Faulty Wheel Speed Sensor

[brumster 135 1 Cars]

So the missus' Jeep has got what I think is a dodgy wheel speed sensor, reasoning being the "service electronic brake system" and "service 4wd system" notifications have started flashing up on it, and I've noticed in reverse on hard lock you can feel the QuadraTrac II 4WD system locking up the rear diff, which I suspect means it thinks a wheel is slipping... when it actually isn't. Sounds fair?

 

So, on that basis, I need to figure out which wheel speed sensor it is. Curiously, my OBD tool isn't showing any MIL codes up, which means 1 of 2 things - 1, it's not a wheel speed sensor or 2 my cheapy ELM327 OBDII tool can't pick up the right OBD codes. I'm hoping it's the latter.

 

So, short of a visual inspection showing one wheel speed sensor in complete tatters, how would I test one - hook up an oscilloscope to the bounder and spin the wheel? Or just a straight resistive test on each one and spot the "odd one out"?

 

The sensors are only £15 a corner but not sided, so one possibility is I just buy a front one and a back one, swap them and trial and error it... :-S

Edited September 21, 2011 by brumster

[cybernck 403 1 Cars]

My old 405 T16 had ABS rings with dense teeth that used to get clogged up with dirt or corossion and give ABS sensor fault codes - just an idea .

 

 

(third post in a row mentioning my old 405 T16 )

[brumster 135 1 Cars]

Good point; I'll give it all a good check-over and clean it up if need be. I've heard of this problem on Jeeps that are getting clobbered with mud all week, but of course this one just sees tarmac 99% of the time... but it could be something in there nonetheless...

[welshpug 1,666]

checking resistance is a good place to start, eliminates the wiring as well, autodata shows how to do it from the abs ecu multiplug which is usually on the abs unit.

 

you can use a power probe to test them too.

[brumster 135 1 Cars]

Eyeballed all four tonight and they don't look physically damaged or clogged, wires intact and multiplugs checked under the arches, unplugged and plugged back in. The "service 4x4 system" message has disappeared so clearly I've helped something, but the "service electric brake system" is still flagged up. No error codes on the OBDII. Feckin' strange; will check the resistances next, hopefully it is a duff sensor outright now...

[brumster 135 1 Cars]

Sorted it; left hand sensors were at 20Mohms and the right pair had no continuity at all. Ordered the bits... fingers crossed there's nothing else hiding behind the reason for a double failure :-(