ABS is erratic

[HYCLE]

The ABS will activate when the front and rear wheel speed sensors are not sending the same speed signal...

:devil: Does this mean that your ABS light comes on every time you wheelie? (Yes, if you ride on one wheel long enough for there to become a significant rotation difference between the front and rear wheel. Go try it.) By design it *should* be impossible for either wheel to have an incorrect ABS frequency for a given speed. The conditions where the ABS is commanded to activate is is generally more complex than just wheel rotation speed.

Do you get the ABS like feel when only using the front brake? Do you feel the ABS sensation when lightly using the back brake only? Seriously, do try this, read the next line and see why.

About 24k miles ago my FJR started making a high speed ABS like pulsing too. It coincided with changing from Pirelli tires to PR2s and it gets worse as the front tire wears. Dunno about other brands of tires but I would suspect tires long before the ABS.

Guess I forgot to mention all the infomation needed for the ABS to activate. Like the ignition must be on, the brakes must be applied, the ABS light must be out and some systems are programed to see that the wheel is slowing faster than possible for a safe stop on that vehicle and lock up is possible.

What else did I forget to mention.....you would need to ask the engineer that designed and tested that particular unit with that version of software.

As to addressing the wheel speed sensor differance... if one sensor has a wide air gap and will not generate a signal at low speeds, this can cause the controller to think one wheel is stopped, when in fact it is moving at the correct speed. Metal fillings stuck to the magnetic wheel speed sensor will also degrade the output signal

sometimes to the point of no signal at slow speed.

We had an employees Acura come in with a code set for the left wheel speed sensor, I recommended they test the output and resistance of the sensor. They did not want to put the car on the rack for testing and would check it out at home. The wheel bearing failed on the way home and it was the cause of the bad sensor reading. Couldn't diagnose that one without looking at the big picture.

Hope your finding your problem and it is just a minor repair.

 

[ionbeam]

Guess I forgot to mention all the infomation needed for the ABS to activate. Like the ignition must be on, the brakes must be applied, the ABS light must be out and some systems are programed to see that the wheel is slowing faster than possible for a safe stop...What else did I forget to mention...

Well, the fundamental activation point for ABS is the slip angle; the wheel to wheel to speed is secondary to the primary down the road trigger point.

 

[TechJunkie]

I want a refund on my Advanced MSF course since they had me practicing dangerous maneuvers such as trying to stop as fast as I could causing the ABS to activiate. Shame on them!

I must admit the instructors were both impressed with my FJRs brakes. They both commented on how quickly such a heavy bike could stop compared to many of the other lighter bikes without ABS. One rode an ST1300 and he kept talking to me about my FJR and what I liked about it.

 

[azitlies]

Guess I forgot to mention all the infomation needed for the ABS to activate. Like the ignition must be on, the brakes must be applied, the ABS light must be out and some systems are programed to see that the wheel is slowing faster than possible for a safe stop...What else did I forget to mention...

Well, the fundamental activation point for ABS is the slip angle; the wheel to wheel to speed is secondary to the primary down the road trigger point.

That's interesting information. Another aspect of this is the physical capability of the tires right?

I mean, to use an extreme example, crappy hard tires like something an OEM might use vs high performance track tires? The traction difference between these would be extreme, but in this example, doesn't the "abs system" still calculate things the same way? Regardless of the fact the track tires still have a lot of traction left?

IMHO, that's the reason ABS has it's detractors, it has to be 'programmed' for the least common denominator (crappiest tires).

 

[RaYzerman19]

My '07 does this, but mostly when I'm coming off the freeway as I am *releasing* the brakes from fairly hard to fairly gentle. I feel the same servo-buzz in the front lever that you feel when testing the ABS, or when it's firing for real. I don't seem to feel any change in my braking speed over what I'm doing. It's very repeatable.

EDIT: to be clear, I don't think it's an issue, maybe just a corner-case in the programming for the ABS unit.

I get this occasionally too, and am happy to know that buzz tells the ABS system is working. Normal to me now. But for those who aren't familiar with ABS sytems, the default in the unlikely event of an ABS failure is to become a non-ABS system, not a brake system "failure" per se.

Are you *sure* it's the ABS activating? That just doesn't seem right.

Admittedly, it is a bit odd. But it is ABS pump activation of some kind. In my case I can be coasting slow up to a stop, and just before I stop, front brakes on only, the lever will pulsate/buzz slightly for a couple of seconds just before full stop. No real reason why it should, since the front wasn't about to lose traction. But it's only once in a while, and I chalked it up to thinking it was a good thing I know the ABS system is working. OTOH, I have hit the brakes hard at speed, downhill, rear tire (Exalto) chirped a bit as it skipped a bit on uneven pavement, and I did not feel any pulsing in the brake system. In that case, ABS must have been working or I would have skidded the rear, but I didn't feel any buzzing.

 

[HYCLE]

Guess I forgot to mention all the infomation needed for the ABS to activate. Like the ignition must be on, the brakes must be applied, the ABS light must be out and some systems are programed to see that the wheel is slowing faster than possible for a safe stop...What else did I forget to mention...

Well, the fundamental activation point for ABS is the slip angle; the wheel to wheel to speed is secondary to the primary down the road trigger point.

I need some enlightenment. If all I have for sensors are two wheel speed sensors how does the controller know chassis speed? Does the FJR have inertia sensors? Or are we talking the theoretical chassis speed, based on the faster of the wheel speed sensors?

I don't have a factory manual to check the wiring diagram for inputs to the module.

 

[HYCLE]

Guess I forgot to mention all the infomation needed for the ABS to activate. Like the ignition must be on, the brakes must be applied, the ABS light must be out and some systems are programed to see that the wheel is slowing faster than possible for a safe stop...What else did I forget to mention...

Well, the fundamental activation point for ABS is the slip angle; the wheel to wheel to speed is secondary to the primary down the road trigger point.

I need some enlightenment. If all I have for sensors are two wheel speed sensors how does the controller know chassis speed? Does the FJR have inertia sensors? Or are we talking the theoretical chassis speed, based on the faster of the wheel speed sensors?

I don't have a factory manual to check the wiring diagram for inputs to the module.

Here is a great link to ABS operation and the different possible inputs for chassis speed. Do we know which inputs are available on the FJR? Do we have Deceleration Sensors or do we just compare wheel speeds?

Toyota ABS Training

 

[LAF]

I find this fascinating.

First thing I did was find some gravel and kick the ABS in. I wanted to know what it felt like.

My first car with ABS is my current car and I did the same thing try them out. As it was my first experience with ABS and it scared the crap out of me. Such pulsing and carrying on.

I believe the FJR just uses wheel speed sensors. I did lock mine up on the way to get my brakes flushed to move fluid through it.

If you guys are experiencing ABS action other then clamped down on both front and rear brakes, something is wrong for sure. The person who said it is repeatable in one sweeper off a highway the only thing I can think of is you have wheel hop from a light suspension?

Regardless you guys need to check it out. Maybe your magnet on you hub is messed up, scraped up from a sloppy tire change? Someone got a magnetic tool on or near it, wire pinched, sensor messed up, I always put a light coat of grease on my sensor that goes into the hub, something is wrong for sure if you have intermittent ABS kick in with light brake pressure.

You guys who have never tried locking up you brakes to kick in ABS, you will regret that if it really comes down to using them, as you will have so much going on, and then it kicking in will really add to you 2 seconds of horror.

 

[wfooshee]

Every car with ABS I've ever had, one of the first things I did was find a dirt road and hit the brakes hard. Then I'd do it on pavement. I wanted to know what it would do, whether the pedal kicked or didn't kick, what it sounded like, did any pumps start running, and whether it would stop working if activated long enough or repeatedly enough.

I'd say I've done the same with every bike with ABS I've had, which would be true.... but I've never had a bike with ABS.

 

[ionbeam]

...Do we have Deceleration Sensors or do we just compare wheel speeds?

The FJR ABS ECU uses wheel speed and chassis speed then does the math. There are no other accelerometers or sensor inputs.

 

[HYCLE]

...Do we have Deceleration Sensors or do we just compare wheel speeds?

The FJR ABS ECU uses wheel speed and chassis speed then does the math. There are no other accelerometers or sensor inputs.

Can you explain how it determines chassis speed without using the wheel speed sensors or another input? Is it recording the live,average, road speed and then comparing that to a wheel decelerating to a speed below 87%.

I am trying to get a better understanding of the logic used on a system with only wheel speed sensor inputs.

For example: I explain to my students that a 1990 Chevy truck,with rear wheel antilock brakes, uses only the speedo sensor on the output shaft of the transmission. I assume the logic is, if the speed signal slows faster than theoreticly possible, for that vehicle in stock form,the rear brake pressure is reduced.

This causes the vehicle to have a greater stopping distance but allows you to steer and possibly avoid a collision. With better brakes and tires you may improve the vehicles stopping distance and this would be cancelled by the set program in the unit.The system will not let you stop quicker than it was programmed to allow.

Being able to steer allows you some choice where you will eventually crash.

 

[ionbeam]

I haven't found anything that explains all the details of the FJR ABS system. I do have a Technical Orientation Guide with details for a Gen I that was available to dealers which explains things that the FSM doesn't go into, but haven't found one for the ABS. One of the guys that I know through my car club was the GM engineer tasked with developing ABS systems for GM's non-commercial vehicles. I learned a lot of technical things from him, including the first time that I heard about 'slip angle' in his crew's vernacular and 'slip ratio' in Yamaha speak.

The FSM says that the "slip ratio is the value that shows the rate of wheel slippage and is defined by the following formula":

Slip ratio = ((chassis speed - wheel speed)/chassis speed) * 100 (%)

0%: There is no slipping between the wheel and the road surface. The chassis speed is equal to the wheel speed.

100%: the wheel speed is "0", but the chassis is moving (i.e., wheel lock).

The main chassis ECU is in cahoots with the ABS ECU and shares information with it. The chassis ECU knows what gear the Gen II is in and knows what the RPM is so with a little math that should define chassis speed. The Gen I had a VSS which would have provided a very high resolution chassis speed signal.

The FSM goes on to say:

Chassis speed:

 

The speed of the chassis. When the brakes are applied, wheel speed and chassis speed are reduced. However, the chassis travels forward by its inertia even though the wheel speed is reduced.

My speculation: Chassis inertia is continuously calculated from wheel speed. When you apply the brakes the ECUs starts to monitor last known inertia vs wheel speed. At the instant that the brakes are applied reference inertia is known. The rate of inertia change can be calculated by the change in wheel speed, this works because the ABS system keeps the wheel from locking up. There is no need to measure inertia again because it is now a term that is determined by the rate of change in wheel speed. Computers are real good at math :lol: Once chassis speed is below 7 mph there is so little inertia in the chassis that the tires shouldn't be able to slip on wet pavement. In my Gen I supplemental ABS manual it says that below 7 mph that the ABS will be inactive.

Anyone else feel like speculating? I'm sure that when I come back are re-read what I wrote there will be a Rev. 2.

 

[HYCLE]

I haven't found anything that explains all the details of the FJR ABS system. I do have a Technical Orientation Guide with details for a Gen I that was available to dealers which explains things that the FSM doesn't go into, but haven't found one for the ABS. One of the guys that I know through my car club was the GM engineer tasked with developing ABS systems for GM's non-commercial vehicles. I learned a lot of technical things from him, including the first time that I heard about 'slip angle' in his crew's vernacular and 'slip ratio' in Yamaha speak.

The FSM says that the "slip ratio is the value that shows the rate of wheel slippage and is defined by the following formula":

Slip ratio = ((chassis speed - wheel speed)/chassis speed) * 100 (%)

0%: There is no slipping between the wheel and the road surface. The chassis speed is equal to the wheel speed.

100%: the wheel speed is "0", but the chassis is moving (i.e., wheel lock).

The main chassis ECU is in cahoots with the ABS ECU and shares information with it. The chassis ECU knows what gear the Gen II is in and knows what the RPM is so with a little math that should define chassis speed. The Gen I had a VSS which would have provided a very high resolution chassis speed signal.

The FSM goes on to say:

Chassis speed:

 

The speed of the chassis. When the brakes are applied, wheel speed and chassis speed are reduced. However, the chassis travels forward by its inertia even though the wheel speed is reduced.

My speculation: Chassis inertia is continuously calculated from wheel speed. When you apply the brakes the ECUs starts to monitor last known inertia vs wheel speed. At the instant that the brakes are applied reference inertia is known. The rate of inertia change can be calculated by the change in wheel speed, this works because the ABS system keeps the wheel from locking up. There is no need to measure inertia again because it is now a term that is determined by the rate of change in wheel speed. Computers are real good at math :lol: Once chassis speed is below 7 mph there is so little inertia in the chassis that the tires shouldn't be able to slip on wet pavement. In my Gen I supplemental ABS manual it says that below 7 mph that the ABS will be inactive.

Anyone else feel like speculating? I'm sure that when I come back are re-read what I wrote there will be a Rev. 2.

Thanks for the help in understanding, sometimes we teach just what we have been told without a good understanding of facts. We have found errors in old training materials that state "best braking occurs just before lock up". Our instructors are constantly debating our test materials with improvement in mind.

Thanks for the help.