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Old 03-28-2014, 11:18 PM   #1
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ABS Dash Light On and Noise

A few weeks ago the ABS light on the dash came on during a very short drive to a local repair facility when I had to take the coach in for radiator repair and refrigerator compressor replacement. Thankfully I still have an extended warranty! Anyway, It was very cold out so I didn't immediately investigate it but mentioned it to the tech at the repair facility who said they would run a diagnostic check and read the code(s). A week later when I picked up the coach the shop told me they didn't get around to checking on it. I was just glad to finally get it back, so I drove it home and parked it. Also, I thought the inverter/charger fan sounded louder than usual which made me think that the fan motor was going bad.
Today, it was finally warm enough for me to check into both these new issues. I found out that the noise I thought might be my Xantrex fan going bad was really coming from the ABS module, if that's the right name for it. It almost sounded just like a mixing pump on the Aqua Hot or like I mentioned above; a louder than usual Xantrex fan noise. I crawled into the compartment just forward of the rear tires (picture 1) and found the source of the noise (pictures 2, 3, & 4). I unplugged the wire connections one-by-one, and of course the last one I unplugged (picture 3) made the "whirring" noise stop. The module was of course warm to the touch and had apparently being "running" for the last three weeks ever since the ABS dash light came on. Has anyone else experienced this problem? What is the recommended procedure for troubleshooting and/or replacement? Did I damage the module by letting it run for so long? As usual, any advice is much appreciated.
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Old 04-01-2014, 02:56 PM   #2
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Anybody ? Am I really the only one that has ever had the ABS Module go bad?
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Old 04-01-2014, 04:52 PM   #3
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I have not had problems with the ABS. Did you try putting the plug back in to see if it would stop making the noise? MY suggestion would be to look up ABS problems on the internet to see what you can find.
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Old 04-01-2014, 04:57 PM   #4
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There is information about the ABS on the Alpine Coach Tech page.
alpinecoachassociation.com
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Old 04-01-2014, 05:19 PM   #5
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Thanks for the reply!
Yes, I did an internet search with keywords; ABS, Motorhome, RV, ABS Module, ABS noise, brakes, etc., as well as combinations of those keywords and found multiple posts or articles, however, they were all specific to Volvos, BMW's, Silverado, etc.,
In several of the results I found that people described hearing a noise like a pump was running... and that their battery would go dead overnight unless they removed a fuse. The only solution that I saw offered was complete replacement.
As far as I can determine, I don't have a fuse and in order for me to get the ABS Module to quit "running", I have to disconnect one of the three connectors on the Module itself as depicted in one of the pictures I posted (I think it was the 3rd picture). The connector that I had to disconnect is on the top left of the module itself when viewed from the rear. I wish I knew where this connector went to... it has two wires that disappear into a harness. I got underneath the coach and inspected around the brake disks and hubs in the hope that I would see a disconnected ABS sensor wire or something else obvious, but I found nothing out of the ordinary.
I contacted my local repair shop yesterday, and am still waiting for feedback. I expect to be told that they will just replace the whole module, I just hope the warranty I purchased when I bought the coach will cover it.
I think I can still drive the coach as long as I plug the connector back in, but the brake pedal feels soft (mushy). And, I have to keep the engine running or be plugged in to shore power to keep the chassis batteries from draining.
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Old 04-01-2014, 05:47 PM   #6
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Equipement functions and locations vary between years, and sometimes within model year for the Alpine. To my recollection, there has been some discussion about ABS warning lights and sensor issues but few if any direct conversation about either the module between the frame rails [your pics] or the "black box" that is under the front dash, on the fire wall, near where the steering column is located. The module and the box make up the control components of the ABS on the 03s. Allegedly, there is a way to put the ABS balck box in defualt mode so that some pattern of blinking lights from the warning light on the dash will provide diagnostic codes. Unfortunately, the average RV shop probably doesnt have the tech knowledge to work this issue. You might try a light truck or school bus company--they might have the required knowledge base.
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Old 04-01-2014, 06:28 PM   #7
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Quote:
Originally Posted by JLMunsil View Post
There is information about the ABS on the Alpine Coach Tech page.
alpinecoachassociation.com
Thanks! I found some ABS maintenance manual information on the Alpine Coach Tech page as you pointed out. I missed it the first time I did a cursory look when my problem first developed. I printed it out and will see if the troubleshooting information helps.
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Old 04-01-2014, 08:25 PM   #8
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It seems like you're saying the ABS pump is running continuously. There are a few things that can make this happen. One is a fail safe mechanism that allows braking if the engine stalls or the key is off. In this situation if the brake light switch signals braking, the pump will run. Are your brake lights on?
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Old 04-02-2014, 11:16 AM   #9
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Koop- you may be blending memories of the HydroMax pump which supplies brake boost w/key Off or w/key On Engine Off. ABS provides pressure as source for modulating the brakes On/Off/On/Off... when a wheel locks up.

David- ABS is a quality feature that isn't needed for safety in driving the coach on dry or wet roads (I can't lock up my wheels under any conditions driving, and I've tried just for sport). In icy conditions, you may want to reconnect the pump to drive. If its just the pump running, then the ABS "chatter" of the brake pads isn't being engaged and you would feel that. Come to think of it, I don't know if the pump runs under ordinary circumstances w/engine running, it might (tho I doubt it, but have no evidence either way, just a hunch).

Just replacing the ABS module on a hunch isn't smart money. There is the brain (in your case located in battery box I believe) as well which might be having a brain fart. ABS has access to the diagnostic connector, IIRC the Vansco units at least have a metal toggle switch next to the front diagnostic connector (extreme bottom right of assembly of junque that is ahead of passenger's feet & behind the plastic velcro'd panel). Protocol I believe is plug in a Meritor-Wabco capable scan tool, throw switch, turn key on & have the tech do the technical hokey-pokey. So to make a short story long, you need to locate a Meritor-Wabco savvy shop that has the software & pigtail to do a reading of whuzzup.

If you haven't done so, try the Vansco shut down procedure. ABS is powered out of the Vansco stuff & the reboot maybe might alleviate a brain fart. Worth the cost of entry to give it a try.
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Old 04-02-2014, 11:45 AM   #10
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I may be mistaken, but I thought our coaches have an electro-hydraulic boost system. This provides brake boost and also provides pressure at the ABS valves when they modulate.

Key-off, step on the brake pedal. You can hear the electro-hydraulic boost pump.
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Old 04-02-2014, 12:48 PM   #11
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Koop- that's the Bosch brake system backup motor for coach-motor-not-producing hydraulic pressure. There is a mechanical pump off the drive train (yours & most Alpine's are powered off the end of the driveshaft for the air compressor; late model ULSD engine units are PTO off the trans) that produces hydraulic fluid flow/pressure to run the radiator fan, power steering & brake boost.

The ABS is an add-on system that has its own separate electric pump for a pressure source to modulate brake line pressure in case a wheel locks up. I don't know what DOT rules are but mechanically speaking you could completely disconnect the ABS & you would likely never know the difference. It'll only come into play if you lock up a wheel (which on dry or wet pavement as I've noted, I've never been able to do). On icy pavement YMMV.
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Old 04-02-2014, 01:33 PM   #12
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Thanks for the clarification Mike. Makes sense to me.

I just read the Bosch information on the ACA site - which I should have done before posting.
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Old 04-05-2014, 02:24 PM   #13
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As to the ABS light ON, I've been spelunking thru some Vansco wire loom diagrams & see that the ABS Diagnostic Switch (metal toggle type, located next to front diagnostic port for engine and labeled ABS) has only two contacts, one marked "ABS-LP_B" and the other is 1435, a known common ground. I.e. grounding ABS-LP_B activates ABS diagnostic blink codes.

Referencing: ABS Maintenance Manual, available at your local ACA Tech Library, Pin 18 of the ABS ECU is the "Blink Code" pin. It appears if that pin is grounded it will deliver Blink Codes to the ABS light. Count the blinks per instructions on p.11 of the manual & you have what the ECU believes is the issue causing light to illuminate.

It also appears from the p.11 Step II & Step V instructions, a one second "press" means send me the blink codes, and a 3+ second "press" means erase the codes. WRV used a toggle switch instead of a momentary ON push button switch. I'd try the toggle using the timing suggested by the manual, i.e. treat it like a momentary ON switch & count seconds from On to Off.
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Old 04-05-2014, 07:42 PM   #14
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EM--curious, does the one second toggle of the switch on the ABS monitoring port actually induced the short/ground and the subsequent blink codes or do you have to actually short the contact pin with the switch on? Sounds like a dumb question but the ECM on my old 87 Vette requires an actually short of two pins on the ECM port. That's why I carry a special paper clip, precisely calibrated [bent] to contact the two aforementioned pins [smile].....
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