ABS not working on rear only.

[Love2Ride]

I have a 2006 BMW R1200GS. Manufactured 27/06/2006. 1170cc. 74Kw. I first noticed my brakes warning light flashing rapidly about two months ago. With this I realized that my front brakes work 100%, including the ABS but the rear brake feels very hard to apply and ABS does not work on the rear at all. With the bike on the centre stand, ignition on (engine not running), you can clearly hear the servo running when you pull on the front brake, but the servo does not run when the rear foot brake is applied. I have now bled the abs for the third time with no positive results. I had a guy do a diagnostic with a “OBDLink” and the following codes came up:
Before clearing the codes, 4 came up:
1)   Wheel speed sensor, rear. 61F0
2)   Wheel circuit, rear: 618C.
3)   Brake fluid level: 6269.
4)   Internal control unit fault 624D.

And after clearing codes 1 came up:
1)   Wheel circuit, rear: 618C.

Can anyone help by explaining this “618C” code? Or how to rectify the problem.

[Alexm1]

I am not familiar with the OBD link but have experienced a similar problem on a 2003 K1200rs and the final fix was to replace the abs unit with a second hand unit that was known to be good.
I am assuming you bled the wheel circuits as well as the abs circuits and that they are correct.
Check the rear wheel sensor clearance to ensure it is correct.
I did service the abs unit per a post on this site by jughead but with that done, bleeding done and all adjustments correct and still no fix the unit was all that was left.
I have not worked on a 2006 model but on the 2003 the abs unit replacement is an easy job.

[WayneC]

I had a guy do a diagnostic with a “OBDLink” and the following codes came up:
Before clearing the codes, 4 came up:
1)   Wheel speed sensor, rear. 61F0
2)   Wheel circuit, rear: 618C.
3)   Brake fluid level: 6269.
4)   Internal control unit fault 624D.

And after clearing codes 1 came up:
1)   Wheel circuit, rear: 618C.

Can anyone help by explaining this “618C” code? Or how to rectify the problem.

An OBDLink is only a hardware interface, what software was used is a good question & it sounds, as expected, that the generic software is only capable of reading & clearing fault codes plus is unable to recognise the fault codes & give fault code descriptions, that is a long way from "doing a diagnostic"

[Love2Ride]

Alexm1, thank you for your reply. What should the clearance be on the rear wheel sensor? Is the clearance not a set distance one it is in place and bolted down? Can it be changed? Will a incorrect gap or faulty rear sensor not have an effect on the speedometer?

[Love2Ride]

I had a guy do a diagnostic with a “OBDLink” and the following codes came up:
Before clearing the codes, 4 came up:
1)   Wheel speed sensor, rear. 61F0
2)   Wheel circuit, rear: 618C.
3)   Brake fluid level: 6269.
4)   Internal control unit fault 624D.

And after clearing codes 1 came up:
1)   Wheel circuit, rear: 618C.

Can anyone help by explaining this “618C” code? Or how to rectify the problem.

An OBDLink is only a hardware interface, what software was used is a good question & it sounds, as expected, that the generic software is only capable of reading & clearing fault codes plus is unable to recognise the fault codes & give fault code descriptions, that is a long way from "doing a diagnostic"

Thank you for your input WayneC. I am a bit new at all this diagnostic stuff. I will have to follow up with the guy that checked it for me. He did look a bit unsure of what he was doing in the first place, although he told me beforehand that he is not a BMW mechanic as such.

[Jughead]

Hi Marco

Apologies for the late reply.

Unfortunately the codes from the OBDLink unit is a little vague.

However, the fact that it brings up the rear wheel speed sensor appears to indicate that there is a problem there.  Two things you can check.

Follow the cable from the sensor up along the rear torsion bar.  At the front just above the swingarm pivot point, the cable will leave the torsion bar and follow the frame.  Just at the transition between torsion bar and frame the cables sometimes get pinched and broken, resulting in the sensor failing.  In the photo below, the cable (blue arrow) has been known to be pinched in the gap indicated by the red arrow.



If all is well there, then remove the sensor from the final drive and inspect the end of it.  If the end is full of metal bits (it is after all a magnet) that would indicate a bearing failure in the FD and also at times cause the sensor to fail.

[schuppi]

Hello

Fault code means:
618C   24972    Pressure in rear wheel circut is to high      

Pressure measurement at ignition on in the rear wheel circuit  over 30 bar. A defect of the sensor is probable and a replacement of the module is recommended

[Jughead]

    

Thanks Schuppi.  Sorry Marco.  Just looked at your post again and I was looking at the wrong code.

The "Pressure in rear wheel circuit too high" points to a faulty sensor inside your ABS pump.

The sensor is incorporated with the front wheel sensor and looks like this.

Inside


Outside


And it is located here, on the LHS of the pump as viewed from the rider's seat.

[Love2Ride]

Hi Marco

Apologies for the late reply.

Unfortunately the codes from the OBDLink unit is a little vague.

However, the fact that it brings up the rear wheel speed sensor appears to indicate that there is a problem there.  Two things you can check.

Follow the cable from the sensor up along the rear torsion bar.  At the front just above the swingarm pivot point, the cable will leave the torsion bar and follow the frame.  Just at the transition between torsion bar and frame the cables sometimes get pinched and broken, resulting in the sensor failing.  In the photo below, the cable (blue arrow) has been known to be pinched in the gap indicated by the red arrow.



If all is well there, then remove the sensor from the final drive and inspect the end of it.  If the end is full of metal bits (it is after all a magnet) that would indicate a bearing failure in the FD and also at times cause the sensor to fail.

Hey Jughead, just checked cable and sensor, seems fine.

[Love2Ride]

   

Thanks Schuppi.  Sorry Marco.  Just looked at your post again and I was looking at the wrong code.

The "Pressure in rear wheel circuit too high" points to a faulty sensor inside your ABS pump.

The sensor is incorporated with the front wheel sensor and looks like this.

Inside


Outside


And it is located here, on the LHS of the pump as viewed from the rider's seat.

Thx Jughead/Schuppi. As mentioned my fault code reads "Wheel circuit, rear: 618C". Where can I get this sensor (on the ABS pump). And I suppose you have to remove the pump to replace the sensor? Jughead, could you please direct me to the video on the correct way to bleed the system. I have wached a few and they all were different. My name is Basie, by the way.

[Love2Ride]

Just to clarify something. I have bled from the lever (front brake) and the foot brake pedal mechanically and then using the ABS pump motor to bleed from the pump to the two front nipples but the back I cannot do from the pump to the rear wheel because the ABS pump will not run when I push on the rear brake pedal.

[Jughead]

[youtube]https://www.youtube.com/watch?v=d5sJjnHPv2Q[/youtube]

[schuppi]

Hello

If this fault is stored in the unit, there will be no function of rear pump.
So the bleeding of the rear system will not be executable

[Jughead]

The pump will not run if the error is currently present, and you cannot clear the error because it is currently present.  You need to resolve the issue first (remove the source of the error) (Error not currently present) before you can clear the error and operate the pump.

[Love2Ride]

Ok, thx guys. I did bleed the brakes in the right sequence except my reservoir to catch the old brake fluid was below the pump and the calipers (on the floor). Well, all of that is useless until I fix the source. So, I think I will first swap the two pressure switches on top of the pump to see if the problem shifts to the front brake and then I will take the unit out of the bike, remove the sensor off the side of the pump and see if I can source a another sensor somewhere. If anyone has an idea where to get a sensor if will be much appreciated.