Community Forums

Pull · 02-20-2023, 11:34 AM

Hi Folks,

2000 Holiday Rambler Ambassador, Allison 1000 trans, Cummins ISB260, Roadmaster chassis

I noticed my chassis batteries suddenly going dead (new batteries a few months old) and after charging them up I attempted to move the coach. A check trans light, ABS light, and Alt charge lights were on. I determined the problem at that time was a bad alternator and have replaced the original "Dixie" 165 watt alternator (they no longer make these and apparently they cannot be rebuilt) with a Delco Remy 200 watt alternator. The alternator swap went fine and I am getting a charge on the batteries again; however, I still have an ABS light on and the coach appears to be in limp mode. The transmission goes into reverse and drive (it is very jarring when it goes into gear) but does not actually shift. It seems that it is stuck in 2nd or 3rd gear and will only go about 30 mph or so (not sure as the speedometer is now not working as well). I believe my issue with the transmission will be resolved if I can correct the ABS light (please correct me if my assumption is wrong) and as such I've cleaned all of the wheel sensors and took the coach for a short drive with no changes. Any pointers on how to confirm the wheel sensors are working with a multi meter?

I also pulled the connectors out of the ABS ECU and cleaned them with electrical cleaner (they were clean to begin with) and no changes.

I do not have an ABS board with a reset button like so many others have alluded to and I am now stuck. Any and all pointers welcome - looking for some ideas.

Any suggestions on a scan tool that is a reasonable cost and where I might find an ABS service port to read codes (there are a few round connectors that I have located and I'm not sure what they are for)? It is a Meritor Wabco ABS unit from what I can gather.

Thanks!

MrMark52 · 02-20-2023, 04:00 PM

Am wondering if you might be having a grounding problem.

Our ‘02 Workhorse gas chassis with Allison transmission - the day I picked it up to drive home, got an ABS light. No issues with driveability.
Found out the only way to read the ABS module was with a dealer reader.
Then found out that both brake recalls had not been implemented.
Then found a dealer 90 miles away who would do the recall work. Had him read the ABS codes - he said likely the left front wheel sensor and the master cylinder was bad.

Only way to fix the master cylinder was replace. And he both knew and was nice enough to say “change the sensor, the light will probably go off as we left the MC plug disconnected”.

I drove the coach for a year before I finally replaced the left front wheel ABS sensor - barely got out of the driveway before the ABS light went off.

Drove the coach 5k-8k miles with the ABS light on, no issues.

Now I have ABS, and a disconnected plug on the MC.

FWIW - the disconnected plug - in someone’s infinite wisdom of master cylinder design - they designed the front/rear pressure imbalance system in the master cylinder so it cannot be repaired (or rebuilt).
New MC is ~$350.00.
Our sensor plug is still unplugged.
Our ABS light is still off.

Pull · 02-20-2023, 04:40 PM

Thanks for the idea MrMark52, I'll give this a try. I'm fine without ABS as long as I can get the transmission back to normal operation.

MrMark52 · 02-20-2023, 05:39 PM

And FWIW (and I don’t have a link to it) - but you can find resistance specs for the sensor.

On our coach - I bought 2 as they are identical front left and right. But I only replaced the suspect one - it worked - I didn’t proceed and now have a spare sensor, just in case (I don’t remember if the rear’s are the same - but at the moment, don’t care - will cross that bridge when I get to it).

Pull · 03-18-2023, 11:22 AM

Sorry for the late reply, finally got around to unplugging the MC. Took it for a drive and the ABS light is still on. I guess the next thing to try is to test the wheel sensors or find someone that can read the ABS code. If anybody knows of a code reader that will work that is a reasonable cost, please let me know.

Pull · 03-18-2023, 12:56 PM

I’ve just tested all of the wheel sensors and 3 of them are at 1.172k/ohm while the fourth is at 1.189k/ohm. I think I might replace this one to see if it is the problem. I can’t seem to find anyone local that would be able to read the ABS code and driving anywhere far at 30mph does not sound like a good idea.

MrMark52 · 03-18-2023, 01:17 PM

While I don’t really know, but I don’t think fixing the ABS issue will solve the limp mode problem. But always good to fix.

This might help you for the ABS issue - https://www.bendixvrc.com/itemDispla...ocumentID=6115

You might see if there is a way to get blink (diagnostic) codes for the engine, either that or find a code scanner for your engine.
Probably won’t help you with the ABS, but between that and the link above, you may have enough info to ferret out what I think are different issues with the coach.

Pull · 03-18-2023, 01:55 PM

The ABS system is Merator Wabco on this coach, but thanks for the link anyway. Unfortunately, there is not an LED on this coach for blink codes (or a reset button).

I'm going to continue down the path of replacing one wheel sensor and also I have read that replacing a fuel filter might also solve the problem. From what I've read in other forums, Monaco took a shortcut on some coaches and utilized the ABS light for a bad fuel filter... sounds crazy but I guess it is worth a shot.

Pull · 03-25-2023, 03:31 PM

After replacing both fuel filters and the one wheel sensor, the abs light is still on and the transmission is still in limp mode.

MrMark52 · 03-26-2023, 07:29 AM

Try this - on the Master Cylinder - the front/rear brake fluid pressure differential pressure is measured via the sensor mounted to the MC. Unplug it.

All that sensor is is a Normally Open switch that the plunger rides in a depression ground into a rod; the rod has hydraulic pressure from the front and rear hydraulic systems applied, one applied to each end. If there is a differential pressure between the two systems, it pushes the rod left or right which the pushes the switch plunger and energizes the switch, and turns on the light.
That rod will stick - mine did. As a NO switch, all that switch does is close and send a ground signal to the ABS computer that there is (or was) a differential pressure between the two hydraulic systems.
Differential pressures can occur in a hydraulic system, like when hitting the brake rapidly.

The design used by Workhorse and whoever made the brake system monitor system for them is a poor design as the only way to fix it is to replace the MC. I’ve yet to find a rebuild kit for the MC, and to access and remove the rod (to clean it up of brake gunk and rust) hydraulic fluid bleeds out. And once you do access, getting a stuck rod out appears to be quite difficult.

So - try unplugging that sensor and see if it solves your ABS light issue. When ours did it - the coach Tran fine with the ABS light on for over a year, and it has continued to run fine for another year with the sensor unplugged.

I don’t know much about diesel - but would suggest that you either get a scanner to look for thrown engine codes, or limp the coach to a service center that can work on Workhorse and get them to read codes for you, both engine and ABS.

FWIW - there are no codes thrown (that I know of) that will tell you if the pressure differential switch is the issue. Easiest to just “unplug” the sensor.

A service center can read the codes for the ABS and tell which sensor is the issue. And since you’ve already replaced the two front, maybe go ahead and replace the 2 rear (process of elimination).
FWIW - when I replaced our faulty ABS sensor, I barley had the coach out of the driveway before the ABS light went off.

Pull · 03-27-2023, 05:19 PM

Thanks for the info MrMark52. I unplugged the sensor on the MC and took a drive. The ABS light is still on and the trans is still in limp mode. I just got off the phone with Wabco tech support to get their take on things as well as have them refer me to the nearest service center. Wabco confirmed that with the with the ABS light on, it will definitely put the transmission into limp mode. His unofficial advice was to unplug the ABS in order to get the transmission out of limp mode, so that is my next course of action. Crawling down the highway to the service center to get the codes read just doesn't seem safe, so I'm hoping this will allow the trans to function normal again.

MrMark52 · 03-27-2023, 06:19 PM

Totally agree with you on limp mode traveling.

Like I said, I drove our coach for a year or so without ABS - and fortunately it didn’t activate limp mode. But then we’re gas.

Must be something about diesel that they limp mode the engine.

Arch Hoagland · 03-27-2023, 06:36 PM

Have you checked the transmission fluid level?

The Allison 1000 came with Dexron III in those years and was supposed to be changed every 25,000 miles or two years. The spin on filter should have been changed too.

I recently went to Transynd on the last change. I do my own fluid changes.

MrMark52 · 03-27-2023, 07:03 PM

Changing to TranSyn is a great idea! Did it to mine as well - and the next morning, there was a dozen roses, a box of chocolates, and a bottle of wine waiting for me on the steps.

But I’m thinking that isn’t the OP’s issue.