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ABS sensor test question


scottdsw

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Hello, I have run into a stumbling block that neither myself or my motorcycle friends can figure out, and hope someone here has greater knowledge. I have read this forum extensively but cannot find a post on how to test the ABS sensor on an 02 1150rt. My ABS faults at around 40mph, steady generator light, flashing ABS light once per second, indicating one of the circuits does not have ABS. From reading the forum, I believe it to be a problem with either the ABS sensor or the ABS controller. I had my local BMW dealer (san jose bmw)read the fault code, and they recommended replacement of the battery, which was done, but the ABS still faults after I gain speed of around 40mph. I checked the sensor gap, and the dealership checked the gap as well, and it is correct. I completely removed the front sensor wire and disconnected it from the white connector on the right side of the bike. It has 2 prongs on the inside. Should there be continuity between the 2 prongs? (when I test it does not) or do I splice into the wire above the sensor to check for continuity. Help would be greatly appreciated. I hope to rule out a faulty sensor wire prior to purchase of the very expensive ABS controller. Thanks so much in advance. I could easily take the bike to the dealer for the checks, but like to gain the knowledge and do much of the work myself.

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Scott, I sure don’t have any resistance data on the 02 IABS sensors but just measured a front sensor form an earlier ABS2 system & it measured 141 ohms (this was at about 74°f)

 

Probably lacking any data from another poster here just measure the rear sensor (they should be close to the same resistance)

 

Make sure your ohm meter is on a scale that will show resistance correctly..

 

Have you tried to move the rear wheel sideways with the rear wheel raised off the ground? Last IABS system I worked on that had a sensor error problem only at vehicle speed was caused by a rear wheel bearing going bad & allowing rear wheel lateral movement therefore sensor gap variance..

 

Twisty

 

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Unhofliche_Gesundheit

re: " I hope to rule out a faulty sensor wire prior to purchase of the very expensive ABS controller"

 

fyi: you may wish to try the test method for saab ABS wheel sensors. i dont say it applies here but worth trying as is fairly easy and quick.

 

disconnect sensor at connector. spin wheel at nice steady speed and measure accross the pins on the sensor side

 

you should get same output on both front and rear wheel

for my car i got 200 milli-Amp AC.

if you get nothing on the milli AC current scale try different scales - might be DC etc.

just an idea.

also you could do a deep dive on the sensors and read their specs...

 

your trouble seems not to appear till you get up to speed - and you cant spin the wheels that fast so this test may or may not be useful. on the other hand i don't see the sensors going 'non-linear' on you - working at low speed but not at high speed (suggesting the module is the problem as the abs is designed to work at all speeds.

 

maybe try locking the wheels up at low speed on gravel and see if abs system kicks in. would suggest wheel sensors working.

 

cheers.

 

 

 

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re: " I hope to rule out a faulty sensor wire prior to purchase of the very expensive ABS controller"

 

fyi: you may wish to try the test method for saab ABS wheel sensors. i dont say it applies here but worth trying as is fairly easy and quick.

 

disconnect sensor at connector. spin wheel at nice steady speed and measure accross the pins on the sensor side

 

you should get same output on both front and rear wheel

for my car i got 200 milli-Amp AC.

if you get nothing on the milli AC current scale try different scales - might be DC etc.

just an idea.

also you could do a deep dive on the sensors and read their specs...

 

your trouble seems not to appear till you get up to speed - and you cant spin the wheels that fast so this test may or may not be useful. on the other hand i don't see the sensors going 'non-linear' on you - working at low speed but not at high speed (suggesting the module is the problem as the abs is designed to work at all speeds.

 

maybe try locking the wheels up at low speed on gravel and see if abs system kicks in. would suggest wheel sensors working.

 

cheers.

 

 

 

 

Cameron, actually he can spin the wheel that fast.. Just needs to hook the meter up to the sensor in question then ride the motorcycle while watching the meter.. Problem is a lot of digital meters will just average the reading so might not show an erratic type failure.. Really need a scope to get a true sensor output trace especially as the pulses increase due to tone ring RPM increase..

 

Twisty

 

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thank you VERY much Cameron, a great idea. I will follow your suggestion, reconnect the ABS sensor, and check amperage at the other end of the connection plug with the bike moving at speed. Since the fault usually occurs around 40mph, I may not detect a problem until that speed is reached. Thank you so much again. After performing the test I will post my results to help any others with the same problem

take care,

Scott

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Anton Largiader

IABS isn't like ABS2. ABS2 uses AC inductance sensors but IABS uses 2-wire Hall sensors. I can't see you getting a signal when they're not powered. Also I don't see it as a good idea to try to test for continuity across them.

 

Leave them connected and find a way to read the voltage across the two leads when you spin the wheel. Of course if the problem only shows up at 40 mph, testing might be difficult.

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IABS isn't like ABS2. ABS2 uses AC inductance sensors but IABS uses 2-wire Hall sensors. I can't see you getting a signal when they're not powered. Also I don't see it as a good idea to try to test for continuity across them.

 

Leave them connected and find a way to read the voltage across the two leads when you spin the wheel. Of course if the problem only shows up at 40 mph, testing might be difficult.

 

Anton, you can measure the signal on an ABS hall sensor.. Best is a scope,, next is voltage fluctuation but as you mention it must be hooked up & powered from the controller as the tone ring just varies voltage based on tone ring metallic position (real close to a digital wave signal) .. Another way is with the meter on resistance & sensor disconnected.. This should show a resistance change as the wheel is rotated but unfortunately not a real accurate way of telling correct output & will probably not respond fast enough to show resistance change at anything over a slow wheel rotation..

 

The brake group at work here always uses a scope to verify correct hall type wheel sensor wave pattern..

 

Twisty

 

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Had a similar situation on my 1998rt.Found the front wire loom right down by the wheel with an open circuit.By hooking up the meter and watching my 141 some ohms resistance i bend and twisted the loom till i found it.That seems to be the spot where the loom tends to break.It's mostly the front sensor and not the rear.

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Guy on the BMWMOA forum posted on the same problem. Turned out he had corroded connectors in the fuse box. Cleaned them up then used Corrosion X,...problem solved!

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Thanks very much for the suggestion of checking the fuse box connector. If the sensor wire does not have a problem, that is another excellent idea. I suspect to be doing quite a few of the mentioned tests over the next several days, thanks to all for the excellent and friendly help.

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