M925A2 Electrical issue, Circuit breaker/relay issues, Horn/ABS problems

[acolesurf]

Hey there everybody, I just recently purchased a M925A2, and have been having some fun with it, but now i've run into a problem...

While driving, my dog was sitting next to me, and when I hit the brakes, he started to slide off the seat, and braced himself by putting his paw on the dash. This is where the problem begins, he turned off the battery switch while the truck was still running. Next thing I saw were some blue sparks/electrical bursts coming from under the dash by the wires that only lasted about 1 second, and I immediately turned off the engine switch too. So then everything is shut off, I go to restart the truck, it starts up, but I am having some problems with some electronics now.

First, the air horn started sounding continuously, there is constant power to the air solenoid going to the horn under the hood, even when I unplug the power from the switch at the bottom of the steering column.

Next, the ABS light now stays on constantly. It used to go off once the truck was started, but now it stays on.

Other then that, I inspected all the wiring under the dash to try and see where the sparks came from, or if some wires melted together and are causing the short, but I can't seem to see anything. I checked both the fuses under the dash, the 15amp one was burned out, so I replaced it, but it did not change the symptoms. From looking through the TM, and the troubleshooting guide, I am wondering if the circuit breaker 10 is malfunctioning? but through the troubleshooting guide for the horn, it really only works through the issue of the horn not sounding at all, not the issue of the horn sounding all the time. As for the ABS, is there an ABS module that could be fried?

Thanks for all the help!!!

 

[simp5782]

Hey there everybody, I just recently purchased a M925A2, and have been having some fun with it, but now i've run into a problem...

While driving, my dog was sitting next to me, and when I hit the brakes, he started to slide off the seat, and braced himself by putting his paw on the dash. This is where the problem begins, he turned off the battery switch while the truck was still running. Next thing I saw were some blue sparks/electrical bursts coming from under the dash by the wires that only lasted about 1 second, and I immediately turned off the engine switch too. So then everything is shut off, I go to restart the truck, it starts up, but I am having some problems with some electronics now.

First, the air horn started sounding continuously, there is constant power to the air solenoid going to the horn under the hood, even when I unplug the power from the switch at the bottom of the steering column.

Next, the ABS light now stays on constantly. It used to go off once the truck was started, but now it stays on.

Other then that, I inspected all the wiring under the dash to try and see where the sparks came from, or if some wires melted together and are causing the short, but I can't seem to see anything. I checked both the fuses under the dash, the 15amp one was burned out, so I replaced it, but it did not change the symptoms. From looking through the TM, and the troubleshooting guide, I am wondering if the circuit breaker 10 is malfunctioning? but through the troubleshooting guide for the horn, it really only works through the issue of the horn not sounding at all, not the issue of the horn sounding all the time. As for the ABS, is there an ABS module that could be fried?

Thanks for all the help!!!

Go to the 5 ton TM section and download the P2P program so it will help you track down wires.

The ABS modules are between the rear axles mounted up high. There is one for each axle.

The horn should have power all the time with the switch on. It is ground side switched thru the steering column to activate. So that wire is grounded out somewhere OR it just simply is stuck in the ground position and just keeps on sounding. It is a bad solenoid. That is common. You see lots of trucks that have been sitting with unplugged or piped off horns.

The abs light could be a blown solenoid in the PCB box that controls the ABS or the diodes but generally it blows the whole thing via the alternator shorting out. I don't see how turning off the top switch first caused sparks unless there are some exposed wires. The switch should have been locked with the tit so it can't move As far as turning the top switch off first I have done it several times not thinking and just killing a truck.

 

[acolesurf]

Thanks for the info. I seemed to have opened a can of worms, because now the CTIS is also acting up, I hear the system start making noise in the cab, like it wants to add pressure to the tires, but no air pressure is leaving the air tank like before. And the airline from the compressor going into the air filter box before the air tank is making a weird clicking noise constantly. I think what happened is an over voltage senario, turned off the battery switch, and voltage gauge jumped into the red. So I think the over voltage might have cooked some solenoids or something. Hopefully it is just a ground issue somewhere that once it is not grounded, everything will go back to normal. Is the PCB box that controls the ABS the boxes you were talking about above the axles? Could these be not letting air into the tires? Thanks for all the help, and I am scouring through the TM's trying to find solutions too.

 

[acolesurf]

Also I tried running the P2P program, but i'm stuck on a mac, so i'm going to have to work on a work around to get that running.

 

[simp5782]

Thanks for the info. I seemed to have opened a can of worms, because now the CTIS is also acting up, I hear the system start making noise in the cab, like it wants to add pressure to the tires, but no air pressure is leaving the air tank like before. And the airline from the compressor going into the air filter box before the air tank is making a weird clicking noise constantly. I think what happened is an over voltage senario, turned off the battery switch, and voltage gauge jumped into the red. So I think the over voltage might have cooked some solenoids or something. Hopefully it is just a ground issue somewhere that once it is not grounded, everything will go back to normal. Is the PCB box that controls the ABS the boxes you were talking about above the axles? Could these be not letting air into the tires? Thanks for all the help, and I am scouring through the TM's trying to find solutions too.

The PCB box is mounted on your firewall just above the steering shaft. It contains two solenoids. Search "PCB box" in the 5 ton section and you will see what it looks like. The ABS modules are separate and are located above the axles. Does your voltage gauge show that you are charging or no?

The clicking noise from your air line into your air dryer is normal that is how you know that it is working. Unplug the CTIS for now. That could be a totally seperate problem and tackle one thing at a time. The ABS is separate from the CTIS system except for probably on how it gets it's power.

Crack open the PCB box and see if the solenoids or diodes appear to be fried. The TM's are virtually useless in an electrical element.

You said you have replaced the fuses. That one that had the blown fuse {15amp)is a good place to start your tracing of wires and components. That 15amp fuse goes from the dash directly to the ABS main module which is located behind the front axle tandem. It is a bigger unit that the one for the rear axle.. Be sure you have power to that 15amp fuse. Just cause it blew doesn't mean it protected what is in front of it which is a PCB box. It does not go thru the circuit breakers on that wire to the ABS. You are looking for wire tag # 10. It will be a main wire with power.

The 3amp fuse is wire # 54. This should be yellow in that little pigtail harness that supplies power to the light. So you know that it is working. The purple wire in that harness gets the incoming "fault message" in the form of power from the ABS module.

If you have power on that 15amp fuse in the dash then I would suspect a blown ABS module.

Member suprman has new ABS modules. You can email him at will @ pawnking . com

 

[acolesurf]

Wow, thanks for all that, I’m looking into the PCB now, then the abs modules. My alternator does show charging when the truck is running.


Sent from my iPhone using Tapatalk

 

[simp5782]

Wow, thanks for all that, I’m looking into the PCB now, then the abs modules. My alternator does show charging when the truck is running.


Sent from my iPhone using Tapatalk

That is good that it is. For future reference you may want to get in touch with member 74M35A2, he sells a brushless alternator for the A2 trucks that gets the PCB and ABS modules out of the equation. Alot of these trucks will have a voltage spike and it will blow the PCB box and ABS module together resulting in no abs and a no start problem for the truck. His alternator will fix that problem before it happens. Or another Chinese clone will work. There are several threads on that.

If you have power at that 15amp fuse then your pcb is probably good. As the power from your battery/starter goes thru the PCB after coming from the main dash power switch. It then goes back thu that 15amp fuse to the other items. If you say you have power at your horn solenoid then the PCB is good. Power goes thru the horn as well off the #10 wire that the 15amp fuse runs.

There is some ABS diagnostic procedures. https://www.steelsoldiers.com/showthread.php?79389-M923A1-Abs-Light

 

[acolesurf]

Well crap... I pulled the PCB board off, realized I couldn't get in the thing without cutting it open. So I was going to try your last advice and check out that fuse power. I reinstalled the PCB, then fired up the engine and checked the voltage at the fuse, which was blown again. It was reading 37v... Then I looked at the voltage gauge and it was showing in the red. So there is power at the fuse, but since the fuse was blown, i guess there's a short after the fuse. Also, since the alternator is overcharging the system, does this mean the PCB is bad? Or a voltage regulator somewhere that is bad?

 

[acolesurf]

I know the system wasn't charging before I pulled the PCB off, so maybe I messed something up when I did.

 

[porkysplace]

I know the system wasn't charging before I pulled the PCB off, so maybe I messed something up when I did.

Did you unhook the batteries before you tried to take the PCB off ?

 

[acolesurf]

No I did not...


Sent from my iPhone using Tapatalk

 

[porkysplace]

No I did not...


Sent from my iPhone using Tapatalk

Rule 1 of working electrical is to disconnect the batteries. That said since you now have a overcharging problem
A power spike probably fried the voltage regulator.

 

[simp5782]

More than likely your alternator was on the fritz end of the whole scenario anyway with the dash short. With that PCB box they are pretty susceptible to any short or spark and they tweek out. Alot of people have issues with those alternators like I said earlier. I ran one for 60,000 miles without issue and it had every condiment under the hood poured on it. I guess the rest just don't last.
If you replace your alternator with the an updated one the PCB box goes away from the equation. as the alternator is a single wire system. You can also upgrade to a newer starter that does not need the solenoid in the PCB box as well.

So at this time. Let's isolate your system. Remove the ground wire from your alternator. Should be under the cover on it and leave it off. Reinstall the 15amp fuse and see if it blows. If it does you need to find out which end of the circuit it is coming from the PCB or the ABS module or is it back feeding from the horn/spring brake pressure switch. So since you are having the horn issue. start by removing that from the solenoid on the horn then put a fuse in. If it doesnt pop then you know where an issue is. if it does move on down the list.

What I do is a I have 2 pig tails. both are Inline fuse holder wires with a female connector and one with a male connector so I can tap into the different connectors if there is a short. basically plug each inline into each end of that circuit and see which one blows the fuse on that pigtail holder. Hope that makes sense. basically you are isolating the system before or after the fuse. More than likely it will come from the PCB end.

 

[simp5782]

No I did not...


Sent from my iPhone using Tapatalk

That generally doesn't hurt em. I unplug em all the time with the trucks running especially on one that has stupid wiring splices and crap or a harness that has been turned into a birds nest. You didn't do anything wrong. I have one I am working on now that will charge into the red every so often. then back into the green. It is on its way out as well.


You can rebuild your PCB box pretty cheap. Both solenoids are on ebay. search cole harsee 24063. It is always good to have some spare parts.

 

[acolesurf]

So I went back this morning and started troubleshooting. The alternator this morning was performing fine, in the middle of the green, so I didn't mess with it for now. But I did order the new delco alternator, J180 short bracket, "used" PCB box, and am currently working on a ABS module, so I will have backups for all.

At the 15amp fuse, the non-supply side is completely grounded, I traced that wire to the rear ABS module, unplugged the big connector, and the short went away, I can install the 15amp fuse now without blowing it. But does that mean that the rear ABS module is bad? Or do some of those wires feed to the front ABS module where the short could be farther downstream? I am going to try to unplug the front ABS module and plug in the rear one, and try to keep moving downstream until the short appears again, then hopefully I will have isolated the problem.

The thing that is weird to me, is that I was hoping that the horn air solenoid would stop going off once I cut out the short, but it is still going, even if I unplug the wire at the base of the steering column. That is why I believe the short is coming from somewhere else where it could be interfering with both, which hopefully means the ABS module is actually .

 

[simp5782]

So I went back this morning and started troubleshooting. The alternator this morning was performing fine, in the middle of the green, so I didn't mess with it for now. But I did order the new delco alternator, J180 short bracket, "used" PCB box, and am currently working on a ABS module, so I will have backups for all.

At the 15amp fuse, the non-supply side is completely grounded, I traced that wire to the rear ABS module, unplugged the big connector, and the short went away, I can install the 15amp fuse now without blowing it. But does that mean that the rear ABS module is bad? Or do some of those wires feed to the front ABS module where the short could be farther downstream? I am going to try to unplug the front ABS module and plug in the rear one, and try to keep moving downstream until the short appears again, then hopefully I will have isolated the problem.

The thing that is weird to me, is that I was hoping that the horn air solenoid would stop going off once I cut out the short, but it is still going, even if I unplug the wire at the base of the steering column. That is why I believe the short is coming from somewhere else where it could be interfering with both, which hopefully means the ABS module is actually .

The horn is ground side switched from the steering column. if you unhook the ground wire off the solenoid (#25) on the horn does the horn turn off? It should always have power with the key on. It is the same power from the #10 wire the 15amp fuse line. There is a diode in that harness but that should not cause a problem.

More than likely it is the front abs module.

 

[acolesurf]

The horn is still sounding even with no 15amp fuse, and the ground at the base of the steering column unhooked. But does not sound when #25 is unhooked.


Sent from my iPhone using Tapatalk

 

[acolesurf]

This is probably a stupid question, but where is the front and module? I can’t find it...


Sent from my iPhone using Tapatalk

 

[acolesurf]

Abs* module


Sent from my iPhone using Tapatalk

 

[acolesurf]

Never mind, I’m an idiot, I was thinking front wheels had a abs unit too


Sent from my iPhone using Tapatalk