DIY Diagnostic tool for injection Vespa's with MIU ECU
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Vespa GS160mk1 / Vespa GTS300 super / Vespa LX50 4V
Joined: 26 Nov 2016
Posts: 28
Location: The Netherlands
Sun Nov 27, 2016 1:46 pm quote
I have noticed that there is a lot of information about the older carburetor Vespa engines on the web but hardly anything about our modern injected Vespa engines. Because a lot is controlled from the ECU it's often vague when dealing with injected engine complaints.
After a lot of googling I found out that there is a lot of information for the other injected Italian bikes (Ducati and MotoGuzzi) but hardly anything for our injected Piaggio's. Their information is very useful so I have combined it in this Vespa tutorial.

There are actually 2 programs (freeware/donation) that should work with the Magneti Marelli MIU ECU placed in our injection Vespa's.

These are IAWdiag and JPdiag (in this tutorial I will use IAWdiag).

I've tried IAWdiag and did some tests with my '14 GTS300 (MIU3G) and a '09 GTS300 (MIU1), both are communicating fine with IAWdiag.

So if you are interested in a such a diagnostic tool, check your ECU and see if it is compatible with the program.

On the side of the ECU you can find a sticker with the type/serial number of the ECU.
The picture below shows a IAWMIU3G ECU (2014 Vespa GTS).

Here is a list of compatible (selectable) ECU's in IAWdiag
If your ECU is in the list then IAWdiag should work.

What do we need to build our diagnose tool:
- pc/laptop with Windows XP and higher
- VAG KKL cable (preferred with FTDI chip)
- Fiat OBD cable
- Multimeter

To start with the pc/laptop. I run IAWdiag on an old Windows XP laptop from 2004 and a Windows 7 starter Netbook from 2009, so the specifications are very low and the older pc/laptop will do the job.

About the cables: To start with the VAG KKL cable, I have bought two of them and only one is working fine. Both bought on eBay but they sell them on Amazon as well.
The first, not working one, has a cheap Chinese CH340 chipset. The other cable has an original FTDI chipset and is working great.
You can find this item on eBay (item 161743974836)

The second cable is a Fiat OBD cable with 2 crocodile clamps (red + and black -).
You can find this item on eBay (item 252433646626)

IMPORTANT: check the correct wiring of the Fiat OBD cable. It should be wired according the scheme below. If this is not the case you can damage your ECU.

When you have all the items mentioned above you can start the installation.
Install the FTDI drivers before connecting the VAG KKL cable.
Don't use the drivers from the disc that comes with the cable.
Download the drivers from the FTDI site (

On a Windows XP/Vista machine these are the correct drivers:
On a Windows 7 and higher these are the correct drivers:

When the drivers are successfully installed you can connect the VAG KKL cable to the pc/laptop. The new hardware is found and should work accordingly.

Check with the following program which COM port is dedicated to the VAG KKL cable.
You can also change this COM port if necessary. In the picture below you can see this cable is installed on COM9

Now you can test the VAG KKL cable with the following program.

Connect the crocodile clamps to the battery (connect red clamp first, then black).

IMPORTANT: do not connect the diagnose plug/connector.

Start the AdapterTest program, fill in the COM port and press "connect".

When test 1 and 2 are successful press "disconnect".

If the tests are not successful, then there is something wrong with one of the cables. Do not connect the cable to the ECU to prevent any damage. Check again the scheme of the Fiat OBD and open the VAG KKL cable to see if there is not a fake FTDI chip installed (like my first Chinese cable).

If the tests are ok, both VAG KKL and Fiat OBD are ok, and you can connect the diagnose plug/connector.

You can now start IAWdiag, fill in the language, COM port and ECU type.

Go to the upper left en press "file" - "connect" and follow the instructions on your screen.
When the ECU is properly connected you can find the data of your ECU on the bottom left of your screen. You can now select the parameters you want to monitor, read out the fault messages or do some static tests.
You can also start your engine to read out more parameters.

IMPORTANT: Don't do a TPS reset. These ECU's are pre calibrated at the factory.

Source: Vespa GTS300 2015 ABS workshop manual (page 199 & 200):
Source: Vespa GTS ECU:

When you want to quit and your engine is running, use the "kill switch" to turn off the engine.
Then go to the upper left en press "file" - "disconnect" and follow the instructions on your screen.

So far the information how to make your own diagnose tool. I hope that this tutorial is useful to many modern (injected) Vespa riders and enjoy your own DIY diagnostic tool.

Extra information: The IAWdiag software designer has made another program called IAWMIU3GReader, IAWMIU3GWriter and IAWMIU3GEEPROMTool. With these programs you can read and write to your MIU ECU so it should be possible to adjust your mapping.
They can downloaded from:

I did download my ECU map (.bin file) and my EEPROM (.eep file) as a backup. I also imported the ECU file in the mapping program TunerPro ( to see if it's recognized, and it's working in combination with the .xdf file from:
Mapping is to complex for me, so I stopped further testing. Maybe there are people on Modernvespa who are interested in this feature.


JPDiag ( is also working with the ECU's listed above.
Tested with the same cables and windows drivers from the tutorial above.
IMPORTANT: test the Fiat OBD and VAG KKL FTDI cable by following the tutorial above to prevent damage to your ECU.

Install JPDiag and follow the installation instructions.

Connect the USB cable to the pc/laptop
Connect the clamps to the battery (connect red clamp first, then black)
Connect the diagnose plug/connector.

Start JPDiag and select your preffered language.

Select the correct cable. If you use the FTDI cable from the tutorial above, select Galletto Cable and press "ok"

Press the lower radio button on the right side of the "connect" and press "connect"

The ECU is now connected and you can see the ECU information.

To get a free license press the blue "copy" button.
This button will automatically open your browser and connects to the JPDiag webpage (, fill in the scooter type and email address and you'll receive a license file by mail.
Copy cle.lic file without renaming it into JPDiag directory, usually it's located in c:\program_files\jpdiag\

Restart JPDiag and you can use now all the features.

If you want some more information about the Magneti Marelli MIU G3 ECU you can check the .pdf document below.
The document is written for both single as twin cylinder bikes (MotoGuzzi V7) but the MIU ECU basics are the same for both so you can use it as reference.

Last edited by Pilaf on Thu Dec 22, 2016 7:22 am; edited 8 times in total
Molto Verboso
Joined: 06 Jun 2013
Posts: 1011
Location: The Twin Cities of Minneapolis/Saint Paul, Minnesota
Sun Nov 27, 2016 1:54 pm quote
Fantastic! Thank you! Thank you!
I can't wait to try this out!
Sportcity 350ie
Joined: 08 Nov 2016
Posts: 43
Location: Zagreb/Croatia/EU
Sun Nov 27, 2016 10:36 pm quote
Great job! Thank you;-)
2009 Piaggio mp3 500ie "Ephie"
Joined: 18 Apr 2012
Posts: 232
Location: Denver CO
Mon Nov 28, 2016 7:12 am quote
I wonder if this will be compatible with the earlier mp3 500s
Vespa GS160mk1 / Vespa GTS300 super / Vespa LX50 4V
Joined: 26 Nov 2016
Posts: 28
Location: The Netherlands
Mon Nov 28, 2016 10:55 am quote
Olestra wrote:
I wonder if this will be compatible with the earlier mp3 500s
Should work if this information is correct: MP3 500 ECU version?
In the mp3 topic they are talking about MIU and IAW15P ECU, they are both in the list of IAWdiag.
GTS 300 SuperSport
Joined: 06 Apr 2017
Posts: 2
Location: Germany
Thu Apr 06, 2017 12:37 pm quote
Great Tutoraial! I just installed the programm and read my MIU1 GTS300 - all working fine. Im just wondering how I could read/write this type of ECU. I found the MIU3G reader & writer but unfortunately not the programm for my old MIU1.

Did anybody try some mapping on our Vespas with this programm?
Vespa GS160mk1 / Vespa GTS300 super / Vespa LX50 4V
Joined: 26 Nov 2016
Posts: 28
Location: The Netherlands
Fri Apr 07, 2017 9:48 am quote
When you are you using JPdiag sent JP a mail and ask him about the price (payware) for a single reader/writer licence for the MIU1 version.

About the mapping, i'm still in the expirimental phase and learning how and the meaning of all the parameters in the mapping. No experience on the MIU1, only MIU3. What I'm most interested in is the difference between the Euro3 and Euro4 mapping. I downloaded both mappings (2015 & 2017 GTS300) and as far as I can see the mapping of the Euro4 is overall "leaner" so that explains the little loss in horsepower.
GTS 300 SuperSport
Joined: 06 Apr 2017
Posts: 2
Location: Germany
Fri Apr 07, 2017 2:02 pm quote
Ich would really like to do some setting on my vespa. Will reader about jpdiag and ask him if He can help me. The MIU G3 reader/writer doesnt work on the MIU G1. Thats what I already found out.
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