ABS Light, No rear brake

VPS1

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#21
Thanks for all the help with this, as usual I have learned a lot. Last night I was able to do the ABS cycle correctly and it does pulse the handbrake and brake lever, did it many times. I bled the rear brakes, flushed them with half a bottle of fluid! Cycled the ABS probably 10 times as I bled, filled, bled, filled. The old fluid was not very dark but it was think and nasty, so my bad. No residue or sludge in the reservoir. Got it all flushed and went for a ride. EVERYTHING is fine. Normal front and rear brake, normal unafied brakes, no stiff rear pedal no ABS light! Rode it for about half an hour, pushed it till ABS came on many times. Really seems 100%. Time will tell but I may have dodged that bullet. I need more fluid so I can do the fronts, then the rears one more time. Thanks everyone, really appreciate all the help and comments.
 
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#22
Well, the brake problem is still happening. I have read a bunch of posts about rear brake issues and it seems most involve air getting into the system and the pedal going soft, no brakes. My issue is that the rear pedal get stuck, when it is stuck the ABS ligt comes on when I use the front brake while moving. I know the unafied brakes use the ABS module to activate the rear brake. I mostly do not use the rear brake pedal, maybe that contributed this. The bike is in for the harness recall and to get this looked at. Feeling expensive at this point. I will update as I hear whats up.
 
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#24
Will the pedal lift up by hand when it is jammed or is it jammed in the up position? If the brake is jammed on and the pedal is rock hard in the up position it has to be trapped pressure caused by a sticking solenoid valve in the ABS unit when the UBS is activated.
There is separation,inlet, shuttle and outlet valves on the rear brake.

The ABS unit looks at both front and back master cylinder and caliper pressures during braking and will fault if it can’t see the pressures it is trying to maintain. Hopefully the dealer will do the fault code reading and narrow it down.

It would be interesting to open the bleed port when this has happened and see if it’s trapped pressure. If there was no pressure it would be the caliper or stuck pads.
 
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#25
Thanks for the comments Mike. It’s throwing codes that are exactly as you mention, unexpected pressures in rear master and caliper. I think 73 and 74 or 74 and 75?? Pedal is tight in upper position and can be pressed hard to clear, very hard. Looking like an abs unit fault. Brought on by activating unified brakes. They are still troubleshooting and said they would know soon. Seems like they are giving the diagnostics a good go before suggesting the whole unit be replaced. Feeling expensive. I will state I do use unified brake most of the time, very rarely used just the rear, wonder if that caused at least some of this?


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#26
Thanks for the comments Mike. It’s throwing codes that are exactly as you mention, unexpected pressures in rear master and caliper. I think 73 and 74 or 74 and 75?? Pedal is tight in upper position and can be pressed hard to clear, very hard. Looking like an abs unit fault. Brought on by activating unified brakes. They are still troubleshooting and said they would know soon. Seems like they are giving the diagnostics a good go before suggesting the whole unit be replaced. Feeling expensive. I will state I do use unified brake most of the time, very rarely used just the rear, wonder if that caused at least some of this?


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It does sound like one of the valves isn’t releasing pressure and whether it’s the brake ECU or the valves is the $1000 question.
If you want to understand the system better have a look at the thread “What the inside of a bad ABS unit looks like” that I wrote this morning in brakes.
Hope it works out for you.
 
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#27
I read that post of yours minutes after you posted it! Should hear something tomorrow either way. Pretty sure this is about to get expensive. This bike has been 100% for all these miles, just had first valve check done at 34,000 and still in spec. No other issues, so I will get a new pump if thats the issue. The bike is so set up for me, been looking at adding cruise.
 
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#28
Just heard from Service advisor, they have been riding it off and on yesterday and today with no faults, no hard pedal, no ABS light, no codes. He is skeptical but Yamaha advised him that a hard pedal is uncommon (as compared to soft pedal/air) and usually something foreign in the fluid causing a clog. They are thinking it was bled out in one of the thousands of gallons they bled through it all! LOL. Service advisor has made himself very knowledgeable about this bike and the ABS as they have worked through this, I am impressed. He thinks it will come back, sooner than later and is thinking it will in the end be the ABS pump . I will get it in the AM and see what happens. They get 1200 for the pump and 500 install, so 1700 is a big deal. I am willing to ride a bit and see.
 
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