2005 k1200lt. BMW logo on the front caliper so integral ABS system.

I recently have the ABS light and General warning light come on in an alternating pattern once a second. According to the chart in my manual, this indicates the brake fluid level is low. I've checked the front reservoir by turning the handle so the reservoir itself is parallel/flat to the ground and its fine. Checking the back reservoir is a little more tricky as the plastic is hard to see through but the level shows in the middle between min and max. So the fluid levels look fine but my manual gives no other option than fluid is low somewhere. I don't have a code reader so I don't have any more details than that.

Possibly defective fluid level sensor? I didn't see in my manual (Clymer) anything about checking or repairing a brake fluid level sensor.

Any thoughts?
Any suggestions on best sources for a code reader?

Before you go with a GS911 code reader (or the dealer), you need to check the "proper" reservoirs.

On K1200LT of last generation (2005-2009) the only reservoirs that are monitored by the ABS system are located on top of the ABS modulator. Only these have electric circuits with floats (2 of them) that will trigger the fault that you see. Assuming that what you saw is low speed (1 per second) alternating flashing of both Warnings. IMPORTANT to note that if either float are disconnected -OR- a wire damaged (these wires are near the cap reservoir) the system will trigger the same fault (thinking the fluid is low).

See attached photo for location of these 2 reservoirs on top of the ABS unit (circle in Yellow to point to correct location). Of course, yours will have small black plastic cap that you can remove using a 19mm wrench and you should also have vent hose attached to it. Normally, when the last bleed was done properly, the low level is not reached until the brake pads are fully worn. In the same logic, the MAX level should only be topped with brand new brake pads.

If you put too much fluid (to MAX level with brake pads worn to min level) , whenever the caliper(s) pistons are compressed (like removing the wheel) the fluid will overflow to the ground by the small hoses attached to cap.

ALTHOUGH the other reservoirs at handlebar and above footpeg are NOT monitored directly by the ABS system, I think you should still make a habit to check these for proper level at yearly interval (a minimum in my opinion).

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The way these reservoirs are set up, when they get low it usually means your pads are just about worn out.

Thanks for the input. Brake pads are relatively new and the brake system was flushed at the dealer about 1,000 miles ago.

My Clymer manual doesn't help at all on the ABS unit. It simply says to take it to a dealer. I'm not clear on the routing of the brake system, however, I assume the upper reservoirs (on the handle and under the seat) feed the ABS unit and the reservoir you are referring to. So if the upper reservoir is full, there is no reason that the ABS reservoir is low unless there was some kind of blockage (I feel no degradation in braking performance at all by the way). So I'm assuming that the most likely culprit is a faulty float switch/wiring on the ABS unit. Does anyone have any details on the wiring and location of the level sensor in the ABS unit? Otherwise, I'm not sure its worth tearing down to get to the ABS unit if I don't have any guidance on how to repair it. I guess I'm stuck taking it into the shop or winging it on my own.

did you check the reservoirs at the abs as suggested by sailor? assuming these braking systems are like others is a mistake, they they are not it may be a very simple fix of a top up.

I had this happen to mine about a year ago and what I found was the rear reservoir under the seat was low. I blead the rear circuit and that fixed the problem. At the next opportunity I replaced all the lines with Spieglers . What I noticed on mine was that fluid would occasionally be found running down the outside of the transfer tube between the rear reservoir and the master cylinder at the foot pedal. I found that this was coming from the filler cap which I think wasn't seated properly, it's a little awkward to access.

The exterior reservoirs do not feed the ABS reservoirs. You have to access the ABS unit and fill them.

I have not inspected the ABS reservoir yet, I haven't had time. I'm still trying to understand the design of the system so I can fix the problem. My understanding is that the integral ABS system should never show low brake fluid levels not matter what the pad wear is. So simply topping off the ABS unit isn't fixing the issue. In what scenario could the upper reservoir be full and the ABS reservoir not full? If it wasn't flushed properly at the dealer 1,000 miles ago, I assume it would have shown as problem before now.

I will re-read the manual again to see if there is any kind of schematic that shows the flow of fluid between the upper reservoir, master cylinder and abs unit. For some reason I didn't see that kind of detail for the integrated ABS system.

Also, on the way home last night the lights went to the cycle of alternating 4 times a second. So it's parked until I figure out what is going on.

As mentioned above, the fluid in the ABS unit does not correlate to the hand or foot brake master cylinders. The ABS unit is filled separately at the two reservoirs on the module itself where the overflow tube is attached to. Use an Allen key to remove the two caps and once removed you will see a white line, actually part of the screen filter that can be pulled out for siphoning the fluid, where the fluid level should be at. If you do not see fluid at this line then the sensors will pick that up through the warning lights.

I would check the ABS reservoir fluid level first but it now sounds like you may have a different problem if you are getting the 4 times a second flash coupled with a steady °!° warning light. If you have travelled 1,000 miles after the system was flushed, then your issue is to determine why the fluid level is now low otherwise you would have seen warning lights at the time of the flush.

The fluid level will go down with the wearing of the pads or if there is a leak somewhere in the system or if indeed the module itself has failed allowing the fluid to escape into other sections of the module in which case it is leaking fluid from within and you will not see signs of fluid leaking until you dismantle the module.

HTH

Maybe this will help you under stand the brake system a bit better. If the pads wear the pistons move out and that space is filled with brake fluid that has to come from somewhere. The early bikes would give you the wig wag lights with just a teaspoon of fluid gone from the reservoir. On the 05 and up the reservoirs ON the ABS supply the fluid to the calipers and are bigger with the floats set to trigger the wig wag when the pads are worn out.

During a flush the pistons of the calipers are pushed in all the way (if done properly) and the fluid level set to the top of the reservoir. Then the pistons are pushed back out to the pads and the fluid level drops, when it gets low enough to trigger the wig wag the pads are worn.

The fluid in the control circuits just push pistons in the ABS and the fluid never mixes with the wheel circuits.

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Thank you for the schematic and more detailed explanation. I understand now how they are two separate circuits. This project will have to sit for a while until I can find time to tear it down.