Air pressure light and alarm won't turn off

[captcarc]

Hello. A minor, but noisy, new issue just popped up on my M934. Even after primary and secondary air pressures build well past 60psi, the air pressure light and buzzer won't cease like they always have. (Parking brake is off.) Thoughts? Thanks!

 

[Scar59]

Hello. A minor, but noisy, new issue just popped up on my M934. Even after primary and secondary air pressures build well past 60psi, the air pressure light and buzzer won't cease like they always have. (Parking brake is off.) Thoughts? Thanks!

At what pressure does the light and buzzer extinguish? Does the truck produce 120 psi in both tanks?

 

[98G]

Corroded sensors and likely moisture in the tanks.

When these fail, they fail "on".

 

[The HUlk]

Corroded sensors and likely moisture in the tanks.

When these fail, they fail "on".

Yeah, I'd start by inspecting the pressure switches to determine if cleaning or replacement is in order.

 

[juanprado]

if air pressure switches on tank good, then likely the notorious fail safe warning module/buzzer. There has been at least 3 different revisions of this jewel...

 

[simp5782]

It is sensors with gunk in them. My 934 did it today. The humidity here plays heck with em. Especially with the rain we have had. Then again I hadn't moved it in 2 months.

 

[The HUlk]

if air pressure switches on tank good, then likely the notorious fail safe warning module/buzzer. There has been at least 3 different revisions of this jewel...

Yeah, jewel alright. Mine was inop when I purchased the truck. I bought a "new" one last summer and within six months when it got cold out the buzzer became intermittent. The lights function as they should. :/

 

[therooster2001]

It's the pressure switch(s) or a bad ground. The TM has a thorough testing procedure to isolate it. I have a bunch of those fail safe if you need it, all are take offs.


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[captcarc]

I'm getting lost in the wide selection of manuals. Please tell me which manual(s) are best for me. M934 Expansible A-2 I think with NHC-250. Thanks!

 

[M813rc]

There are two pressure switches, one for each set of tanks. You can test them by bypassing the switch - unplugging the wires and hooking them straight to each other. When the buzzer turns off, you've found the bad one.

On my 931, there is one up top and easy to reach, and the other which is down below and hard to get at. You can guess which one failed!

Cheers

 

[Tinstar]

I'm getting lost in the wide selection of manuals. Please tell me which manual(s) are best for me. M934 Expansible A-2 I think with NHC-250. Thanks!

No offense intended, but do you not know what your truck is powered by or exactly which model it is?

 

[juanprado]

The easiest to use and the most comprehensive including abs brakes are the newest 5 part tm 9-2320-272-23-1 -2 -3 -4 -5
You will need to look in index to see which volume has the fail safe warning module troubleshooting flow chart.

http://www.steelsoldiers.com/showthread.php?121487-TMs-for-M939-Series-Trucks

The older 4 part series tm 9-2320-272-24-1 does not have the same work package / trouble shooting flow charts nor abs brakes.

 

[captcarc]

Thanks for the tip on the manuals juanprado! To Tinstar, no offense taken. The "I think" in my message tied to the A2 configuration. I think it's an A2 because it has ABS, but does not have super singles or CTIS.

 

[MtnSnow]

With the NHC 250 motor and no CTIS and does not have Super Singles then you have what is quite often called an A0 truck.

Is the truck your asking about the one in your avatar?

Edit never-mind I found where you said it's a M934 Expansible. and that is what you have. It is NOT an A-2 as the A1's have the 250 motor & super singles, The A-2 have the 8.3 CTA turbo motor with CTIS & Supersingles. the straight truck M934 or sometimes referred to as a M934a0 truck has the NHC 250 motor & duals.

 

[MtnSnow]

Also NONE of the M939 series trucks came with ABS when first issued. ABS is a MWO (Modification Work Order) retrofit that was supposed to be done.

See attached PDF of the MWO

View attachment MWO 9-2320-272-35-1.pdf

 

[captcarc]

My avatar is the M35A3 that I used to have. My M934 Expansible has "modern" duals, NHC250, muffler, ABS, no turbo and no CTIS. In the deuce world, that would make it an A2. So, in the 5-ton world, it is an M934-A0?

 

[98G]

It's an M934.

Frequently, though incorrectly, called M934A0 for clarity.

"A" followed by a number is revision level of the original design. It has nothing to do with being reworked,revuilt, or MWOs.

It is difficult bordering on impossible to find a 939series truck without ABS. ABS has nothing to do with revision level. All 939series trucks were supposed to be retrofit with ABS....

 

[MtnSnow]

In the M934 trucks the breakout would be

M934 - NHC 250 motor with Dual rear wheels & tires - This is what you have
M934a1 - NHC 250 motor with Super Single tires
M934a2 - 8.3 6CTA turbo motor with Super Single tires & CTIS

 

[kfrosty]

Picking up on this thread as I'm starting to have flaky results with my alarm. Now it's not shutting off until 110 psi then it's kind of random when it comes on and off.

I took one off and curious as if anybody else has tried cleaning and what can be used? Air, brake cleaner, pipe brush etc?

Mine tends to happen when it sits. But I just drained the tanks as well as took the sensors out. There doesn't appear to be any moisture.