edited Kristian #562 & NickJC # 085i
Many Thanks to Andy #982 for his fantastic Knowledge of Brakes and ABS
Please read the Disclaimer before attempting any work in this FAQ.
Last Updated: 23 March 2007, by Winter #1935

For other related FAQs:


Fuel injected F650's (GS/Dakar/CS) and G650X's have optional ABS (Anti-Brake Skidding, or Anti-lock braking). ABS is designed to reduce the risk of your brakes locking up and causing a rear or front wheel lockup. The system on the F650's is a simply two channel Bosch system - there is no linkage between the front and rear brakes. In other words - if you grab a huge handfull of front brake, the "excess" braking will not be transferred to the rear brake.

The ABS system on our bikes is known as the ABS-N. It is manufactured by Bosch, and the ABS-N ECU was made by Nippon (according to readouts from a GS911). The diagram at the right shows the ABS-N system components in detail.

ABS Is No Substitute

ABS is no substitute for good ol' fashioned braking skills. If you have ABS, do not get lazy - practice braking by turning off the ABS from time to time, and practice your skills in a controlled environment. Also practice heavy braking with the ABS enabled - this will help you understand what it feels like when the ABS engages. This is especially important when you have never experienced the ABS engage.

Also keep in mind your stopping distance. Just because you have ABS, it does not mean you can sit closer to the vehicles in front of you. At a very minimum allow 3 seconds in good conditions. While this is not always possible, it is a good idea to remind people about braking distance.


If you have been working on your brakes, be sure you test them in a safe and controlled environment. If you position the sensor too far from the sensor ring, you may encounter a situation where you have no brakes - this is particularly true on the front brakes (on the rear you will notice other strange behaviour such as an erratic speedo). The following is a quote from someone who has experienced this:

It was VERY scary. At the first squeeze of the lever, it began pulsing and there was ZERO brake force being applied. It didn't have anthing to do with stuck pads at all. After about 100 yards of travel, the ABS unit realizes something is out of whack and disables itself and the brakes function normally again. ... It was due to the gap on the abs sensor being too wide. I removed the shim and all was well. ... gsatlanta

The Speedo, Fuel Injection system and ABS are all affected by the two speedo sensors, and are particularly sensitive to the clearance between the sensor and the sensor ring.

General ABS Questions

How do I know if my Bike has ABS?

What is ABS for?

Can a good rider do better than ABS?

What about off road?

What does the warning light mean?

What is the most common failure/cost of ownership?

Should I modify my riding?

ABS Operation

How do I de-activate the ABS?

ABS on Dirt - Why turn it off?

ABS "Stoppies"

Can a Good Rider REALLY do better than ABS?

Tricks to activate ABS

Does the ABS light come on during ABS activation?

ABS Mods and Maintenance

What is the Sensor gap specification?

What can I do myself to maintain the system?

Can I modify the bike?

Can I add ABS to my bike / Can I remove ABS from my bike?

My ABS doesn't seem to work. Is there anything I can check myself?

ABS Switch Remove the ABS switch and use something to touch the wire contacts together. This is a "normally open" circuit.
ABS fuse Check for a blown fuse.
ABS Warning Light When you turn the key to the on position, the ABS light should turn on for a brief period. If it does not, you probably have a broken globe. If I recall correctly the ABS-N unit will detect and report this fault, so the GS911 should also pick this fault code up.
Battery Voltage Check your battery voltage with the key in the on position, engine off. A 12 volt ABS system typically needs 11 to 15 volts to work. Any less and it cannot tell the 1's from the 0's on digital signals. Check the Battery FAQ for more info.
Front ABS Sensor Check the gap, and check for damage to the sensor. Also check the wire is not damaged, and check the connector tucked up behind the LHS indicator (it is easier if you remove the LHS cover). The GS911 will also detect incorrect signals from the sensors.
Front ABS polewheel These are the toothed wheels on the hubs. Check for chips and missing teeth. Make sure the sensor cannot move in relation to the polewheel. If the signal is not believable, the ABS will shut down. The system needs vehicle speed to work out which wheel is locked.
Front brake lever switch There is a small POS switch on the front brake lever. When you pull the brake lever, this switch activates to tell the ABS and brake light you are braking. If this switch is not functioning, it may affect ABS. The quickest way to check is to see if the front brake lever affects the brake light.
Rear ABS Sensor Again, check the gap, and check for damage to the sensor. Also check the wire is not damaged. The connector for this sensor is next to the BMS-C on the LHS of the bike. Problems with the Rear ABS Sensor will also have other symptoms such as erratic speedo problems, and surging and stalling - this is because the Rear ABS Sensor is also used as the Speedo input.
Rear ABS polewheel See comments for the front ABS polewheel
Rear brake lever switch There is a small POS switch on the rear brake lever. When you push the brake lever, this switch activates to tell the ABS and brake light you are braking. If this switch is not functioning, it may affect the ABS. The quickest way to check is to see if your rear brake lever affects the brake light.
ABS modulator valve This will fire as a test when you set off. If you do this with the rear brake lightly depressed you will get the feed back into the pedal. If the system is active when it should not be (eg low speed, high grip surface stops), you have a sensing problem. A modulator or electrical problem would be detected by the ECU and the warning light would come on.
ABS modulators Do the modulators fire when you first turn the bike on. You should hear a moderate clunk clunk from the ABS unit. If you have a GS911, you will also hear the clunk clunk each time you query the ABS-N unit itself.
Brake light circuit With the key in the on position, engine off... check the brake light turns on and off when you engage the front and rear brakes. If your rear brake light is permanently on, or does not work for one brake lever, you have a failed brake lever sensor. The ABS looks at the vehicle all the time but will only calculate wheel decelerations and fire modulators together during a brake application. If a brake light is stuck on, the system will eventually decide this is a failure and shut down.
ABS-N ECU Query If you have a GS911, or know of someone with one, these devices can query the ABS-N unit for fault codes, and clear them if required. See the Fuel Injection FAQ for more information.
Basic ABS Sensor Checks

You can do a basic test yourself. Unplug the sensors (ignition off) and connect a voltmeter to the two connections on the sensor. Spin the wheel and look at the voltage produced by the sensor. Both sensors should produce the same voltage at the same RPM (typically 0.5V at 30 rpm, but that will vary with sensor types). Voltage should be steady for a steady speed.

Also check for rusty connections, bent pins, or water in the connectors to the sensors. Other things to look out for are split or worn wires.

Connection at Motronic:

Connection at Wheel
(Sensor Detects Slotted Disk as is passes by - Check for Mud, Sensor Mounting Bolts, Brake Disk & Sensor Disk Bolts )

Symptom Based Diagnosis

SymptomPossible Cause(s)
ABS light not turning on 1. No ABS on your bike
2. ABS Warning Light Globe Broken
3. Dash fuse or ABS Fuse Broken
Can not turn ABS off 1. ABS Switch wiring damaged
2. Try rocking bike back/forward a little bit
ABS light starts flashing
(once / 4 seconds)
1. You have turned the ABS off
2. Broken ABS switch or wiring
ABS light flashing
(faster than once/4 seconds)
1. Unknown error / fault
2. Front / Rear ABS sensor problem
3. Main ABS unit problem
4. Perform full system check
ABS light on 1. Unknown error / fault
2. Low battery voltage
3. Perform full system check
Erratic speedo, bucking,
or surging and stalling
1. Rear ABS/speedo sensor fault
2. Water in connectors
3. Loose battery connections
4. Perform full system check
ABS pulsing, Brakes fine if ABS disabled
No bucking / surging or speedo problems
1. Check the rear brake lever switch
2. Check the front brake lever switch
Zero front braking, ABS active
ABS fault after a short distance
1. Front ABS sensor fault (check gap!)
2. Water in connectors
3. Perform full system check

ABS & Brake Bleeding. Can I still do it myself?

Can I turn off the ABS LED?

Opinions on ABS