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LMTV Abs troubleshooting

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Berend

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Hello

I have a 2001 M1078A1 where the abs light stays on. Does anyone know how to troubleshoot the abs or read the abs codes ?
 
Suprman

Suprman

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On the c7 you might be able to read abs codes with a heavy truck reader. 3126 not sure there may be a separate diag port for it. The module by the air/hyd pump. I think there is a breaker for it in the panel.
 
snowtrac nome

snowtrac nome

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I never had any abs issues on the trucks in Iraq. the system is about the same as commercial trucks you will need the wabco software and a code reader like a prolink than you can hool into the same dutch plug that is used for the engine or transmission.
 
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Berend

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One of my rear brake chambers is leaking air, could that trigger the abs light? I did a brake test but even with the abs light on it still works.
 
Suprman

Suprman

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It shouldnt. It could just be a stored error that will self clear over time. There are wheel sensors that detect slip, some valves on the frame rail and the brain behind the cab.
 
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Berend

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When I disconnect my CTIS Controller the abs light go’s out. Switched to another CTIS controller and abs light stays off.
 
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charlesrg

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Bernard, do you think your previous CTIS controller was defective ? I was just testing another CTIS controller today and had the same issue. ABS light would come on on the new controller.
 
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Berend

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Yes I think so, but could also be there was a green controller instead of the black one. Can’t remember anymore. If you put a green controller in a A1 truck you get all sorts of faults in the ctis and Abs.
 
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Ronmar

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The ABS fault disappearing when CTIS is unplugged indicates to me that it is probably a programming conflict. The CTIS is connected to the ABS, trans and engine controllers via the J1939 and J1587 data busses. I don’t think there is any actual or planned interaction with CTIS, they simply did it so it was one stop shopping for any programming, access and diagnosis...

If the ABS fault appeared when you plugged in CTIS, then it is probably a version or programming incompatibility, or there is a fault in that CTIS.
If it all of a sudden popped the ABS fault without you doing anything with CTIS, then perhaps it is some failure in the CTIS effecting comms on one of the data busses that the ABS controller is sensitive to.

You need to read the codes to see exactly what it is...

Or, you could disconnect the data buss connections in the CTIS connector and go on with your life as the CTIS operates independently other than receiving a speed signal and driving the overspeed warning light, which it accomplishes directly with hardwired signals with out need of the data busses...
 
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charlesrg

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Ronmar said:
The ABS fault disappearing when CTIS is unplugged indicates to me that it is probably a programming conflict. The CTIS is connected to the ABS, trans and engine controllers via the J1939 and J1587 data busses. I don’t think there is any actual or planned interaction with CTIS, they simply did it so it was one stop shopping for any programming, access and diagnosis...

If the ABS fault appeared when you plugged in CTIS, then it is probably a version or programming incompatibility, or there is a fault in that CTIS.
If it all of a sudden popped the ABS fault without you doing anything with CTIS, then perhaps it is some failure in the CTIS effecting comms on one of the data busses that the ABS controller is sensitive to.

You need to read the codes to see exactly what it is...

Or, you could disconnect the data buss connections in the CTIS connector and go on with your life as the CTIS operates independently other than receiving a speed signal and driving the overspeed warning light, which it accomplishes directly with hardwired signals with out need of the data busses...
Click to expand...
Thank you very much. I will try to troubleshoot and post my findings. With my old controller I had no ABS light so it comes on everytime I put the replacement. So I decided to just stay with my old one.
 
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gslader

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Paging @Ronmar : Reviving this thread to ask a different question. I have a 2003 M1078A1. Today I was backing up a steep icy driveway with chains on the rear wheels in “mode” (locked differential). There was a little bit of wheel slip and when I got to the top I noticed my ABS light was on. I was parking my rig for the night so I didn’t have a chance to see if the light cleared on its own. I did check all the rear airlines to see if I could see any signs of the chains interfering with the airlines or sensor wires and they all looked pristine. Could it just be that the ABS system was picking up the wheel slippage and will self clear in the future?
 
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GeneralDisorder

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gslader said:
Paging @Ronmar : Reviving this thread to ask a different question. I have a 2003 M1078A1. Today I was backing up a steep icy driveway with chains on the rear wheels in “mode” (locked differential). There was a little bit of wheel slip and when I got to the top I noticed my ABS light was on. I was parking my rig for the night so I didn’t have a chance to see if the light cleared on its own. I did check all the rear airlines to see if I could see any signs of the chains interfering with the airlines or sensor wires and they all looked pristine. Could it just be that the ABS system was picking up the wheel slippage and will self clear in the future?
Click to expand...
Many ABS systems will complain if they see differing wheel speeds and the codes will typically self clear. It could be the case on these as well. We have that problem a lot at my shop working on vehicles when we run them on a lift and wheel speeds are all over the place so the controller just freaks out and throws codes. Usually you drive them on the street a bit and they will self clear or we sometimes reset them manually before we return the car to the owner.

Again - I DO NOT know this to the case here but as the Wabco system is basically the same as over-the-road trucks it wouldn't surprise me at all.
 
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Ronmar

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Yea what General said would not surprise me at all. ABS/Traction control vehicles occasionally do this, and from what I have seen of the LMTV ABS wiring, the system looks like it could be capabel of traction control, but the LMtV does not have the air supply plumbing to the actuators... if nothing was damaged, i suspect it will clear with normal driving…
 
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gslader

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Just to close the loop on my ABS issue. I started my truck the day after the ABS light came on and let it warm up for about 15 minutes - it stayed on the whole time. I then started driving it an after about 5 minutes the ABS light self cleared and stayed off. I’ve driven it 4 or 5 times since then and the ABS light has not come back on. Thanks to all that helped with guidance on this.
 
hawk-aggie

hawk-aggie

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Can't help or advise on the OP, but have a question.

Have a 2002 1078A1 with the ABS indicator on. Had other issues as well. Fixed those, but still have this ABS issue. Don't have any diagnostic tools, but may see if the local Army Reserve guys will help in that respect. In the meantime, I decided to test the brakes. Got up to 20 mph driving across our gravel parking lot, hit the brakes, and the rear brakes locked up - the left more than the right as evidenced by the skid marks. Felt a little pumping in the front brakes, so some of the system seems to be working to a degree. Any of you more-experienced-than-me guys have a notion where to start with a fix? Thanks.
 
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aw113sgte

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Still having lots of issues talking to my ABS. Inspect of the module itself and there was a lot of corrosion on it cleaned all the pins up and retried but still didn't work.
Unplug the ABS entirely but still getting that j 1587 fault code. Also I'm showing a PGN 65226 from ECU, but connecting to the ECU with CAD ET shows no fault code and there's no fault code in the DG technologies fault tab.
The side of the ABS says it's J1939 so I wouldn't think the 1587 fault would affect that? But looking at the wiring diagram it does have both buses connected to the ABS ECU
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