ABS and a car wash

Are sure that the sensor didn't get *disconnected* by the car-wash?

There could have been metallic particles on the sensor or the pulse wheel which were washed off (or at least displaced) during the underbody wash. Find an empty side street or parking lot and d a real-world test the operation of the system.

__ __ Randy & \ \/ /alerie's \__/olvos '90 245 Estate - '93 965 Estate "Shelby" & "Kate"

So those sensors aren't "sealed"?....the washing could have possibly cleaned them (somewhat)?

So far, so good....not a single ABS warning light.

I guess I should do some hard stop and go just to see.

The sensor is a magnetic/electromagnetic device. It has a magnetic end that "senses" the passing of many hunbreds of what look like gear teeth that are part of the rotor/hub. The magnetic pulses are received and sent to the computer which combines various signals to decide if a wheel is about to lock up and the computer modulates the poressure of the brake system to that one wheel to keep it from locking up.

The sensor's wiring is sealed. What happens is that the particles of the disc and brake pads as they wear can get stuck to the magnet end of the sensor. The magnetic field is quite strong there. If these build up to much they affect the sensors ability to "see" the teeth going by. The cure is simple- carefully remove each sensor and wipe the particles off the end, althe time being careful not to stress the wire connected to the sensor any more than necessary. Remvoeing them once in a while is good becasue you can smear a little brake silicone or anti-seize to the sensor to keep it from corroding into place.

Jacking up one wheel at a time and using the tool kit in the car I believe that you should be able to remove the sensors yourself.

Same with my wife's 960. Threw the light a few times and I knew it was time to clean the sensors.

If nothing else, it is a really good idea to experience what the car can (and can't) do in an emergency and to feel what the ABS system feels like. Get it up to about 40-45 and hit the brakes- don't slam the pedal, but smoothly and rapidly press it as far as it will go until you stop. It might take two or three times to get the feel of it, but your car (most cars, actually) can stop a lot faster than you think! Let the brakes cool for a couple of minutes between tests so as not to overheat and warp the rotors.

If the car seems to "hop" on the front end or chatter excessively it could be a sign that the front struts need replacing. I noticed a dramatic improvement in ABS performance after I had replaced the 960's front struts.

__ __ Randy & \ \/ /alerie's \__/olvos '90 245 Estate - '93 965 Estate "Shelby" & "Kate"

IIRC a common advice (by knowledgable Volvo people here, rather than me!) used to be to clean the castellated area at the end of the axles when the ABS light came on, to clean the accumulated debris out. It isn't the sensor per se, but the part that goes past the sensor they were concentrating on.

Mike

Well the car wash was wishful thinking.

Started acting up again.....but it could possibly indicate a loose connection......never the less, I'll clean all the sensors.

I wonder if a blast of air from an air gun would clean them?....or is that a bad idea?

It shouldn't be all that hard. Remove each wheel and you should see the cog area that makes up the ABS reluctor, just behind the bearing carrier. Where something gets close to the teeth, that has to be the sensor. A brush on the teeth and a blast of the air gun on the part of the sensor facing the teeth should clean it up.

Mike

And if you don't own an airgun, the compressed air in a can at computer shops works well for this.

The connectors are under the hood near the wheel arches in the front, and of course the connector on the ABS unit itself, it's easy enough to clean those too.