Low air/parking brake buzzer inop but warning lights work

[gottaluvit]

I have the opposite problem as the original post. The alarm works flawlessly but the low air and parking brake work only sometimes. When one don't work the other don't either. When one works they both work. No problems with the high beam indicator or the front axle engaged lights. I will check grounds as mentioned. Any other suggestions?

 

[The HUlk]

I have the opposite problem as the original post. The alarm works flawlessly but the low air and parking brake work only sometimes. When one don't work the other don't either. When one works they both work. No problems with the high beam indicator or the front axle engaged lights. I will check grounds as mentioned. Any other suggestions?

Electrical Engineer here, The failsafe I have is a green plastic housing which I know has a circuit board, components, relays, and the like. At least a digital 555 timer IC circuit for the buzzer and lamp oscillation. They filled it after assembly with black epoxy resin so it's very difficult to diagnose a failure. They can go completely out like mine was when I got the truck. When they are completely out the buzzer, parking brake, low air lamps were inoperational . On a failsafe unit that is somewhat operational a variety of unusual behavior could occur. I have seen soldered boards come back after years in the automotive field and stuff happens. Heat cycling causing solder joints to microfracture and induce mechanical creep due to varying thermal coefficients of the materials involved. The highbeam indicator will still work if the failsafe is removed or broken, it does not have to do with the failsafe box. The front axle IN indicator will also still work if the failsafe is removed or broken, it also does not have to do with the failsafe box. Also the failsafe box wiring connector has a ground loop on it. I placed it on one of the box mounting bolts with those star washers that bite in to get a good electric contact. I did notice the buzzer got quieter when the ground wasn't grounded and I would guess that without this ground properly connected, excess electrical stress may occur on some of the failsafe box circuit board which may have a serious effect on life expectancy based on my experience.

 

[gottaluvit]

Electrical Engineer here, The failsafe I have is a green plastic housing which I know has a circuit board, components, relays, and the like. At least a digital 555 timer IC circuit for the buzzer and lamp oscillation. They filled it after assembly with black epoxy resin so it's very difficult to diagnose a failure. They can go completely out like mine was when I got the truck. When they are completely out the buzzer, parking brake, low air, and front drive IN lamps were inoperational. On a failsafe unit that is somewhat operational a variety of unusual behavior could occur. I have seen soldered boards come back after years in the automotive field and stuff happens. Heat cycling causing solder joints to microfracture and induce mechanical creep due to varying thermal coefficients of the materials involved. The highbeam indicator will still work even if the failsafe is removed, it does not have to do with the failsafe box. Also the failsafe box wiring connector has a ground loop on it. I placed it on one of the box mounting bolts with those star washers that bite in to get a good electric contact. I did notice the buzzer got quieter when the ground wasn't grounded and I would guess that without this ground properly connected, excess electrical stress may occur on some of the failsafe box circuit board which may have a serious effect on life expectancy based on my experience.

Hey, that makes sense considering the alarm has volume and tone variables. I guess I will focus on it's ground and if it still messes up look for a new box. Thank you.

 

[The HUlk]

Hey, that makes sense considering the alarm has volume and tone variables. I guess I will focus on it's ground and if it still messes up look for a new box. Thank you.

Glad this info is helpful.

One thing I failed to mention is that on mine, when the ground is properly connected, I hear a lower volume buzzer when just the parking brake is set and the parking brake lamp is flashing, and the volume will increase for a low air alarm when that lamp begins...flashing I believe.

 

[gottaluvit]

Glad this info is helpful.

One thing I failed to mention is that on mine, when the ground is properly connected, I hear a lower volume buzzer when just the parking brake is set and the parking brake lamp is flashing, and the volume will increase for a low air alarm when that lamp begins...flashing I believe.

Well, that would be nice. My volume tone differences are just random and rapid. Thought it was my hearing at first as it is a bit off too, but after reading your post I suppose it might not just be me.

Jim

 

[Artisan]

GUYS, it is flat out STUPID to kill that warning device.
FWCD = Failsafe Warning Control Device . IdahoMotorpool
sells the new style cheap and if $100 is too expensive for
you then you really should consider selling your truck.

It is there for a REASON. There is a simple work around if
you hate waiting for your truck to build air pressure.

Simply get a GLADHAND and mount an air Chuck nipple to
the end w/ a VALVE in-between. (See pic below) Before you start your truck
you make SURE wheels are chocked and P-Brake is ON and
connect an air line to the DS front Gladhand on your truck and fillerup.

One minute or so later and your tanks are topped off, you disconnect
your air fill valve and start the engine and off you go. (Be sure to
be SMART and open the gladhand valve ON your truck prior and
remember to close it after you fill. The PS gladhand is always
vented w/ NO VALVE in front, look at it, you will see.)

Dollars to donuts the guys who kill these devices are pennyless and
do not own property and never will. Play ball the RIGHT way, do
it wrong and if you ever do own property and you get caught
w/ a bypassed FWCW while in a wreck and you could lose it all! This is a ligating
society and YOU CAN BE SUED for not keeping your truck roadworthy.


It is usually the FWCW that goes bad but you will be smart to replace
both sensors at both air tanks on the PS AND BE SURE TO PULL THE
GROUND AND CLEAN ALL SURFACES USING A PROPER INTERNAL/EXTERNAL
STAR WASHER . I think it was a #55 wire.

 

[Bandit02]

My FWCD is acting up too. Buzzer goes 24/7 with power on and no park brake & low air warning lights at all. Imma start this week some time cleaning the grounds and start the diagnosis first before condemning it.

 

[98G]

If the buzzer is the first notice you get that there's a low air pressure problem then you're not watching your gauges closely enough...

If you can hear the buzzer at highway speeds in one of these trucks then you hear a lot better than me... (plausible)

 

[Bandit02]

I've ran with it unplugged since the day I bought it, it's the only issue this truck has.

I've contemplated very much making my own alarm box but I need some more info on what wire does what going in/out the box. I watch my gauges (I have my CDL) so driving a heavy truck isn't unfamiliar to me.

 

[The HUlk]

I'll draw you up a diagram to make your own FS box, stay tuned...

 

[Bandit02]

I'll draw you up a diagram to make your own FS box, stay tuned...

Thanks, I appreciate that.

Hopefully, inside the box there is a wee bit of excess wiring on the plug, like to keep the plug OEM if possible.

 

[The HUlk]

Thanks, I appreciate that.

Hopefully, inside the box there is a wee bit of excess wiring on the plug, like to keep the plug OEM if possible.

On the boxes I have seen with the black epoxy, you would be lucky to extract anything from that. That stuff is as hard as a rock and takes weeks to dissolve and by then the plastic, etc. is destroyed. I used to inspect automotive sensor failures using that method. I'm sure you can order a matching mil spec connector from the big mail order electronics distributors like Allied, Newark, Mouser, etc.

Here is a CONCEPT diagram and it is UNTESTED, USE AT YOUR OWN RISK.

I honestly probably will not build one of these, but I hope it helps someone else who wants to.

-The warning lamps would come on solid with this design. An additional flasher circuit would need to be added to each lamp's output signal for flashing warning lamps.

View attachment m939 fscircuit.pdf

 

[Bandit02]

That's awesome!

 

[gottaluvit]

Well, that would be nice. My volume tone differences are just random and rapid. Thought it was my hearing at first as it is a bit off too, but after reading your post I suppose it might not just be me.

Jim

Well, I assume it was the ground on the control box as lights have been working normal since messing with them. The audible differences I heard were indeed my hearing as when I turned my head back and forth the tones volume and tone changed as doing so. That tone is an odd one as I cant even hear it when outside on passenger side of truck but can hear it in my house 100 yards away (on driver's side).

 

[EO2NMCB]

For every one saying it is the law that you have a buzzer, maybe you should look up FMSCA 393.51 it is either or.

(2) A warning signal that is audible or visible to a person in the normal driving position and provides a continuous warning to the driver whenever the air pressure in the service reservoir system is at 379 kPa (55 psi) and below, or one-half of the compressor governor cutout pressure, whichever is less

 

[Bandit02]

In Canada (for me). You need to have a low air light for vehicles manufactured after a certain year. You can be deaf and drive a truck but obviously not blind so a light is preferred but they come equipped with both from OEM.