ABS issue .. Looking for a Wabco S446-004-426-0 (I think)

[wyle.e.kyote]

I've recently had the ABS light go on in my 2000 H3-45.   And by on I mean always on.     The blink button does not cause it to blink, it remains on no matter what (short of pulling the breaker)       Usually you could flip the switch and get whatever code out of the wabco that was currently pissing it of and go repair that.  This time though, the ABS light stays on as soon as power is applied.       I've checked the wiring that can be checked..  its getting +24 where its supposed to be  and ground where its supposed to be.  The various wheel sensors appear to be intact and when you spin the wheels little pulses show up on the scope as one would expect as the shaft spins past the hall-effect sensor.

Its also disappeared from inventory.   What I mean by this is that my ProIQ shoes the DDEC, The Allison and prior to Sunday showed the WABCO ABS module.   Now it doesn't.     It just shows the DDEC and the Allison.    

Prior to its untimely departure from inventory it came up as the following

Brakes, Power Unit - WABCO - Vehicle Info
Software Revision: D15 Serial Number: 002416 Manufacture Date: 22/1998 Part Number: 8840044200 Configuration: 4S/4M
ECU Type: Unknown
Make: Meritor WABCO Brakes (Air)


According to the sticker on the box its a P/N S446-004-426-0   which other than various websites in the former soviet union and some chinese guys selling knock offs  ( I think)   I can't seem to find it online.    

I was about to head over to Prevost and pay the ignorance tax to get them to look at it, but before I did that I thought I'd through one shot out to the intertubes and see if anyone has other ideas or has the captain midnight decoder ring to turn that into a part number that can be found.

Thanks!

[Len Silva]

http://www.ebay.com/itm/New-Monaco-RV-Wabco-Meritor-ABS-ECU-Module-S446-004-426-0-4S-4M-D-Cab-12V-/320862565075

[belfert]

Go to www.wabco-auto.com and click on product number.  Enter 446 004 426 0 in the search box.  Also, click on Publications and enter ABS and it will list four pages of ABS documentation.  Have you check the resistance on the sensors?  I'm not sure what resistance Wabco sensors are supposed to show.

You can try calling 1-800-535-5560 to see if you can get technical support from Wabco.

[rv_safetyman]

Doug, not many folks on this forum will have ABS knowledge - we all drive old clunkers

I am sure you have done a search, but I did a search on "Wabco + ABS + diagnostics" and got a lot of hits.

Sorry, not much help.

Jim

[belfert]

I'm certainly not familiar with the wiring on a Prevost, but I know on my Dina the ABS light would not come on at all if the ABS unit had no power, or if the unit was dead.  The signal for the ABS light in my bus comes from the ABS unit directly.  In my bus the ABS controller is stand alone and not connected to the data bus in any way.

Your bus is five years newer than mine and it appears your ABS unit is connected to the data bus in your coach.  It could be that the ABS light comes on if there is no communication over the data bus to the ABS controller.

[Brian Diehl]

I have a Wabco 6S/6M 12v unit.  Would this be of any interest to you?

[wyle.e.kyote]

http://www.ebay.com/itm/New-Monaco-RV-Wabco-Meritor-ABS-ECU-Module-S446-004-426-0-4S-4M-D-Cab-12V-/320862565075

Thanks Len, this one won't work as I'm a 24vdc sytem and the Monaco is a twelve.

Go to www.wabco-auto.com and click on product number.  Enter 446 004 426 0 in the search box.  Also, click on Publications and enter ABS and it will list four pages of ABS documentation.  Have you check the resistance on the sensors?  I'm not sure what resistance Wabco sensors are supposed to show.

You can try calling 1-800-535-5560 to see if you can get technical support from Wabco.

They are hall effect switches .. basically they operate when a magnetic change happens because a piece of metal crosses nearer to them and then is removed.  I'm sure there's a resistance check but I've not found it --   I can however monitor the sensor leads using an oscilloscope and see the pulses go by when I rotate the appropriate wheel.        Also, if it was a  wheel sensor I'm supposed to be able to pull the trouble code out via the blink switch .. On my unit it never seems to get into that mode.

I've called them prior to posting this and they sent me a troubleshooting guide .. after that they basically wash their hands of me as they want an actual professional to look at it opposed to a garage hack like myself. 

Doug, not many folks on this forum will have ABS knowledge - we all drive old clunkers

Yes, but there are (from all appearances) more do it / fix it yourself folks here which makes me feel more at home.

Your bus is five years newer than mine and it appears your ABS unit is connected to the data bus in your coach.  It could be that the ABS light comes on if there is no communication over the data bus to the ABS controller.

I thought about this too, its possible the data line has failed somewhere.  I asked Meritor-Wabco about it and they didn't know.    I've been thinking that I should be able to use my scope to test this case .. Not sure what to look for, but if the patterns look the same as whats pouring out of the DDEC connector, then I can presume its getting the right signal down there.  I will probably go try a few things with it in this area.

I have a Wabco 6S/6M 12v unit.  Would this be of any interest to you?

I don't think I can use it.  I'm a 24vdc 4S/4M system. 


Thanks for the responses folks.

[belfert]

Go to www.wabco-auto.com and click on product number.  Enter 446 004 426 0 in the search box.  Also, click on Publications and enter ABS and it will list four pages of ABS documentation.  Have you check the resistance on the sensors?  I'm not sure what resistance Wabco sensors are supposed to show.

You can try calling 1-800-535-5560 to see if you can get technical support from Wabco.

They are hall effect switches .. basically they operate when a magnetic change happens because a piece of metal crosses nearer to them and then is removed.  I'm sure there's a resistance check but I've not found it --   I can however monitor the sensor leads using an oscilloscope and see the pulses go by when I rotate the appropriate wheel.        Also, if it was a  wheel sensor I'm supposed to be able to pull the trouble code out via the blink switch .. On my unit it never seems to get into that mode.

Bendix ABS sensors are supposed to ohm out between 1,500 and 2,500 ohms.  A lot of air brake stuff is interchangable, but no idea if ABS sensors are or not.

It seems like your issue is probably not wheel sensors, but they are easy to check.  I'm sorry Wabco was not more help.  Bendix has been pretty helpful to me for some that is 17 years old and obsolete.

[luvrbus]

Just plug in a Pro/link in it will tell all you need to know,I am going buy stock in Pro/Link looks like a lot of people here need one lol

[wyle.e.kyote]

Just plug in a Pro/link in it will tell all you need to know,I am going buy stock in Pro/Link looks like a lot of people here need one lol

I've got a prolinkIQ. it tells me nothing ..  its like the ABS isn't there as it no longer shows up in inventory. 

[luvrbus]

Do you have the right software for your system ? could be the software needs to be reinstalled isn't that a Knorr brake system on your bus Prevost does some kinky stuff with the ABS and only they have the key

[wyle.e.kyote]

Do you have the right software for your system ? could be the software needs to be reinstalled isn't that a Knorr brake system on your bus Prevost does some kinky stuff with the ABS and only they have the key

Prior to Sunday (last sunday)  the WABCO ECU showed up in inventory.   I think thats a good sign that I've got a working key.

[wyle.e.kyote]

For those of you waiting with baited breath for the results ..  Prevost replaced the ABS ECU.      The exact words from the ticket are

OPERATION CODE 12.02
Complaint:ABS LIGHT ON
Cause:ABS ECU MODULE FAILED
Correction:CHECKED THE ABS SYSTEM AND FOUND THAT WE WERE UNABLE TO CONNECT WITH THE PRO-LINK. VISUALLY CHECKED ALL WIRES AND FOUND ALL OK. GOT A NEW MODULE FROM STOCK AND INSTALLED ON THE COACH. ROAD TESTED THE COACH AND ALL ABS LIGHTS WENT OUT AND IS WORKING FINE AT THIS TIME.
I10 Internal Labor
641538 ECU-ABS 4 CHANNELS

At $1200 (all in) it was actually less money than I could find the modulator online .. go figure..