M923A1 Abs Light

[fsearls92]

I just bought a M923A1 and the ABS light is on. What can the problem be? Where do I start?

 

[firefirefire90]

Check your ABS sensors for one. They might have some grime in them messing something up. Other than that, I'm sure a more experienced member will chime in shortly

 

[seano11]

Most of the time they are broken off or just loose at the hubs I know sometimes if the truck has crossed thru deep water the abs light will come on truthfully ABS is just a pain in the rear end

 

[fsearls92]

Do I need to remove the tires to check the ABS sensors? Is it a big deal that the light is on?

 

[seano11]

All depends how well its hiden. Just look behind your tire and see if you can see a wire going to the hub. It not working isn't really a huge issue on a truck like this just have to be a little more careful with your breaking

 

[fsearls92]

Thanks, I will check it out to see what I find. I was hoping it wasn't important; and the truck stops great!

 

[rrrr]

Keep us updated on what you find. Since this trucks are coming out in mass we need to get a good database down in the forum for fixing such issues. My 932A1 has had a few unique issues that took a few days to trouble shoot.

The TM's for the 9 series trucks are not the best. I had a forum member help me on the phone to finally fix my air
brake issue !

 

[jtron79]

There is a sticky in the 5 ton listing from Chris about the differences in your truck with and without abs, I personally wouldn't run the truck without it, the problem being it stops too well, causes fishtailing on pavement and is the cause of many deaths.

 

[emmado22]

https://aeps2.ria.army.mil/serviced.cfm

This should help.



12 DEC 05

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SAFETY OF USE MESSAGE
TACOM #06-007

MSG DTG: (Zulu): 2005/12/12 18:06:11Z
CLASSIFICATION: UNCLASSIFIED (750-1B)
FROM: TACOM SAFETY OFFICE- TACOMSAFETYOFUSE@tacom.army.mil
SUBJECT: Safety Of Use Message (SOUM), TACOM Control No. SOUM 06-007, "Operational" Safety Of Use Message. Anti-lock Brake System (ABS) Warning Sticker, NSN 7690-01-530-5506, M939 Series Vehicles. Model Number, NSN, LIN and Density as follows:
Trucks, Cargo, Dropsides, wo/winch M923 (2320-01-050-2084), M923A1 (2320-01-06-4087), M923A2 (2320-01-230-0307), LIN: X40794, Density: 14,879
Trucks, Cargo, Dropsides, w/winch M925 (2320-01-047-8769), M925A1 (2320-01-206-408, M925A2 (2320-01-230-030, LIN: X40931, Density: 3,986
Trucks, Cargo, Extra-Long Wheel Base, wo/winch M927 (2320-01-047- 8771), M927A1 (2320-01-206-4089), M927A2 (2320-01-230-0309), LIN: X41105, Density: 867
Trucks, Cargo, Extra-Long Wheel Base, w/winch M928 (2320-01-047- 8770), M928A1 (2320-01-206-4090), M928A2 (2320-01-230-0310), LIN: X43845, Density: 434
Trucks, Dump, w/o winch, M929 (2320-01-047-8756), M929A1 (2320-01- 206-4079), M929A2 (2320-01-230-0305), LIN: X43708, Density: 2,363
Trucks, Dump, w/winch, M930 (2320-01-047-8755), M930A2 (2320-01-230- 0306), LIN: X43845, Density: 141
Trucks, Tractor, w/o winch, M931 (2320-01-047-8753), M931A1 (2320- 01-206-4077), M931A2 (2320-01-230-0302), LIN: X59326, Density: 6,995
Trucks, Tractor, w/winch, M932 (2320-01-047-8752), M932A1 (2320-01- 205-2684), M932A2 (2320-01-230-0303), LIN: X59463, Density:1,047
Trucks, Van, Expandable, M934 (2320-01-047-8750), M934A1 (2320-01- 205-2682), M934A2 (2320-01-230-0300), LIN: X62237, Density: 1,535
Trucks, Medium wrecker, M936 (2320-01-47-8754), M936A1 (2320-01-206- 407, M936A2 (2320-01-230-0304), LIN: X63299, Density: 1,862
Truck, Chassis, M942 (2320-01-047-8745), M942A1 (2320-01-205-2666), M942A2 (2320-01230-0287), LIN: KC0010, Density: UNK
Truck, Chassis, M944A1 (2320-01-205-2667), M944A2 (2320-01-230- 028, LIN: KC0080, Density: 4
Truck, Chassis, M945 (2320-01-050-4894), M945A1 (2320-01-205-266, M945A2 (2320-01-230-3261), LIN: (BRIDGER) X48216, Density: UNK.
TO VIEW ORIGINAL MESSAGE: CLICK HERE

​

​

​

MENU

DISTRIBUTION
PROBLEM
USER ACTIONS
TACOM/PM ACTIONS
SUPPLY STATUS
POINTS OF CONTACT
LAR INFORMATION

​

1. DISTRIBUTION: {Menu}
A. MACOM Commanders will retransmit this message to all subordinate Commands/Activities within 24 hours of receipt of this message and acknowledge receipt of this message within five working days to: CDRTACOM, Warren MI, AMSTA-LC-LPIM, DSN 786-6096, Commercial (586) 574-6096 or DDN address: safetyofuse@tacom.army.mil.
B. MACOM Commanders will also track and report compliance of this message for all subordinate Commands/Activities to: Mr. Terry Callahan, M939 Quality representative, AMSRD-TAR-E/TACT (586) 574-8450 or DSN 786-8450 email terry.callahan1@us.army.mil NLT 30 days from receipt of this message.
2. PROBLEM : {Menu}
A. Reports from operators of M939 series vehicles equipped with anti-lock brakes (ABS) have stated that they are not sure of the meaning of an illuminated ABS amber light on the dash panel. Some operators believe that when the light comes on the system is operating properly, while others admit that they are not quite sure what it means. Drivers must be made aware that a steady illuminated ABS dash light indicates the vehicles anti-lock braking system is malfunctioning. Currently, the ABS dash light is marked only with a tag labeled "ABS" and gives no further explanation of the meaning of an illuminated lamp.
B. Normally, upon start, the ABS light will illuminate for three (3) seconds and then go out. This is a normal ABS self test. These procedures are described in the PMCS section of TM 9-2320-272-10 Pg. 2- 44. If the amber light comes on and stays on, a malfunction exists, the maximum speed limit is reduced to 40 MPH. (Table 1-9A Operators Manual) Different braking techniques are required driving without ABS. See paragraph 3B and 3C below.
3. USER ACTIONS: {Menu}
A. Driving with ABS functioning: (ABS light off) A fully functional ABS system allows the wheels to intermittently roll while drivers use full brake pressure. This rolling action allows the driver to regain traction control and stability on the rear wheels.
B. Driving with ABS malfunctioning: (ABS light on) Drivers need to be aware that air brakes are very sensitive when trucks are lightly loaded, empty or when driving on wet/slippery pavement. This is especially evident when the ABS light is illuminated. The brakes must be applied gradually to avoid locking up the wheels. Although a steadily illuminated ABS amber light does not deadline the vehicle, it does render it Not Fully Mission Capable(NFMC). The M939's must revert back to the 40 MPH maximum speed limit imposed by Safety of Use Message 98-07.
C. Complete driving instructions for M939's series vehicle with or without ABS, are found in the operators manual TM 9-2320-272- 10 C-2. (Starts on Pg. 2-156.2)
D. Maintenance personnel must prioritize restoring any vehicle's malfunctioning ABS system. The Haldex Diagnostic Info Center is available using NSN 5895-01-515-9443 and should be used to record malfunction fault codes to make accurate maintenance diagnoses. The ABS fault codes are stored in ABS Electronic Control Unit (ECU) and can be retrieved using the Haldex Diagnostic Infocentre. This diagnostic tester plugs in under the passenger side of the cab. Troubleshooting should be accomplished as soon as mission and time allow.
E. Although the current TM 9-2320-272-24 does not carry ABS Technical information, more detailed information has been available in TB 43-001- 62-01-1 (April 2001). This Technical Bulletin, troubleshooting, and diagnostic information for the Haldex Infocentre ABS diagnostic box, can all be found by using the following web sites:
https://aeps2.ria.army.mil/commodity/pubs/tacom/bulletin/m939_fov.pdf
https://aeps2.ria.army.mil/commodity/pubs/tacom/bulletin/m939_infocenter.pdf.
F. If problems are encountered at the above links, go to AEPS homepage: https://aeps.ria.army.mil. Use the "Site Search" box at the top and type the word "M939". Press "Enter" and go to articles "M939 FOV Antilock Brake System Tire and Wheel Assembly", also "M939 Infocentre Instruction for Handheld Diagnostic Tool".
G. There is a new ABS warning sticker (NSN 7690-01-530-5506) which clearly informs the operator of the meaning of the ABS warning light. Application of this sticker is mandatory, but the equipment still remains fully mission capable (FMC) without it being applied. Units shall order and install individual stickers for their entire density of M939 variants equipped with ABS. In the event stickers are unavailable when requisitioned, they will be backordered and shipped as they become available.
H. The new ABS sticker verbiage states:
1. Steady illuminated lamp indicates a malfunctioning anti-lock brake system.
2. If malfunctioning, use gradual braking techniques listed in TM 9-2320-272-10 (Operation W/O ABS).
3. 40 MPH maximum speed with steady lamp.
I. ABS warning stickers will be placed on the ledge directly below and centered on the existing ABS malfunction light.

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Ensure dashboard surface area is clean, dry and non-greasy before applying sticker. ​

4. TACOM/PM ACTIONS: {Menu}
TM 9-2320-272-10 manuals will require future updates for operator instructions. Updates are forecasted for first quarter 2006.
5. SUPPLY STATUS: {Menu}
32,000 ABS warning stickers, NSN 7690-01-530-5506 have been produced and are available in the supply system.



Commodity Services
Maintenance Services
Safety 1st

 

[Krink545]

Mine has the same problem.
Ill post what I find.

 

[flashgordon]

The ABS light has been on in my truck since the day we met. About 1000 miles later it's still on and I dont worry about it. I dont believe any vehicle can stop "too well." I drive big trucks with and without abs all the time so, your mileage may vary. I have been going 60 MPH down my dirt road and locked em up to see what she was capable of and nothing out of the ordinary in my opinion. I dont mind all four rears locking up. At least the brakes work, thats better than the alternative. Just ease off the pedal, wheels start turning and she never got out of control. Like it has been said here before " some 20 year old private not paying attention going to fast will have problems without ABS"
-FLASH-

 

[nf6x]

I just bought a new Haldex diagnostic unit on eBay. At this particular instant, the seller has another new one like the one I bought, and a few used ones in various conditions. I don't know how common these boxes are, but maybe now's the time for M939-series ABS-equipped truck owners to grab them up?

The links above to the manual didn't work for me because they appear to be on a secured site that requires a valid certificate for access. I Googled up the instruction manual here, though:

http://www.haldex.com/en/North-Amer...nfocenter_Instruction_Manual_L31204_11-03.pdf

My M923's ABS light doesn't indicate any faults, but I decided to get the diagnostic box out of curiosity and a desire to be prepared if and when I have any ABS problems in the future.

 

[lost in the bush]

ABS Light and Sticky throttle

HI

One of our new 923 has the ABS light on as well. A bigger concern is when we come to a stop and put in "N" to close down the truck. The engine races up to high RPMs until I reach down and pull up Go pedal?

From my reading I think the ABS was added because of a similar issue?

 

[nf6x]

If you have to pull up the accelerator pedal, then that sounds like either a missing/broken accelerator return spring or a sticking accelerator pedal/linkage. It would be a separate problem from the ABS warning light. Both problems are things that you need to fix before putting the truck on the road again! The ABS was added to keep drivers from locking up the wheels when braking hard with a light load, and has nothing to do with a sticking accelerator.

It shouldn't be too hard to figure out the accelerator pedal problem. Make sure that the return spring is present, not broken, and not rusty. See if the linkage or pedal is sticking at all. If it is, you may need to start disconnecting parts of the linkage to narrow down which part is sticking. My truck came with a similar problem, and it turned out to be a rusty pivot at the bottom of the accelerator pedal. I temporarily freed it up by disconnecting the linkage, lubricating the hinge, and working the pedal back and forth. I got a new replacement pedal from eBay that I'll install soon.

Now, only racing when the truck is put into neutral sounds odd, so maybe there's something else going on that I don't know about yet. There's a mechanical linkage from the accelerator to the transmission if I remember correctly, so maybe something funny is going on in the transmission? If you don't find a problem with the accelerator pedal, return spring, or its linkage to the injection pump, then maybe you need to start looking at the transmission?

For the ABS light problem, I haven't had to fix that before. The first thing that I'd do would be to plug in the Haldex ABS diagnostic box that I got off eBay. There's an ABS diagnostic port under the right side of the dash, next to the larger STE/ICE-R diagnostic port. I don't see any of them on eBay right now, but maybe another M939 series collector near you has one?

 

[lost in the bush]

Thank you for your helpful response .

 

[rrrr]

Well, my ABS light just started coming on. It comes on after I start driving the truck. I took a look at the system and the control unit is between the two rear axles. Sensors on my truck are only on the last axle ! So, only the rear most tires are monitored. Since I get a good self test on start up I will pull the two rear wheels and drums and check the exciter ring for debris and verify that the sensor itself is clear. I will take a picture and post results later.

 

[juanprado]

All 4 rear drums are supposed to have sensors through the backing plate and exciter rings on the drums. There are 2 sets of valves with solenoids. The first valve with a solenoid/ electronics closest to the dryer does the middle axle, The back axle valve inbetween the axles has the solenoid/ electronics for the back axle plus it has the abs module with a 24 pin (?) connector.

Only real way to asses the situation is to hook up the info centre, get the codes, and proceed accordingly.

There has been other posts about the 2 fuses and the finicke power supply coming off the pcb box and the proper shut down sequence.

I have attached the abs schematic that is also available in the download section.

I also have supplied the info centre manual that I got from a fellow ss m939er

All these parts are midland/haldex and available commercially / NAPA as well as some surplus dealers. Hold on to something rigid and brace yourself for some of the prices.

Best of Luck!

 

[rrrr]

Since the unit self tests fine and only indicates a problem after I start moving i'll start at the transducer and exciter first. I will take a close look to see if the middle axle has anything but a quick look appears that only my rear most axle is abs monitored. I have the manual and read through it but its not really helpfull.


I just went through the manual again. Both rear axles are abs protected but the sensors are only on the rear axle !

 

[Lonekazoo]

Same boat here: Solid ABS light, '85 M923A1--on since recovery. I've checked both fuses--the 15A was blown and immediately blows when replaced, 3A is OK.

I've gone through the TM, ABS maintenance sustainment handout, etc, and can't identify a troubleshooting path for the fuses, though it looks to me like it's probably in the Control box at this point. Any suggestions short of using the diagnostic tool? I'm trying to obtain one since I have friends with M939's, but it looks like it might take a while.

I'm getting tired of keeping it under 40mph

Thanks!

 

[rrrr]

Try pulling the electrical connector on the abs unit between the rear axles. Make sure its clean and not grounding out. Then put in silicone, aka di-electric grease, and put back together and replace the fuse and see what happens. It sounds like you might have a grounding short somewhere.

These trucks operated a long time without abs. I won't slow down without it however I will give myself more room and be more cautious.