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ABS Q..D/D.

 
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Arnold
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PostPosted: Sat, Jan 31 2015, 11:33 am    Post subject: ABS Q..D/D. Reply with quote

My 06 Uplander has no codes stored.
When I start it..whether I move it or not..after a little while..the abs light comes on,and a service abs system message.
My code reader says L Rear sensor voltage too low.
I know nothing about abs..and I would leave it but it shuts off the awd.

Q..is this a definite sensor(wheel bearing)?
A No..or a maybe.?

If it was not a definitive I would unplug the sensor and simply plug in another new one and see if that fixes it..then go about changing the bearing if I have to.

It is 0 here and I can't get this into my shop..
It was in for other awd related problems and they did a pretty thorough job of checking everything and could not find anything wrong there.
That was before this happened.

I am guessing the sensor in the bearing went bad and just change it?

I have a new bearing(failed under warranty) and this thing according to the manual the knuckle has to be removed to change it.

I would just like to take this thing in and have them change the bearing and be done with it. Leaving it there..(it is an hr drive..weather/roads here have been bad) and have to go back and get it or wait while they try and find the problem..ya..no thanks.

Are there any definitve wheel bearing/sensor tests?Do wheel bearings/sensors go bad after a little while when the engine has run?
Zero play in the bearing,zero noise,zero problems..awd works..no lights nothing when cold.Driven or not. Start it and wait..or drive it and the problem comes back.

Thanks very much Very Happy for any help!
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wayne petty
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Posts: 3909
Location: cal.

PostPosted: Sat, Jan 31 2015, 12:47 pm    Post subject: Reply with quote

most ABS sensors have a ground wire and a odd version of a 12 or 5 volt circuit.

the sensor has a magnet with a coil of wire wrapped around it.. when the reluctor lines up with the end of the magnet the voltage is pulled low in the coil of wire like you turned on a switch.. when the pole piece is not in front of it.. the voltage goes back up to normal.



this is a hard way to test them in the cold or snow.. and i would NEVER CUT INTO AN ABS HARNESS. i would hit a junk yard and snag a few spare pigtails and try to find the reverse to make a break out pigtail.

all the wheel speed sensors harnesses i have been into were twisted pairs at like 10 twists per foot and foil shielded also.





usually either throwing parts at it.. if you don't have a scan tool that displays wheel speed sensor data while you take a test drive comparing the wheel speeds..

debris stuck to the end of the sensor.. missing teeth on the tone wheel... changing distances from the sensor to the tone wheel because the wheel bearing is failing ..



i only dabble in ABS issues..
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Arnold
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PostPosted: Sat, Jan 31 2015, 1:59 pm    Post subject: Reply with quote

Thanks Wayne..just seems odd that it would not act up when cold..even when sitting..then run for a bit without driving it..and it comes on the same driving and idling.

Speaking of scanning one of these awd systems. I had an awd light on in mine and there was me in the van on the hoist doing whatever and the owner who is a pretty good and sharp tech..online and on the phone trying to find how to scan these codes.
He could not scan them and said I could either throw this GM ONLY dif valve at if for like $500. Or I could take it to the GM dealer..where they would charge me probably more than that just to look at..after dif flushing.

I threw the valve at it and it fixed the problem.

There are just not specs for the performance of these valves.
Only for the full plunger position.
A new valve makes a huge! difference in how they engage and disengage the rear axle for awd.
The valve in mine was going and not throwing codes.
Then it went.
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