Modern Vespa

Having put the bike (2016 Piaggio MP3 500 with 40k miles), successfully, through its MOT today, the engine management light decided to make an appearance on the way home from the testing centre (Sod's Law…).

Initially, the ASR light came on and a little later, the engine management light followed. I did have a sneaking suspicion that the management light was something to do with the battery voltage being low as I know, courtesy of the fine members of this forum, that the ASR light is temperamental where low battery voltage is concerned.

I arrived home in one piece and started to have a poke around. The battery voltage was approx 11.5v so I replaced that battery with the spare I have that I keep on a maintenance/tender charger. I'm confident that we can rule out the battery being the issue as my batteries are not old and I do keep them topped up.

Upon starting the bike with the fully charged battery, it became clear that there was an issue with the charging system as the voltage never increased when the bike was at idle (I used my multimeter to detect this), revved or rode up and down the street (I used the voltage display on the dashboard to see what was happening when I was riding and revving..).

I checked the fuses under the seat and they were okay for continuity (including the 30A fuse associated with the starter relay).

I followed the MO for checking the stator on the Partzilla website….

Stator Ground Test (Pin to Pin..)
0.3ohms, 1.1ohms and 1.0ohms

Stator Resistance Test
Open line on all three pins when individually associated with a ground point.

AC Running Test To Ground At Idle
4.2v, 5.5v and 6.6v

AC Running Test Pin to Pin At Idle
12v, 10.4v and 7.4v

I apologise for not providing any AC Running Test values while the bike is being revved. I was on my own and I just couldn't manage to acquire a value and rev the bike at the same time….

If anybody can help me resolve this situation, I would be most grateful and I'm happy to provide any more information that might be useful. To my mind, it looks like the stator or VR might have failed….

I had promised my Gran that I would visit her tomorrow but with the bike in this state it won't be possible. The sooner it's working, the sooner there'll be an old lady who is a good deal happier… Thank you in advance for your help

Sounds like one of the 3 AC legs on the stator has gone bad.

Far more likely is that the 'hidden fuse' has blown (or disconnected). This is a fuse between the regulator and the battery, and is hidden inside the connector on the starter relay - along with a more obvious spare.

Often, this is due to corrosion of the fuse contacts, which rapidly deteriorates due to the heat of the high currents involved.

Check this first!

Thank you for the responses, Gents. I'm really very grateful.

JimC- I've gone and had another look, just to be sure, pulled the hidden fuse out and checked/tested it in and ex situ and there were no issues with it. I then swapped it with a new one just in case and there was still no improvement. The holder it slots into appears to be in good condition too….

sbaert- would that be due to the difference in ohms values acquired from the Stator Ground Test?


Is there anything else I should look at? Once again, thank you.

Just to be doubly sure, did you check that you had 12V+ on both sides of that fuse with the engine off?

After that, it's testing for continuity between all three stator wires, and none to ground. Then test for AC volts with the engine running, you want to see 17VAC or more. If that's OK, but the volts at the battery remain stubbornly low, you have to suspect the regulator. Piaggio regulators normally fail short, providing far too high a DC voltage to the battery, but they can fail open.

Thanks JimC. Okay, I've been and double- double checked. I've taken some voltage readings from that area. I've removed the plug from the socket directly above the 30A fuse to get at it….

1) No voltage reading across the points of contact on the fuse.

2) A normal value but negative voltage value between the red and black cables attached to the relay when I connected the red multimeter probe to the red cable and black multimeter probe to the black cable (image attached).

3) When I clamped the red multimeter probe to the red cable and touched the two points of contact on the fuse with the black probe, I again got a normal value but negative reading. When I clamped the black probe to the black cable and touched the fuse points of contact with the red probe, I got a 0 reading on both points.

Also, I can't seem to get the bike to go over 200rpm when it is on the centre stand. Even when I get on the seat or double click the tilt lock I can't get it over 2000rpm. Is this normal?

Thank you

I'm gonna venture to say the bike is stuck in limp home mode.

Have you checked and verified all battery connections, and performed a battery load test?

If the battery is past 3 years, it is done for, with some not even lasting half as long.

These bikes are extremely sensitive to having clean juice and a good quality battery, not the generic stuff.

Unless you are dailying it, the only way to get max life out of the battery is to leave it plugged into a smart charger, such as a Optimate 4 whenever the bike is not in use.

believe it or no mate tenders do more harm than good to batteries, best way for a battery not on a bike is fully charge it then store it properly, then check the charge 6 months later, if on bike, charge battery, then check every month, if drained and not in use just top it up for a few hours, it is the best way to see if a battery is failing and not holding its charge. and batteries are a lottery some hold some die in months or years, always try to get the best quality battery your wallet can afford

Battery tenders are bad, yes. Smart chargers / maintainers/conditioners, no.

The Optimate automatically performs a battery check and test about 1 or twice an hour. If it is fully charged, it decouples itself automatically until the next cycle.

If the selftest shows the battery is not fully charged, it will top up the battery and then perform another test.

If the test shows the battery is sulfated at initial hookup, it will condition the battery and charge the battery at a higher charge to desulface the battery as best as possible.

See link for more details.

https://optimate1.com/om4/

Optimate marketing mate, I have had 2 optimate 4,s for my harley and Bmw, and know what they do, but trust me battery is better off the power than being left on, obviously useful if you do not have access to your ride all the time, garaged in a remote area

I've been using their stuff for a very long time, and battery life has been extended by a good stretch. So they must be doing something right, right?

I even once had a Yuasa batt that pushed 17 years.

FWIW, unplugged my MP3s battery status indicator shows the battery is no longer 100% charged even after as little as sitting overnight and that is with a brand new genuine Piaggio battery.

And battery life is also heavily influenced on how the battery was activated. If you just drop in acid and crank, you can kiss at least a quarter of the new batt's lifespan goodbye.

Thanks sbaert. I do keep the batteries topped up (I have a Noco and an Optimate and they've not diagnosed any faults with them…) and they are both under two years old. I have two because I also have a Yourban that I run around on but I can't really do the 300 mile round trip on it to pay my Gran a visit….

I will stump up the cash for a new battery just in case. I imagine that mine will have deteriorated should the fault be related to the VR or stator, in any case…

I should add that when I ride the bike, it goes well over 2000rpm (I got it up to 4000rpm on my short street…). I just can't seem to get it over 2000rpm when it is on the centre stand.

I load tested one of the batteries with a multimeter and got:

12.81v with ignition off
12.67v with ignition on and light on (my garage is dark so the light comes on…)
9.85v lowest reading when the bike was started
12.35v when running (light on again…)

That is not a true load test.

A real test consists of measuring the internal resistance of the battery, and how many Amps the battery is still capable of producing.

Just like in the movie Apollo 13, it is all about the amps. Voltage means very little if anything at all.

Having spent a while searching the forum last night, my stator readings appear to be quite similar to the ones posted by ponydrvr here:

Stator troubles

So, using the same battery, I get a voltage of 14.01 when the Yourban is at idle but only 12.50 when the MP3 500 is.

Would this allow us to rule out the battery with some degree of confidence? Both were running with the helmet storage light and front light on….

The only thing the 14.5V number tells is that the rectifier/regulator portion is working. End of story.

The numbers say zero about the SOH (state of health) of the battery.

looking like it is the starter relay, see thread below

Mp3 500 not Charging battery draning please help

I'm guessing that this might be what's causing the issue….?

Now all I need to know is who to get the exhaust manifold off to remove the flywheel cover. Or, is this not necessary?

Once again, thank you for the input, Gentlemen.

I thought that I would provide an addendum to this, should anybody encounter the same issues and find this thread useful later on.

It turns out that it was just the alternator that needed replacing and having rode for ~approx 300 miles since swapping it out, everything seems to be fine.

I checked the VR using the forward/reverse bias testing method and this showed nothing out of the blue. It's a simple test to undertake and it's worth doing while all the plastics are off, just to be sure.

To replace the alternator, it was necessary to remove the exhaust manifold and this proved to be a little tricky. The service manual states that you can do this from underneath the bike alas, I had to remove the plastics and come at the manifold bolts through the side of the bike with a flexhead ratchet spanner…

A few pointers….
I recommend making some specific 'notes' on the locations of the various screws holding the flywheel cover in place as there are quite a few different sizes. I made a 'model' flywheel cover (photo attached..) and shoved the screws through the cardboard model. Also, double check that the length of the stator wire that connects to the VR near the rear of the bike is sufficient before you actually fit the stator as mine was a tight fit and nearly didn't make it. I'm assuming it was just made a little bit too short in the factory.

All in all, it was a doable job for somebody like myself who is far from an expert on these matters.