Alarm Issue - Driving Me Crazy

[Bthrasher4]

I have an interesting problem solving question (I have checked out the TMs and have found NO resolution or information regarding this).

Almighty masters of M923A2s please guide me to the solution…

I have purchased an M923A2, which seems to be in pretty good shape. Everything functions on the truck, even the Central tire inflation System (which I am amazed it even functions).

After starting the truck and allowing the air pressure to reach its operating level (on this truck it is 120 PSI – the alarm shuts off at about 70 PSI) the low air pressure light goes out. I take off the parking brake and that light goes out and the alarm stops. I can drive the truck for about a quarter of a mile in silence (what ever that means in a 5 ton truck) and then an alarm sounds with no lights coming on in the dash area (the brake is off and all the air pressure is normal). The air pressure even stays steady when the engine is off (telling me there are no leaks in the air system - I think)

I have tried stopping the truck, shutting the engine and bleeding all the air out of the tanks and restarting the truck and letting the air pressure build again. This stops the alarm, but a little while later the alarm starts up again and runs continuously. The strange thing is, if you stop the truck and shut the engine off and turn off the ignition and battery switches the alarm continues to sound. When you bleed the tanks with the switches off or on the alarm stops sounding. Based on the TMs all the alarms should stop sounding when the battery switch is turned off.

Any ideas? Do I need to replace the low air pressure sensor, the alarm, my ear muffs, my ears? The TM seems to be silent on this kind of problem…

Your kind and wise advise would be greatly appreciated…

Thank you in adavnce

Bob Thrasher

 

[tobyS]

This is an interesting problem that would seem to be the low pressure sensor...until you mention that it stays on with the battery and ignition off. I still put my guess on the low pressure sensor. First I'd check to see if there is 24v power to the sensor with the switches off and on...and then try disconnecting it (from the electrical system) when it happens. Careful not to make a short as it is probably still live (which you check with your volt meter). If the buzzer stops when disconnected, it must not be opening the contacts correctly. If that fails, find the TM with an electrical schematic and dig deeper.

 

[Bthrasher4]

Great advice...I'll be playing with this today...

 

[tobyS]

Let me know what you find please. I'd like a switch to turn off the buzzer... as the brakes will not release with low air, so is telling me something I already know AND have red light for.

 

[Suprman]

The indicator should illuminate before the air gets so low that the brakes lock up. If you are not paying attention to the guage and your air system fails you may find yourself stuck in the middle of the road instead of off to the side. The buzzer and control of the red light are integrated remove the alarm box and no red lights either. I believe the buzzer part is on the front you can try taping over the hole or gluing it closed so the sound will be less but the warning lights will still function

 

[juanprado]

Artisan has a thread on the fail safe system. He had a bad ground. Another member here has a problem when the truck gets hot. Originally these trucks had a temp light and the buzzer is part of the circuit but most trucks have it removed early on or bypassed. I wonder if a wire from that system could be a problem. See thread by timntex.

the failsafe system seems to be plagued with lots of issues.

 

[Trailboss]

I have a similar issue and drove the truck over 3 hours home with the buzzer on when I picked it up from GL. After lots of searching and testing, I found if I jiggle the brake handle it stops. I'm guessing in my case it's the brake sensor, or something loose holding it in place. Haven't had a chance (now that I know how to stop it) to track the problem down, but it's in my round-to-it file.

 

[Bthrasher4]

Sounds like a good thing to checkout...although my issue seems to resolve it's self when I bleed out the air in the tanks, meaning this is an air/sensor issue.