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Thread: iABS Phantom Activation of Brake Light and Servo

  1. #1
    Registered User
    Join Date
    Mar 2007
    Ambler, PA

    iABS Phantom Activation of Brake Light and Servo

    R1150RT, '02, 176k miles

    The brake light and ABS servos come on spontaneously, with no pattern, intermittently, getting worse over a year.
    They stay ON until I turn off the key.
    May occur at any time like riding at speed or immediately after key-on. As of a few months ago it has been repeating so regularly that I finally have a chance to diagnose it, and have been investigating many weeks.

    Note that this problem does not cause any braking at the calipers, which only responds to the proportional squeeze on the brake lever, which is 0.

    Also note that no ABS fault is shown via the GEN or ABS lights.
    The brakes continue to work fine, with or without the problem presenting.

    This problem may be related to Thread "ABS Troubleshooting" started by dagear. in both, the servos stay on until key-off. But in his case the front brake lever will not activate the servo, while the problem can be initiated by tapping the rear brake, (and he asserts the foot lever is not sticking down)

    My standard test routine: key-on, wait for ABS initialization completion (ends with ABS flash at 1Hz awaiting driveaway test), then 3 seconds later the servo and brake light come on, about 1/3 of the time. They stay actuated until key-off.

    No amount of wiggle testing, hammer tapping, PC board wiggling has the slightest influence on starting or stopping the problem.

    I have bled both wheel and control fluid circuits, and removed one pressure relief valve, hoping to find crud. But fluid was clean, like new everywhere. The valve plunger worked like new.

    I do have original rubber brake lines, but I exclude these as culprits since I see good fluid pressure readings and find no sign of crud in brake fluid. Also I can't conceive of any logical connection between collapsed or damaged brake lines with my stuck-servo problem. I know I am on thin ice here, many insist on replacing these first.

    I have excluded the brake switches and all harness wiring as culprits, by disconnecting the ABS connector and hot wiring the ABS module, where I have split open the electronic part to access the PC board . I jumpered the brake circuits and fluid level circuits as closed circuit, connected power and ground, etc. Result: the problem still occurs, randomly, with about the same frequency.

    Throughout testing, battery voltage never drops below 12.2V
    Removing the ABS Relay and Load Relief Relay have no effect on stopping or starting the problem (I leave Load Relief Relay out during long testing to keep headlight off).

    My newly acquired GS-911 shows the following interesting results:
    -faulty rear brake switch (even when short circuited at the module). But it should be noted that other faults in wheel sensors, fluid pressures, servo motors, seem to come and go rather at random, that brake switch fault is just slightly more evident.

    -uniform and plausible fluid pressure readings from 19 to 90 Bar in 4 places during brake squeeze. I infer that the 4 pressure transducers are working and that the processor successfully converts analog MV to Bar digitally and reports it.

    -Surprisingly, the problem never occurs if the GS-911 is connected. Similarly, if I connect GS-911 after problem is occurring, the problem clears (servos off) at the instant where the GS-911 displays the data on the laptop screen, whether "ABS Status" or "Fault Code" data. Of course I am hoping to see an interesting fault in this case. Usually there are no 'present' faults, but occasionally (1 in 10 times) it shows defective servo motor or rear brake switch, without any pattern.

    -ABS ROM code checksum = 78, per ECU data. From this I infer that a software corruption could be easily reported, but it is not, therefore the software should be good. (but perhaps only the dealer could run a true software test)

    In addition to GS-911 plausible reports of fluid pressure, I have probed the electrical outputs of the 4 pressure transducers and found plausible voltage range over a brake squeeze.

    I believe the ABS processor will actuate servo and brake light for either a brake switch interruption or a control fluid circuit pressure rise (per my testing). Now I am close to excluding the fluid pressure as culprit, due to clean fluid and plausible transducer output.

    Therefore I am left with only one theory: an intermittent interruption of the brake circuit signals on the ABS PC board. The top of this board looks pristine in every respect, no sign of moisture or corrosion. I may try to pry the board out of the aluminum case (risking damage at the seal) to examine the underside. Tracing the circuits and looking for bad solder seems rather hopeless, but it's the only thing left.

    Other recourse?
    -I can't justify dealer repair due to age and condition of my R1150RT at 176k miles. They would begin with new ABS module ($2400 or so) and go from there.
    -Module Masters still is 'on the verge' of being able to rebuild iABS
    -eBay occasionally shows an iABS module, at around $1000.

    I can't find any record of this problem occurring to anyone else.
    Doug Raymond,
    R1150RT '02, R1200GSA '11

  2. #2
    Registered User Blacque Jacque Shellacque's Avatar
    Join Date
    Nov 2005
    Pickering, Ontario
    Judging from the symptoms your listed, it would seem iABS controller is fried. When the servor failed on my RS, I picked up 2 used units that supposedly worked. The first one never made it past the self test, it whined continuously. The second one passed the self test and whined continuously after applying the brakes. It's difficult to find a used good working unit. I ended up biting the bullet and purchased a new one from a dealer and installed it myself. In my opinion the units are self contained. With the exception of the brake switches, they either work or they don't. When computers and controllers fail, depending on how or which component failed, the symptoms can be quite wonky and variable.

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