if the Optimate is passing the battery, I'd not be looking there. I have an Optimate too, and my original batteries have lasted 10 years with life on the Optimate.
You didn't do the very first step in the diagnostic process - UNPLUG THE PC5. Well know for having issues if wet.
The process that should work for your bike to get into diagnostic and check the codes is as follows:
1) Set the kill switch to "Off"
2) Press both dash buttons together and then turn the ignition on. Hold the buttons for about 10 seconds until the display clears and either "Co" or "Diag" is displayed.
3) If "Co" is displayed, (as it would if you had last adjusted the Co settings), press the left button to swap it to "Diag".
4) Now press both buttons again for about 3 seconds and "d:01" will appear where the clock was. On top of this a number will appear to the left of it, (where the ODO is). This number is the fault code if any for that specific function. Each d:XX has it's own particular part of the bike that it reports on.
5) Now press either the left or right buttons to scroll through d:01 to d:70, (there are gaps). Both buttons do it, one simply goes forward, the other backwards.
6) The Diags we are interested in are d:61 and d:62. 61 is the list of codes present, 62 is the number of faults and the clear faults one.
7) Scroll through until you reach d:61 and watch. If any number of other than 00 appears, then you have fault codes reported. These are historical so you may have more than one code if the old codes were not cleared after a previous issue. The reading will slowly scroll thru all the fault codes present if there are more than one.
Common codes are 14 (blocked or open air tube), which is the vacuum hose that connects the throttle bodies and we use when syncing them. The caps get old and crack, leaking air into the system, (and water during heavy rain), which can cause a number of issues, and throw this code. Oil in the airbox drain tube can sometimes also cause this if it's excessive. 69 is wheel sensors, sometimes triggered if the magnetic sensor comes in contact with metal when out for a wheel/tyre change. 30 is the lean angle sensor and will show if you've had the bike on it's side, which is not so uncommon.
80 Move on to d:62 after recording your fault code(s). d:62 will show the number of codes present, (1, 2, 3, etc., not the code numbers). Now turn your kill switch to "Run". This will reset the codes to 00.
9) Turn the ignition off. You exit diagnostic mode and upon next key on, the dash will read normally. If you have issues that have not been corrected, the codes will re-occur the next time you run the bike. Some codes will take some riding time to appear, others appear immediately.
Hope that helps M8, but I'd unplug that PC5 and go for a ride first before letting Yamaha have a go at it.
