ABS help please

[bigskymt]

My '04 Newmar/Freightliner is displaying an ABS Light on the dash as well as warning on the Freightliner Display.
I've removed each ABS Sensor plug from it's appropriate brake controller and measured resistance across the three pins. All readings were in the 5-9k ohm range except the drivers front wheel: 5.3k ohm, 5.6k ohm and 0.4 ohm, effectively a dead short. the cable appears to be undamaged.
I'm clueless when it comes to removing the sensor from the hub and hope someone can offer some advice before I cause myself an extra repair bill.

Thanks in advance

["007"]

Maybe this will help or not. Scroll down to ABS info.
I just had the brake recall done and I have a ABS indication on my dash.
The sensor and mounting need to be cleaned for the sensor to indicate everything is OK.
I've had problem before and have clear by cleaning and after a couple of starts the ABS System would be reset.
If not you can get a new one from Oemy.

[bigskymt]

Thanks 007: I eventually called Freightliner Help and explained my situation. As instructed I pulled both front sensors and cleaned them then "tapped" them in place. I then drove the required 8+ MPH several times with no results. Freightliner Help could not explain the .4 ohm resistance where every other sensor input to the brake controller was 5k ohm+. I'm searching for schematics to find what module the sensors feed before entering the brake controller.
At least i learned to remove sensors w/o damage.
thanks again

[RRGuy]

I had a similar problem last year. Freightliner found a misrouted wire to one of my wheels which was frayed or broken. It took over six years to manifest itself.


John Abbott
2004 Winnebago Journey 39'

["007"]

The misroute was also brought up when I had brake recall done the lines for ABS at both rear wheels was along the top of chassis rail and shop thought they might be crushed the way they were placed.
They tried to reroute but line lengths would not allow.
Never had a problem with the rears it was always the front ones.
I'd check the wires and see if they are all clear of the frame when suspension may operate up and down even when you deflate the air bags wire not caught between a bag.

[bluepill]

If the sensor pickup is designed like those on cars, it is many, many turns of very, very fine magnet wire wound around a solid iron core. Because the wire is so fine, it can break or short between turns from vibration, contamination, or brake heat. Besides an ohms test, you can look at the waveform produced with the wheel turning if you have access to a DSO. Otherwise, substitution would be the best diagnostic tool.

["007"]

Thanks for that bit of information bluepill.
I hope the blue pills are not the ones I take.

[bigskymt]

I spoke with Freightliner again after their "fix" failed to have any effect.
Once I got into ohms readings tech support said that was too complicated for them and I would have to take it to a Ftl Dealer to read the code.
FWIW: If I remove the suspected sensor from the backing plate I no longer read a dead short across two of the three pins that plug into the controller. Disconnected those two pins read like a cap under ohms test, same using diode test. Ftl did fax me schematics which helped and will help more once I locate the ABS controller.
Once the weather improves I'll be back at it.
After reading all the positive posts about 1-800-FTL-HELP I'm probably the only one who is not impressed with their support.
Bluepill: good idea. I have a storage scope and will try to read waveforms once I raise the wheel and rotate it.

[bluepill]

Just compare signals between good and suspect units. Tap the suspect sensor and wiggle the wires while testing, 'cause it now sounds like an intermittent.

Good luck