AM General M934/A0/1 With ABS MWO - Dash Warning Light Burning Bright!!!

[archmark]

The ABS dash warning light on my AM General M934/A0/1 has started burning constantly. Previously it worked as it was supposed to during dry, hot weather, extinguishing after the start up check, and then intermittently during cold, wet weather, sometimes extinguishing after startup and sometimes not. Now it stays on constantly, no matter what the weather. It took a few years of progressively getting worse before it got to this point.

Of the probable long troubleshooting list of things to check, what's number one on the list (and everything else too please!) that I need to troubleshoot? Hopefully it's mostly "plug & play".

Thanks for all the help. Having no ABS in a 5 ton on wet roads does kinda concern me...

Mark

 

[simp5782]

With the upper switch on then the lower switch on is the ABS module conducting it's self test? The 2 clicks? before you start it. Just behind the dash light there is a 5amp fuse holder that goes to it and a few other colored wires. Check it to make sure it is not blown.

If it is not blown then you need to visually inspect the ABS harness, modules, and wheel sensors to ensure that something isn't damaged before you start trouble shooting.

If nothing is obvious pop open your PCB box on the firewall and take your test light or volt meter and check that you have 24v or atleast power on the drivers side large post of the UPPER solenoid. If you don't then check the opposite side of the post. If you have power on the passengers side of that port then you have a bad solenoid more than likely. Simply check the power coming off the green wire going to the lower connector with the battery switch and starter switch up but the truck not running.

If the solenoid is testing fine then you have a bad ABS module more than likely. Shutting the truck down in the wrong order can cause this as well as not letting it complete its self test.

No ABS in a 934 is not a big deal. They skid and wheel hop really bad in the cargo trucks and tractors with no rear weight. The 934 having the huge box on it is an advantage on braking on the rear axles with or without abs.

 

[98G]

Or weak batteries may be your only problem.

The ABS is very voltage sensitive. Just because it spins that 14 liter engine doesn't mean its enough to appease the ABS light....

 

[jonesal]

Or weak batteries may be your only problem.
The ABS is very voltage sensitive. Just because it spins that 14 liter engine doesn't mean its enough to appease the ABS light....

This is great advice. Because it happened to me!

Al Jones
Brookings, SD

 

[74M35A2]

What does your volt gauge show during running?

 

[jonesal]

What does your volt gauge show during running?

I assume you are NOT referring to the on-board volt gauge. Those things.... Use something you can believe like a volt meter. When I had issues with my ABS, I searched all the threads and the most common problem was a harness issue that were fixed by simply detaching connectors and reattaching. There's a bunch of them, just a dirty or corroded connection, which of course includes grounds and batteries. The Midland code reader in conjunction with the Point to Point software will tell you right away where your problem is if you have access to one.

Good luck!

Al Jones
Brookings, SD
M923

 

[74M35A2]

Plenty of threads here where the ABS light came on, then driver observes volt gauge pegged in red zone. Also several where the alternator would over-volt sporatically or temp related, until it finally went full-tilt full time.

On this one I would suspect an alternator going out to lunch. We’ll see... I think there are 2 fuses under the driver side dash to check.