Monster S4RS 2006 check engine light

[sammute]

Hello! I've posted a year ago about weird issues of S4RS check engine light. Looks like it's never ending story.

Patient is 2006 S4RS with full Termi kit. I am second owner of this bike. Every ride after few minutes from start check engine light goes on. For last year couple of guys tried to find what is the cause but for now check engine light is a winner. First error was open circuit on left fan and it was solved. Second was error of starter diagnosis but I had to change tycho so it was also solved. Now it shows random errors, sometimes can error and very often "unknown error". My mechanic said it may be problem of battery so I've changed it and guess what - check engine light is still there. Any ideas?

[stopintime]

Got it diagnosed by a dealer?

[sammute]

Yeah, they have no idea

[Duck-Stew]

Some of the Monsters from that era experienced a random short due to how tightly the factory ran the harness up around the steering head.

Maybe?!?  I know it’s a straw to grab at, but it is something...

[Howie]

What codes did your mechanic retrieve?

[booger]

Weird electrical problems are one symptom of a failing rectifier/regulator. If you haven't yet replaced it, you probably should. My bike would just stop running and all lights on the cluster would light up. Get a MOSFET part. I have a Rick's Motorsports brand but I think Ducati has now gone to MOSFETS and there should now be a viable OE Ducati replacement. A colleague has an S2R and his R/R went out. He got the Ducati part. I have an S4RT and I have a Rick's Motorsport. Works fine no issues.

[OrangeDragon]

I have had this same problem with my 695.  The check engine light always stays on.  I have had two dealers check it out with no luck.  They have said it is maybe the health speed-o-healer and/or gear indicator I installed but those were installed before the check engine light started staying on.  I have tried disconnecting the gear indicator but that didn't change anything.  I haven't tried to disconnect the speed-o-healer.   There is zero issue with the bike so I just live with the check engine light on.

[itsamonster]

The rectifier on mine caused some weird symptoms including damaging the battery.
A shindengen mosfet sorted it. Along with a Shorai battery, which lasted 4 years. Switched to a shido which has inbuilt cell balancing.

[sammute]

Well - after the last check:

- check engine sometimes shows up, sometimes no
- no errors in history
- unknown error when check engine is on
- rectifier is good, stable 14,1/14,2V

[booger]

Well - after the last check:

- check engine sometimes shows up, sometimes no
- no errors in history
- unknown error when check engine is on
- rectifier is good, stable 14,1/14,2V

Rectifier can test OK but still be bad. You only see the symptoms when they get hot and start glitching out. Just spend the money and get the new MOSFET design either from Ducati or Rick's. I think it will solve your problems. Mine used to do similar, I switched the rectifier out, no more issues. It really doesn't need to be a protracted investigation. Everybody here knows those R/Rs are garbage.

[Howie]

Big problem is the regulator is not in the air stream.  On the older bikes, if connections are kept clean and tight they often live a long time.  My old 750 (2001) that I sold four years ago with over 80K miles still has the original regulator.  The upgrade to a mosfet is a good idea on that bike, but proper diagnosis is essential.  Yes they can and do act up with heat.  Ride around with a voltmeter attached and observe the voltage.  Oh, also have the battery load tested.