2001 v70 2.4t How to test wheel sensors

chaurik · Post by **chaurik** » 18 Dec 2014, 15:04

Hi guys, new to the site and my first post. I have a 2001 volvo v70 2.4t fwd. I have been getting some abs/tracs lights for a while. Eventually I got, "brake failure pull over asap", odometer doesn't count up, trip is dashes, speedo works, no cruise. After some research I decided to replace the abs module which had no change and now I have a p1633 (vss signal) which came on not long after the replacement I recently went through the whole front end and replaced both cv shafts and wheel bearings amongst all suspension. One wheel bearing in the rear is new and the other is old but no indication of issues. I am guessing that I have a wheel sensor messing with me so I got my trusty meter out to check resistance and continuity. I had no continuity on both front wheel sensors so ordered two new ones which are also open. I have always tested these this way but apparently these are different. Any advice is appreciated on how to test them or a diagnosis of my symtoms, thanks in advance!

Post by **vtl** » 18 Dec 2014, 17:02

You need to turn the wheel. It has a magnetized ring with teeth, sensor generates a tick each time tooth passes nearby.

I'd advice to read the codes with DiCE.

draser · Post by **draser** » 18 Dec 2014, 17:13

The sensor has a so called Hall cell that generates voltage pulses when the trigger wheel rotates. I'd try the voltmeter on mV across terminals.

chaurik · Post by **chaurik** » 18 Dec 2014, 17:30

Thanks, I will check it and get back to you. Do you guys think I'm on the right track? Anything else suspect that I should check?

Post by **vtl** » 19 Dec 2014, 09:16

If you read the code with DiCE+VIDA setup you'll know what failed exactly, or at least what your car suspects to be broken.

chaurik · Post by **chaurik** » 20 Dec 2014, 18:36

What is that? Where do I get it and how much $. I tried spinning the wheels and checked ac and dc m.v. and nothing, even checked frequency, nothing. tried the new sensors and set up my cordless drill to spin past it and nothing. I have no idea how to test these things. I might have to go to the dealer, hard part is they're an hour away and then I've got to pay diagnostics. Might be better off since I've already got money invested and over 100$ worth of sensors on the table that might not fix it but can still be returned.

draser · Post by **draser** » 21 Dec 2014, 07:48

Try with sensor connected as it needs a polarizing voltage to function. Back tap the wires with needles, make sure the meter is on mV only, do not use mA or ohms as it will short out the circuit.

Post by **JRL** » 21 Dec 2014, 10:02

*****

Post by **jimmy57** » 21 Dec 2014, 10:37

It is a two wire sensor called a magnetic resistive element (MRE).
The resistance changes with magnetic field changes. Volvo specs for this type sensor list it as 7 mA not affected (tooth not next to sensor) and 14 mA affected (tooth aligned).
The voltage change if read as voltage is minor, like 10-15 mV.
It is not readily visible when viewed on oscilloscope.
Ammeter in series is the best but that requires jumper leads be fashioned.
VIDA is the best way (some other scan tools also show individual wheel speeds also. Autologic, Autel, Launch, and some sold by professional tool sellers will have ABS parameter displays.

chaurik · Post by **chaurik** » 27 Dec 2014, 09:50

Thanks for the advice everyone. As it turns out the reman module needed software installed. Took it to the dealer and their computer said "hardware doesn't match vehicle". Called fcp where I got it from and they dont have an answer, part numbers match but wont take software. Anyone have an old module with part # 8619544 laying around they want to dump?