Help! No rear brake! FIXED!!!

[granbo]

I was in the process of flushing and bleeding the ABS. I have preformed this service twice before over the past 3 years without issue. But this time when servicing the rear wheel circuit I turned on the ignition to allow the ABS to initialize but when I applied pressure on the footbrake pedal the pump failed to operate. I can hear a distinct click from the ABS control module but no wining. The front wheel circuit bleed went uneventful.
Some past history...Before I started the ABS service the general warning light was on and the ABS warning light was off and changing out the tail light failed to remedy the problem.
Also, the rear brake light functions at the hand but not at the foot brake.
Presently, the general warning light is on and the ABS warning light is flashing @ 4hz.
The battery is an Odyssey and shows 13.30 v.
I reassembled the bike and took it for a careful test ride. The rear brakes clearly are not functioning but the front brakes are. Any ideas????????
2002 r1150r 40k miles

[iowabeakster]

I hope Sweatmark sees this post. He recently removed the ABS system and has a better understading of the electrical circuits than I. But I think you are looking at an electrical problem (no light with the rear brake).

My only guesses:
1. the switch at the rear brake pedal is non-functional
2. the small plug for the rear circuit on the ABS module is unplugged
3. the gigantic plug on the ABS module is not making contact with one of the pins (I bent one reinstalling the plug one time, easily fixed, just straighen it out)
4. broken wire somwhere
5. ABS module has gone kablooey

Was the rear brake working before the service?

[granbo]

Yes, the rear brake was working before I started the bleed. It started to fail after installing a new tail light. I test it a couple of time by placing pressure on the foot pedal. At first it worked and then nothing. Could it be a brake light switch?
And does the switch control both the brake light and activated the servo?
thanks

[sweatmark]

Yes, the rear brake was working before I started the bleed. It started to fail after installing a new tail light. I test it a couple of time by placing pressure on the foot pedal. At first it worked and then nothing. Could it be a brake light switch?
And does the switch control both the brake light and activated the servo?

Well, I'll confess to no particular expertise with the iABS system, but will throw a couple ideas out there:

The iABS has fluid level sensors on each circuit (front/back), so is it possible that your rear brake pedal test could have pumped brake fluid back to the rear caliper and lowered fluid level below the required minimum? Guessing that a low level would trip the ABS warning lamp and caused the ABS computer to shut down the rear brake servo pump.

If the fluid level sensor itself (or its connector) got whacked, then the same result would be expected. Unknown/untested if the fluid level switches are normally open or closed circuits.

Another idea: the iABS brake switches are unconventional, insofar as they are normally closed (connected) until switch is activated, then the circuit is broken. As suggested above, a broken wire or faulty brake switch might cause a logic fault in the ABS computer, shutting down the rear brake servo.

I doubt that the problem's in the big ABS wiring connector, as it's beefy and kryptonite-strong. Is this connector normally detached to perform ABS fluid service?

A possible troubleshooting strategy (after confirming that the fluid level is OK in rear circuit) would be to check continuity of the rear brake switch near the ABs wiring connector. If you can tap into the respective wires (not an easy task), then a faulty switch and/or wiring would reveal itself. I don't know the iABS logic, or whether the brake switch's operation is linked directly to servo actuation, which seems doubtful... I wouldn't want braking performance of man & machine hanging by the slender thread of a small switch explosed to the elements.

Finally, it's possible that the ABS rear circuit pump is kaputt. There's a diagnostic capability for the iABS computer that your dealer can read, though certainly for a price.

[iowabeakster]

As far as the light goes, yes, it defintiely could be a bad switch. That is where I would start. That would explain why you had a problem with the light before the service. First I would test the switch, and then general continutity of the circuit(check for broken wire, or disconnection) with a volt meter.

Does the electrical switch control the servo operation? I don't think so (this is an assumption, you know what they say about assumptions). I think it is actuated by fluid pressure. I believe that I can get my servo to run by just the slightest touch of the pedal (or lever)...even before the switch clicks the light on. I will try when I get home.

I just had another thought (scary). What is the level of fluid, in the rear wheel ciruit of the ABS module? If it is too high, or too low, it will trigger an error.

Did you flush the control circuits too? Before or after the wheel circuit difficulty?


Edit- I started to respond, then did some research, and Sweatmark responded in the meantime. So much of the above just repeats what he said

Sweatmark asked,

Is this connector normally detached to perform ABS fluid service?

I don't know if it is normal, but I sure detatch it. I find it impossible to get to those six bleed nipples without removing it. This is how I managed to bend a pin.

[granbo]

The sequence of events before the rear brake failure were as follow:
I was returning from the mountains when I was caught in a sudden rain storm lasting about 15 minutes. Immediately I noticed that the general warning light was on. The ABS light was not on. Rear brake appeared to be functioning. When I return home I checked the fault table in the riders manual. It stated tail light/brake light inoperative. A new bulb did not renew the tail light. Also, still had the general warning light. Again, brake light but no tail light.
After testing the brake light several times I noticed that the brake light would function at the handle bar but not the pedal brake. I decide to bleed both front and rear wheel and control circuits. Everything went fine until I blead the rear wheel circuit. Suddenly the ABS warning light went crazy. I probably introduced air into the system because the servo failed to spool up. After talking to several BMW mechanics the general consensus was that foot pedal brake switch is part of the ABS system. If your brake light switch is not functioning then your ABS will not function. Apparently the rear brake switch communicates with the ABS control unit. Apparently Sweatmark is correct in that the brake switch operation is linked to the servo actuation. Page 783 in the Clymer outlines this in the wiring diagram. If it’s true that a brake switch can cause ABS failure then I’m thinking dumb design. Doesn’t make sense…
The plan is to R&R the rear brake switch. Maybe it was gunked from the mud and rain.
Don’t know… I may have two separate issues…thanks for the help…I’ll keep you posted.

[iowabeakster]

I learned something new. I played with the bike today. But I forgot after work yesterday and only had few minutes before taking off to work.

First I tried to barely activate the brakes. The servo and the lights seemd to operate as one, I could not get the servo to run without the brake light lighting.

I pulled out the switch in the handlebar. (seemed easier than the rear switch because I didn't have to bend over so much)

1. With the switch open (no current flowing), I turn on the key . The bike does not complete its self-diagnosis. (This is the same as starting up with your brakes applied). Error Result: General light on, ABS light flashes at 4 hz.

2. With the bike still on, I close the switch (current starts flowing). The bike finishes the self-diagnosis. Result is normal operation: General light off, ABS light flashes at 1 hz. It is ready for the pull-away test of the wheel sensors. Once the start-up test has been passed, the lights and servo operate normally (squeezing the lever), irregardless of the switch.

3. So I turn the bike off, and open the switch again. Turn the bike on, and once again, an error in the self-diagnosis. This time I squeeze the lever (with the bike still showing error). Servos AND brake light activate!! The brake light Will illuminate with the switch open, as does the servo function. The servo AND the brake lights are actuated by fluid pressure!

***What I found was that the FRONT switch is a redundant system to operate the brake light only if the servo system fails. The front switch does not actuate the servo or the brake light under "normal" operation. The front switch is tested at start-up (passing current, verifying it's closed status), but otherwise have no function in the operation of anything (unless the ABS craps out while riding and then it operates the brake light). But, turning the key on with the switch open will cause error. The brake light and servo should operate even with the error flashing.

I will adjust the bolt which operates the rear switch tonight. I will back it down so that the switch is open, and see if the servo and brake light operate with the error flashing, just like the front did.

edit--The mechanics were right, the switch is needed to operate the rear servo, but not on the front. I corrected my findings above as it only applied to the front switch. On the rear switch, the bolt would not back down enough, so I disconnected at the wiring harness.

[iowabeakster]

If it’s true that a brake switch can cause ABS failure then I’m thinking dumb design. Doesn’t make sense…

Further experimentation says...dumb design.

1. I disconnected the rear switch and turn the key on:

general warning light: off
abs warning light: 4 hz
brake/tail light: BRAKE light ON (continuous)
depress the pedal: NO SERVO
front brakes: servo OK

2. connect the rear switch

all systems normal

I really didn't think that the engineers would leave the ABS system opeation vulnerable with that exposed switch. WRONG. The rear operates completely different than the front. At least the front brake operation isn't dependent on exposed switches, as it is operated by fluid pressure. Man this is a strange system.

There is an handy harness for disconnection of the rear switch that is zip-tied to the frame. It is in between the fuse box and the charcoal cannister valve. It would be an ideal place to test the switch and wiring.

[granbo]

Well I decided to take it to the dealer. Brown Motor Works BMW in Pomona checked for fault codes. Diagnostic testing found that " checked harness to ABS module one of the wires are grounded and that additional diagnosis would involve opening the wiring harness to find which wire is causing the problem and where...recommend replacing the electrical harness."
Total cost $2300. The harness is $1700. Labor is $600. Hefty bill for a bike that bluebooks at $4700.
The last part of the work order reads..."customer declines repairs at this time." The cost for the testing was a reasonable $108.90. The folks at Brown Motors were very courteous. I'm not slaming them...readers this is the "cost" of owing a BMW motorcycle.
Presently the bike has the following issues:
1. No brake light at the foot pedal, (the brake light does however function at the hand.)
2. No tail light except when the key is turned counter clock wise in the parking position.
3. No ABS. The front brakes seem to work normal...the rear takes a heavy foot to slow down.
The foot pedal brake switch is intact. The problem according to the mechanic is somewhere aft of the ABS module.
The bike is functional and I'm still riding but I hate the idea that the machine is sick. Likely only one wire is the culprit.
Going to tear into it tonight. If you have any ideas please post them here...thanks...

[sweatmark]

The foot pedal brake switch is intact. The problem according to the mechanic is somewhere aft of the ABS module.
The bike is functional and I'm still riding but I hate the idea that the machine is sick. Likely only one wire is the culprit.
Going to tear into it tonight. If you have any ideas please post them here.

OK, I've already tried to talk you into removing that crazy ABS system, but since you insist on keeping it...

I would check continuity of the rear brake switch wiring, from switch to ABS computer. Do this by separating the ABS wiring harness connector at the ABS module and testing the two contacts that loop through the rear brake switch. You will need a sewing needle (well, two of them) to make connection into the female sockets in the big AMP connector - the pins you will find on the ABS module side are impossibly small. Based on the info stated above, an open circuit in that rear switch would produce your symptoms.

So, if you isolate the rear brake switch open circuit within the ABS harness, then screw the idea of all that money to replace harness, etc.; instead, just dig into the harness below the AMP connector, cut the rear brake switch wires, connect the ABS-side ends to new wires you run along right side of bike subframe to connect to the rear brake switch (which you confirmed was operational), confirm continuity for the circuit at the AMP connector, test system, cheers.

If the entire rear brake switch circuit proves OK, then it's your call what to do next... rip the ABS out!

[iowabeakster]

I agree with what Sweatmark says. However, if you would find the wiring broken (we are already assuming this because the BMW guys say the ABS module is OK and they were going to seriously overcharge you for a harness), you don't know where the break is.

To narrow it down, find the disconnection plug between the rear switch and the ABS module. It is wire tied to frame between the fuse box and the charcoal cannister valve. It is just a small standard two wire junction connector. You will need to remove the seat and plastic side panel on the right side of the bike first. Clip the wire tie. Disconnect the plug. Make a wire jumper to connect the contacts on the side of the plug that is attached to the ABS module. Turn on bike.

If the ABS system passes it's test normal...you know that the broken wire is aft of that point. Easy fix, replace wire.

If the ABS system does not work...the problem is forward of the plug and will be more tedious and you may need to tear that big harness apart to find the break.

[granbo]

iowabeakster said...
"Make a wire jumper to connect the contacts on the side of the plug that is attached to the ABS module"

I understand the concept and I have found the disconnection plug between the rear switch however exactly where on the ABS module do I connect the wire jumper? thanks...

Sweatmark thanks for the helpful info...I've read the ABSectomy several times trying to absorb it. The pictures on photobucket are not clear. They keep coming up miniature size. I'm also not sure what parts to order. I'll keep trying.

[iowabeakster]

Don't jumper back to the ABS. Just jumper between the two contacts (+ and -) on same plug. I was envisioning a jumper of less than two inches. Making a simple closure of that circuit. All this is doing is bypassing the foot switch and the length of wire to the switch.

[sweatmark]

granbo-

Can send you original pics from ABS removal if needed. Most pics were shrunk down for posting, and originals weren't that great to begin with, having been shot with either BlackBerry or an old Canon "garage camera".

Beakster's recommendation is the most straightforward 1st step. I thought you had already confirmed that the rear brake switch and its wire section (from foot switch up to that first connector) were OK, and if that section proves good, then my suggestion is to confirm that the entire rear brake switch circuit from ABS module (wire from ABS to brake switch and back again) passes continuity check.

Based on the results of that continuity check, you will define your options to fix.

[granbo]

Victory!!!!! Had to remove the rear wheel and partial fender to access the inferior portion of the fuse box. I swear a jolt of terror ripped thru my head staring at what seemed to be 10 thousand wires all in neat bundles. I’m thinking I must be insane only a BMW neurologist or a crazy person would dare touch these wires! So with perspiration running off my forehead and trembling hands I begin to unbundled and separated all the wires…taking notes, hyperventilating and feeling stupid. After about 15minutes I noticed two strange wires that were somehow semi-fused together. After separating the wires I noticed several bare places on one of the wires. Maybe? Turn the key and like magic the problem’s resolved. Apparently the mating wires caused an electrical conflict. Remember BMW wanted $2300 to fix the problem.
I must say my feeling of self-satisfaction and reliance was as good as it gets.
The moral of this story is….Just go for it!!…chances are the results will be positive.
Thanks to beakster and sweatmark helpful advice.

[bikermeow]

Hiya, I had just stripped all visible wiring tape off my wires, cleaned off the sticky gunk and checked (or try to check) all of them by feel and flex. One broke earth wire was fixed, and bundles re-wrapped. Flex ties back on (not too tight) and feeling kinda happy that I did it.

With heat and the tropical climate that I am in, I reckon that these wires need checking.

[iowabeakster]

granbo,

$2300 well earned!!! congratulations!!!

Thanks for posting your problem. I learned a lot about this crazy system that I previously did not know. Invaluable to me also.

Most of the time, if an ABS question pops up, the answer is, "bend over for the dealer." I am happy to see this one did not require that.

[sweatmark]

granbo - high5; so you don't need the ABS-ectomy info.... yet!

[bikermeow]

Yo, sweatmark, did you have to substitute one of the relays to a non-ABS one such that the front brakes will trigger the brake light? If so would like a part number for the relay.

Cheers

[staape]

Hi,

I found this conversation when I tried to find solution for the similar problem in my R1150R. I was a dealer, and they made yesterday test and it seems that there is ABS module is OK and the fault is electrical. Also back brake light switch has been changed, so it is new. When you found the fault from wiring, is there some specific riskplace where I should try to find damage. I would be grateful for answers.