just don’t know.

Did it stay on?

Could be as simple as a loose connection on the O2 sensor.

Yeah, trouble is my dealer IS 300 miles away. Going to see if the local Powersports place can read it, but I'm not going to hold my breath.

It did. It has come on a couple of times before briefly. The dealer ran the history when they serviced and it just showed the ECU recalibrating. It usually accompanies a change in elevation, which it kind of did today but it's my usual commute and this is the first time. More humid this week than ever before.

Related note, anyone know if this'll work for reading the codes? Or know how else to do so? Don't always want to drive 5 hours and back to read or reset it.

https://www.amazon.com/dp/B07S85FNV4/ref=cm_sw_r_cp_apa_glt_fabc_EH351W0YKH19GE65THDV?_encoding=UTF8&psc=1

I had the same problem and it was also intermittent. What happened is that some of your contact connections to the computer, oxygen sensor, etc. have become oxidized. They operate at 5 volts and must be absolutely and totally free of any fouling.

Buy some Caig's contact deoxydizer and clean up every connection you can with it, including the big one attached to the computer. It's been a year since I did mine and it has worked flawlessly. I have no financial interest in the product.

Here is the link to it on Amazon.com

https://www.amazon.com/CAIG-LABORATORIES-D100L-25C-Contact-Cleaner/dp/B0000YH6F8/ref=sr_1_8?crid=1RNN1L1Z13449&dchild=1&keywords=caig+deoxit+d5&qid=1627553272&sprefix=caig%2Caps%2C190&sr=8-8

That should work.

But I'd recommend a bluetooth solution so you can use your phone and take it with you. See that cable in the lower right with the red+black clips? you'll need that for your classic gts (different for an hpe). You'll also need a 'bluetooth elm327 obd2 adapter' (search amazon/ebay/aliexpress).

suggest reading these two MV posts:
GUIDE: How to read Engine Fault Codes (OBD/OBD2)
DIY Diagnostic tool for injection Vespa's with MIU ECU

note: guzzidag and jpdiag on the cd/dvd in the pic are free apps.

ive had this with my gts a few times too. unscrew the gas cap, and very lightly screw it back on, drive for a bit again, itll go away. gotta go light with the gas cap, to let the vapours out apparently

+1 on the gas cap, especially after you refilled it, leave the gas cap open to vent or suck some out -- also, you should only be putting 93 octane in there vs regular

I do put 91, anyway - Best I can do where I am.

ok pretty close, maybe a batch of bad gas or the o2 sensor for sure would be my first guess, I had this happen before and rode it until it went away after the next refill.

However, check the two oils and coolant levels to be sure

Wait, two oils? What's oil number two?

Engine Oil has 1300cc's and Hub Oil has 250cc's

Note: Low oil level is something that certainly needs to be checked. However, it is generally not a cause for the check engine light to come on. The check engine light comes on when an electrical / electronic issues in the engine management system. Which is why the gas cap / o2 sensor is the main suspect.

Yup yup, I'll look up how to check hub oil. I figure gas cap too but wasn't gonna ride 5 hours on the guess.

Same problem here as well. When it starts acting up and coming on and off I say the Act of Contrition in Latin and I do the sign of the cross

Reseated the gas cap a little less snugly and it turned off ~35 miles later. Diagnostic tool will be delivered today for next time's peace of mind.

Nice glad it worked out.

Which diagnostic tool did you order? I was lead to believe that was a proprietary tool that only Vespa dealers had access to.

I ordered the one I linked above that is technically for Ducatis using the same ECU. It's not like the PADS, but it will read and clear codes.

HHmmm interesting, you can clear most all codes by troubleshooting and fixing the common problems, clearing the code and light without fixing the problem only makes the light come back on -- be very careful, those widgets can easily blow your ECU and then that will cost some serious cash to replace.

Yep, I'm gonna hit it with the multimeter and test it on the laptop end first before it ever touches the ECU plug. That being said, I didn't mean that I was just clearing the light to clear it. I just want to know if "Check Engine" means loosen the gas cap and chill out or start watching Robot vids. I've had the light come on three times now (in 7k miles) and it's always gas/vapor/elevation change/fillup related.

Aww I see, I think the issue you are having is that the GTS has a high compression engine and you need a Higher Quality Fuel at a Higher Octane to resist Fuel Detonation.

Detonation is a result of heating and compressing fuel and air until they ignite before the spark plug is turned on. A higher octane fuel can handle more heat and pressure before combusting.

On modern computer-controlled Vespa's with fuel injection, the computer is constantly monitoring fuel trim and detonation and making appropriate adjustments in the timing and fuel air mixture to compensate for engine knock.

Because higher octane gas burns slower, it is more resistant to knock when subjected to higher RPM and cylinder pressures. Compression ratios also factor into cylinder pressures. Higher ratios cause higher cylinder pressures and therefore cause the engine to be more susceptible to pre-detonation or knock.

My vote would also be a fuel cap related issue. My BV has this issue sometimes and reseating the cap typically fixes it. I can't see the fuel level when filling up (not sure how the GTS is set up) so it sometimes overfills as well which will cause it to light up for a period as the fuel evaporates.

That is WRONG. Vespa engines do NOT have a knock sensor. It's up to the rider to provide adequate octane fuel.

You are correct that there is no knock sensor.

Never said there was, just explaining the issue that octane rating is basically the measure of a fuel’s ability to resist knocking during combustion, caused by the air/fuel mixture detonating prematurely in the engine.

There is only the Oxygen Sensor Lambda Probe that is linked to the computer, which adjusts the fuel/air mixture and engine timing to compensate for any changes in the oxygen level and optimize the fuel/air mixture to prevent knock.

Bottom line: Low quality fuel with low octane is the main culprit for the caution light coming on here.

No. Strongly disagree. The octane is not in any way, shape, or form related to the check engine light. No, no, no.

lol I would strongly disagree with that

Agree to Disagree

Low octane in high compression engines = air/fuel mixture detonating prematurely in the engine = check engine light

This is not a case of agree to disagree. Octane is not the culprit here.

ok let me phrase a little different here.

The Oxygen Sensor Lambda Probe is causing the check engine light to come on, which is caused by low quality fuel with low octane in high compression engines = air/fuel mixture detonating prematurely in the engine = check engine light

No.

I ran regular unleaded for the first 5000 miles that I had it, in my ignorance.

Uh...light never came on. Two of the three times that CE has come on have also been at points with sudden changes in elevation - so much so that my tire pressure sensor light comes on in the same area in my car.

I recant my low-octane ways in a "longevity and strength of the engine" sort of way, but I'll be deferring to Jess on it not being the cuplrit for the light.

What is this then? HTF could it compensate for engine knock if it didn't have a knock sensor? Therefore you were implying it did.

Agreed. Low octane in no way will set off a check engine light.

Not to necro, but this is still an intermittent issue. It's been driving me crazy going on and off, but generally shuts of everytime I find the time to set up the jury-rigged code reader.

If it means peace of mind, does the PMP show what the code is? I'm not against installing it - I have a usb port there now, but I basically never use it.

Anyone have thoughts? Being able to ship out my phone and immediately diagnose is sounding pretty good to me, even if the PMP is otherwise gimmicky.

Don't think pmp will help with this.

You need a obd2 reader

I have found that on my 2018 GTS the check engine light will come on after I have filled up gas sometimes and then after a few days will go away.
Based on the wisdom of the forum I gathered that it possibly was a function of the evap system. It hasn't affected performance and I don't worry about it, if it stayed on even after a few miles of riding I'd be concerned.

Trenchleton

On my 21 Vespa GTS HPE, I overfilled up on a hot day not paying attention and got the check engine light immediately, opened the gas tank to relief the pressure a few miles down the road and it went out after another 30 miles or so. Then pretty much every fill-up after the light would come on and I started to feel like I was losing power on takeoff's and figured it had to be the EVAP so decided to remove it, vent the fuel overflow through the bottom and cap the hose to the intake manifold. Noted: When I removed the cannister, it was full of gas which is what was causing the problems. After I removed and put back together, without the EVAP, the check engine light went out and power was restored with the issues never to come back. Noted: The 2019 models in the USA and up have the new ECU so not sure about the long-term effect, but a bunch of us in our group have removed them off the HPE now so think we'll be ok.

Directions below

Great photos....maybe we could get that in the wiki for better reference?

I appreciate the suggestion and guide! Do you know if it is possible to also just dump the canister if it gets gas-logged without removing it?