Autonerdz forums

This one came to us as MV Agusta agents from another garage after having been looking into it for almost a month after initially it was taken to the customers local garage to have a battery replaced.

When the tech fitted the battery and started the bike up he noticed that the starter solenoid had a rapid pulsing action when it was activated, rather than a steady on, hold, and off.

Initial they replaced the battery again, the starter solenoid before having the bike transported to us for further checks as they could only see that the ECM was the next faulty part.

The bike is an MV Agusta Brutale 989, the factory provide very little service info about the system other than the whole vehicle wiring diagram which i found online as it wasn't available on dealer portal.

From my understanding of the system, the start button the rider activates to start the bike switches a voltage to the ECM to let the ECM know to start the vehicle as long as all other conditions are met. The Computer then controlls the earthing of the starter solenoid winding's directly (with no other circuits included on this signal wire). The ECM has a timed system, as best i can tell, so given a no start situation the ECM only allows cranking for a given period of time.

I found the same symptoms when starting, the starter solenoid would pulse/rattle when activated. Although given this, the bike always started fine within a couple of revolutions and ran and drove well.

This is, by my and the other techs experience, an unusual way to activate a starter solenoid, from our experience with motorcycles at least. We both surmised that this rapid pulsing of the solenoid contacts would shorten the life of the solenoid considerably as a minimum.

We happened to have another Bike in the shop with the same ECM system which we were not aware of any faults with.

I started by scoping the triggered wire from the ECM at the solenoid on the faulty bike and found the waveform as posted. Batt volt with pulsing signal at regular 100ms intervals with ignition on, engine off, not cranking.

Under cranking the signal has the same signal but drops to ground between pulses. Hence giving the pulsing of the starter solenoid. Unusual we thought so carried out the same test on the other bike in shop with no reported faults. Exactly the same scenario.

Our conclusion is currently that this is a normal "feature" rather than a fault of the bike given that both bikes are identical and have no other reported faults. We suspect the pulsing is possibly how the ECM references time to establish when to stop cranking given a no start scenario.

I would appreciate any input or other thoughts if anyone has come across a similar system or issue before. The customer has taken the bike back and advised to report any future faults or symptoms if they present themselves.

Yea thats kind of what we thought, someine on the R&D teams unique idea. It seems to work fine and cant say i have replaced alot of solonoids yet but just interesting to find as without the other bike to test against you could quite easliy assume a fault there somewhere and get expensive real quickly.

How do other vehicles with ECM controlled starter activation calculate time allowd to crank before they shut off in a no start situation?

I agree about security system

Also it may stop someone accidently hitting the start button when the engine is already running

The pulse could be a self test to see if there's continuity with the starter solenoid.

Did you by any chance do a current draw test on that solenoid? where's that wiring diagram?

what a useless diagram, totally Italian!!

see item 45?? anti theft connector

From what I can make out, there's 5 wires

-battery cable
-cable to starter
-ground signal from 1 CPU
-another battery supply to the 2 bottom connectors*not sure what's it for
-43 service control unit,  37 light switch** somehow it comes from the ignition switch but it's not very clear

sorry that's all I can make out