ABS activated at low speed

E28 technical advice asked and given! Troubleshooting, modifications and more.
Post Reply
schulrc1
Posts: 47
Joined: Oct 28, 2006 5:04 PM
Location: Baltimore, Maryland

ABS activated at low speed

Post by schulrc1 »

I have a 87 535, basically stock. The car sat over the winter months and decided to start driving it again due to awesome weather we are having near Baltimore. When i slow down at stop lights or in bad traffic (or similar situations) I have experienced pulsating brakes as I slow from 4-5 mph to a stop. I checked the impedance of the front two speed sensors. The both read the same value (1500 ohms). I removed the front wheels and checked the marks on the hub. I ended up wire brushing and cleaned up the brake region. I was not able to find the end of the speed sensor for the rear wheels so I could verify if those sensor are good. I did Jack up the rear of the car and made sure the brakes were not binding. Any other suggestions for me to pursue. If more info is needed please ask.

Thanks,
Ron
schulrc1
Posts: 47
Joined: Oct 28, 2006 5:04 PM
Location: Baltimore, Maryland

Re: ABS activated at low speed

Post by schulrc1 »

Well I figured out where the ends of the cable for the rear whee sensor are tucked! That’s a slick spot and keeps the connectors from degrading. The impedance of all the sensors are consistent. I brought home an oscilloscope and will take a look at the response as I turn the wheels.
Mike W.
Posts: 26872
Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: ABS activated at low speed

Post by Mike W. »

Are you sure it's the ABS kicking in? IIRC it doesn't work below 5MPH. Is the ABS light on? Pull the black plastic cover off the ABS , pull the relays out and give it a try. That should disable it and if it is or isn't the ABS.

Happens more at speed, but warped brake rotors are endemic with these cars, I put 155K on mine and changed front rotors more often than spark plugs. I do seem to be an outlier though. Just don't discount them.
schulrc1
Posts: 47
Joined: Oct 28, 2006 5:04 PM
Location: Baltimore, Maryland

Re: ABS activated at low speed

Post by schulrc1 »

Well I thought I did a good job checking the ABS toothed rings. The oscilloscope showed a nice repeatable pattern on three of the four wheels. The rear right wheel was the outlier. Carefully inspected the ring again and sure enough it was missing one tooth.
Post Reply