Wheel sensors

Took some time today to go after the lights coming on the dash--Trifecta--The back sensors were worked on this afternoon and they were really crudded up. The one on the drivers side had light scratch marks across it --I saw the scratches after I had given it a good cleaning. I replaced that one with a new one I had on hand. Test drove and the lights stay off--drove all over the place and no lights--got home and parked the car and they came on again--Went for another test drive and No lights again.
Here's my question--I cleaned one sensor and replaced the other--the crud was bad on both so I spray some brake cleaner down the sensor wells to try and clean up in there--question should I have turned the rotor's while doing this to make sure I cleaned all around the hub where the sensor gets it's info--of course I should but how do you do this with only one wheel off the ground--?

You should be able to turn either rear wheel with the other one the ground as long as the tranny is in neutral or you don't have an LSD diff.

Thanks Jim--I thought about this later after I had cleaned up and all--still hitting myself in the head for not thinking it out while I was in it--Oh well--At least the lights are out most of the time now instead of being on all the time--was getting ready to ship out the ABS control for the work to be done on it--I'll drive to work this week and try to redo what I missed next weekend.

Hope you let contact cleaner dry well before driving. No need to rotate wheel at all to clean sensor. I would remove and clean tip and dry. Scratches are not good. Not necessarily killer either. I wouold tell you to do multi-meter test, but it is in here many times and do if you believe what I say or do your own thing. Error after driving short distance points more to module getting even a little heat. Solder connections go bad and slightest temp change can make them good and bad. Your good candidate for BBa re-build. Do not replace any more speed sensors till you can remove yours, clean with dry, soft town on end and contact cleaner inside boxes where they have pigtails connecting with blue connector to cable. That box will be full of **** you can clean out and spray your contact cleaner here.

Originally Posted by poolman

I thought about this later

Makes me remember that I always wanted four jack stands (I only have two serviceable ones) so I can work on all four wheels at once!

I know you know about the ABS test procedures from 540iman, but, for others, they're outlined in detail here:
- How to diagnose the BMW ABS BRAKE DSC/ASC trifecta (1) & why the 5-minute ABS DIY quick test doesn't always work, especially on brand new non-OEM wheel speed sensors, by Quick99Si (1)

Originally Posted by poolman

was getting ready to ship out the ABS control for the work to be done on it.

I know you've been on a long time so I might be preaching to the choir but, as Bill noted below, you don't mention wheel speed sensor DMM test results - so I'm curious whether you've run that test. Also, there 'are' six other tests of the wheel speed sensors - but again - I know you know about them so I'm just curious.

And, you probably know that BBA is best and that they run $98 Ebay specials (apparently including two-way shipping), so, if the module does go out for a fix, that's the way to go.

Lastly, if/when you do send it out for repair, my suggestion is to mark the unit's two black boxes (on the back) to see if they replace them, and, to ask, while your unit is on the test jig, what they find and what they fixed (we all want to live vicariously through you and others).

Originally Posted by 540iman

I would tell you to do multi-meter test, but it is in here many times and do if you believe what I say or do your own thing.

I'm curious about the results too. Mine are below. I think consistency is the key thing to look for in good sensors.

Originally Posted by 540iman

Error after driving short distance points more to module getting even a little heat.

I realize I'm not adding much value here - as everyone on this thread is a regular - but I wonder if there is a "cold" freeze spray that Poolman can shoot onto the ABS control module when the trifecta lights up. Most people go the other way (hair dryer) to make the lights turn on - but it would be diagnostically useful if Poolman could cool his ABS control module when the lights do go on.

Don't use brake cleaner to clean electrics! Much too harsh. Use contact cleaner for electronics and use brake cleaner to take grease off anything as it is potent.

Poolman, when I cleaned my speed sensors, I used Q-tips for the receptacles, and the surroundings. Mine were also crudded up, but no trifecta.
I believe that while contact cleaner is a recommended solution for contact cleaning, the wheel sensors are OK with brake cleaner. They are encapsulated, and also they get crudded up by brake dust, rotor particles and road debris. I believe they are sturdy enough to take the brake cleaner. There is no "outside" sensor per se you clean/touch. The sensitive stuff is well protected. Brake dust and rotor shavings that get stuck on to the outside of the sensor might be magnetized, throwing the sensor reading off.