A fun three days.

ECM, BCM. No fuse box, no starter relay.

The fuses, all multimetered fine.

The BCM Cable.
When I attempted to start my Sportster three days ago, it gave only two cranks. The lights went out, the speedometer faded, all power gone. Then, the lights came back on, and it has since refused to start. Generally when you press the power switch you hear a high pitched whine, the fuel pump I believe. Then, when you press the ignition switch, the starter will crank (or attempt to). Thing is now, there is no crank. The ignition switch will simply make the same fuel pump whine until I stop pressing it. The diagnostic code I am receiving is "B2121", which is "Starter Output Open/BCM Malfunction". Since then, I have begun my bizarre journey into diagnosing the 2015 XL1200C which for whatever reason has no fuse box, and no starter relay. I'm fairly certain that something in the BCM committed suicide. Since its death would run me about three to four hundred dollars, I come to you folk in hopes that I'm missing some hidden wizardry that I simply don't understand yet.
Here's what I've tested so far: The battery is fine. It's a Lithium battery, not even a year old. It passes the load test, but even ignoring that I have another bike that starts fine that I hooked jumper cables to. Hooking them to the battery produces the same effect, as does just hooking the jumper cables to the terminal wires themselves with no battery. Battery is certainly fine.
Generally with this kind of issue, the first recommendation is to check the "starter relay", or maybe the fuses. But this model doesn't have those. There is no relays, and there is no fuse box. Dumbfounded the people at the dealership, even with their 3D diagrams. You can see in the second image that directly to the left of the battery is the BCM unit, then to the left of that is the ECM. That is all. There is a small fuse cluster at the end of a cable (third image), it contains a 40A main fuse, 15A P&A fuse, and a 10A Battery fuse. All of these fuses are functional, they passed connectivity on my multimeter and have no resistance. It shouldn't be them either.
Power should be capable of running through the starter. Putting a positive jumper cable on the starter terminal causes it to spin, so the starter is certainly capable of receiving power. The starter, excluding the grounding cables, receives two cables: the power cable straight from the battery, and the starter solenoid trigger cable that comes from the BCM. Testing these with the multimeter, the starter solenoid cable has a complete circuit with ground, all the way up the L2 port on the the cable that plugs into the BCM (fourth image). The cable is not damaged, it does not have this ground when it is unplugged from the starter.
I have no reason to assume that there is anything wrong with the starter in particular, and I have no reason to assume the starting switch on the handlebar is bad as it clearly interacts with the fuel pump, and causes the BCM to give the red light when pressed. I don't think there is anything wrong with the starter trigger cable. The only things I haven't had the opportunity to really test is that the power cable straight from the battery to the starter doesn't have a bad ground since I haven't disconnected both ends, and that there isn't anything wrong with the grounds on the bike. Neither of the grounds are loose, I can guarantee that, it's just really difficult to remove them without beginning to disassemble the engine as well. I did attempt to measure the starter power cable and it did give me a reading of 12, so I assume that means it's not losing power from a bad ground somewhere.

If there's anything you think I'm missing, I would be happy to try it, and I'm willing to provide photos of anything you need to see. All in all, just the nature of it starting to crank, losing all power, then coming back on with an inability to complete the starter circuit just makes me thing that the BCM died for some unexplainable reason. But I want to test everything possible before I replace it.

 

Sorry can't read that wall of words. Got to no fuse or relay.

Most of or pretty much every electrical function is powered by the BCM in some way. It is because of that there is no major fuse box or starter relay.

Wiring diagrams here - 99949-15_en - 2015 Wiring Diagrams (harley-davidson.com)

You need to start from the beginning with firstly a known good battery that can start a Sportster. Don't assume anything on that point.

You need to ensure all of the connection points are clean and tightened to the HD spec. Tight is not an indication they are done up correctly.

For the code I can find no indication that it is for BCM malfunction only the starter is open circuit somewhere.

It is very easy to test the starter on the bench. I am not absolutely sure on the bike. You can test the solenoid by putting 12 volts where the little Red / Black wire connects to it.

 

I read your message. You tested the starter, it spins. The solenoid engagement starts with pressing ignition switch, it gets routed to BCM then out to solenoid. If ignition is working and solenoid is working the it's either the BCM, or wiring between the two.

 

The BCM is part of the starter circuit, so the break in the circuit being in the BCM is very much a possibility, that's why it's listed as one of the two meanings for the error code. After testing the cables, that seems to be what it is. The battery I attempted to use for jumping is in an Electraglide, so it should be capable of starting the Sportster. The rest of the Sportster's systems act like they're on full battery in both scenarios so I find a battery problem to be unlikely. I tested the Starter Trigger cable again, however. I get a complete circuit when touching both ends of the cable, and I get a complete circuit all the way to the negative terminal of the battery when testing the end of the cable that plugs into the BCM while it's still plugged into the starter. Vice versa did not work, testing the part of the cable that plugs into the starter had no complete circuit with anything when plugged into the BCM. I know it's not the cable, and the power to the BCM wouldn't be the problem as every other system in the bike functions with no error. Unfortunately it has to be the BCM. Thank you for the advice, even if you didn't bother to read what I said first.

 

Thank you for the advice. Seems to be the BCM, I have a complete circuit all the way up to both sides of the BCM itself after testing the cables. I'm going to make a last attempt to not spend several hundred dollars and disassemble the BCM to see if what's broken inside cannot be replaced. Wish me luck.

 

1. Battery should read 12.8v or higher after a charge. 12.6v is the lowest reading that begins with a recharge up to 12.8v or higher off the charger.
2. With the voltmeter set on the battery, starter draw should show 11.1v and return to 12.8v after starter button is pushed.
3. Meter should show 14.4v when idling. So keep your eyes on the meter all the time to read these quick numbers rotating once running.

Just for grins:
a. Scrape away lead at the battery posts.
b. Scrap away fresh metal off the one side that touches the battery post sides of the cables.
c. Use a jumper cable at the ground of the battery, 2nd jumper end to the frame, positive cables from engine to frame. This shows a good ground with the 4 jumper ends from battery ground to the engine to frame.

You mentioned 12v without stating the decimal point after 12. A well charged battery should read 12.8v statically after a day or two off the charger.

The load test or bench test is that the motor turns over the engine. So a direct positive jump to the starter motor shows good as if a literal bench test was performed without removing the motor from bike.

Signed,
NOLTT (no one listens to turtle)

P.S. You've got nothing to lose with clean touch points.

 

Wishing you good luck. Not sure why someone engineered your 2015 like that. Difficult to troubleshoot and expensive to repair?

 

Not generally expensive to repair, but definitely difficult to reach most things without disassembly. This is the only part I've had real difficulty with, I get that only the newer bikes don't have starter relays but I still don't get why I can't find anyone else having these issues.