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xb12r blowing low beams and intermittent CEL

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young scooter

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Sep 29, 2019
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Greetings. Long time forum lurker but I need to ask some questions. I've had my 2008 xb12r for about 6 months now and have put 4000 miles on her. Been on 300+ mile trips without any issues. Bike has treated me well but I was wondering if you could help with a possible voltage regulator problem. I've done my homework, read forums, have a copy of the electrical diagnostic manual and I also have done the tests. All year my bike has not blown any headlight bulbs but OCCASIONALLY at night when I first set out for a ride I would notice my headlight get temporarily brighter for just a second or so and then go back to normal. Bike has also thrown a CEL code 16 twice this year but I chalked it up to drastic weather changes messing with the electronics (often was a 25+ degree change overnight). I think I've just been postponing the inevitable. I picked up my bike from the shop 2 days ago for a clutch job and I noticed the low beam was out. I pointed it out and he said they didn't mess with anything in the steering head. I took the bike home and yesterday i swapped in a new H3 silverstar into the low beam. Tested it out without the engine running, looked great. Later that night I had to move the bike and so i started the engine, moved the bike outside and left it running for a minute or two, then moved it back into the garage. Still no issues. this morning i wanted to give the bike a good wash after being in the dirty shop, I started the bike and once again the headlight was working. When i finished washing the bike and drove it back around to the garage the headlight was burned out again. I cannot confirm if this happened before or after I washed the bike. I used my multimeter to perform the following tests according to the electrical manual:
stator test, grab the 2 wire connector under the left side scoop and test each pin to ground. no continuity. set meter to amps AC and test each pin to each other with engine running, should be 20-28 VAC per 1k rpm. Its hard to hold the pins inside the connector steady while revving the bike and having it shake around but I got about 32 VAC on high idle (1200-1300 rpm) and somewhere around 60-70 VAC when revved up near 3K RPM. This confirms proper operation of stator.
voltage test: with bike idling at 1000 rpm voltage measured across terminals at battery is 14.1 or 14.2 VDC. REvving the engine up quickly, or holding RPM at higher revs does not seem to affect this figure much, it stays around 14.2 VDC. With engine off and cold the battery reads 12.5-12.6 VDC. This confirms voltage regulator output is ok.

I then tested the wiring at the headlight socket. I set my meter to ohms and checked OEM headlight ground wire to the engine block, and got 0.2 ohms. Seems to be good enough continuity. I then tested the power wire to the headlight with engine not running, full battery 12.48 VDC can be found waiting at the power wire. Just to be safe I ran a new ground since the OEM was looking a bit old and corroded. I installed a new bulb and checked for engine codes. I have a CODE 16 BATTERY VOLTAGE, which according to the manual is a faulty voltage regulator.

I am an HVAC student so I am fairly handy with running electrical tests and trouble shooting, but I don't know everything about these bikes. Given the intermittent bulb failures and the ECM seeing a bad voltage, I went ahead and ordered a new VR. Can anyone confirm with me if I did the right thing or do I need to run a different test? Thanks for your help.
 
lunaticfringe said:
Sire: i commend you on your outstanding trouble-shooting and excellent detailed synopsis of your symptoms and work performed. NOTE: your battery should be 13.2 volts fully charged at rest with no parasites leaching voltage from same. i mention this as i suspect your VR, according to your posted figures, is putting out 15.0 volts or slightly higher as the motor runs thru it's rev range but your multi-meter showing a tad less volts. its accuracy might be a tad suspect.

I went ahead and ordered a new VR. Can anyone confirm with me if I did the right thing


you did the right thing. i'm now seeing these single phase 2008-2010 VR's fail at an ever increasing rate and not sure why.
take a few minutes during new unit installation and be sure you have a nice ground between the VR and frame. prolongs life.
Click to expand...

thanks. Is that 13.2V with engine off? Because 12 volt nominal systems are supposed to be 12.6V at rest, just like a car. Or is it 13.2V at hot idle? Thanks
 
I have never seen/heard of this before, are you sure of this? automotive batteries tend to be 12.6V at rest, I've never heard of 13.2 unless it is a buell-specific figure
 
So are there any other common symptoms associated with a failing VR aside from blowing low beams? Because my symptoms have been pretty tame so far
 
The voltage spike you are seeing (headlight getting brighter) is a very common sign of a VR on the way out. If you had a DVOM connected at that moment you could see 16V or higher:upset:

IMO, 13.2V at rest is a bit, uh... optimistic. 12.6V is fine. There's nothing special about a Buell 12V battery or charging system other than the engine needs a LOT of amps for cranking. A 220CA minimum battery is recommended:eagerness: DEKA is a good brand for a regular Buell battery. I have also had great experience using a Li-Ion with no charging system mods.

I also commend you for proper diagnosis, and a clear description of the problem! Thanks for the Deets:angel:
 
Cooter said:
The voltage spike you are seeing (headlight getting brighter) is a very common sign of a VR on the way out. If you had a DVOM connected at that moment you could see 16V or higher:upset:

IMO, 13.2V at rest is a bit, uh... optimistic. 12.6V is fine. There's nothing special about a Buell 12V battery or charging system other than the engine needs a LOT of amps for cranking. A 220CA minimum battery is recommended:eagerness: DEKA is a good brand for a regular Buell battery. I have also had great experience using a Li-Ion with no charging system mods.

I also commend you for proper diagnosis, and a clear description of the problem! Thanks for the Deets:angel:
Click to expand...

Alright thanks. The reason i spent all this time typing that up is twofold: first, i dont wanna waste time with messages telling me to test this or that when i already did that test. Secondly, i want people in the future to he able to follow along and self diagnose. Tired of finding threads that are dead ends
 
fortunately for me, I have never had a dead battery issue. I suppose that would be coming down the pike if i kept delaying this repair long enough, however
 
I think I was lucky in that the VR didn't overcharge the battery but rather just stopped charging.
Some of the members installed a small led voltage gauge on the bike so they get a constant read out of what the VR is doing, that's next on my list to do.
 
Last edited:
There was someone who posted a cool LED bulb that would be Green for resting and charging (12.0-14.8) and Yellow for under voltage (<12V) and Red overcharging (>14.8V). I thought it was perfect for a charging system check at a glance on the road. No tiny digits to read, and a clear indicator for a intermittent problem. After all you don't really need to know the exact voltage at that time, just that theres a problem to look for.

I can't find it now but I thought it was an awesome idea, and easy to install. Theres even an extra bulb hole in the dash.
 
Thanks. I ordered that voltmeter, I am gonna do that mod. Any ideas on how to remove the gauge shroud from the firebolt?
 
Thanks. You reccommend installing LED backlights while i am in there? I read somewhere someone got light "hotspots" from doing that. The light didnt diffuse well. Sound about right?
 

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