M923A2 CTIS Problem

Jbulach

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I finally got some time during my furlough this week to look into my 5 flashing light problem. Once the truck hits 120psi, the system does a check and goes right into the 5 lights. I checked the tires and the front was at 50, the middle was at 50 but the rear was at 40, both sides. I aired the back up to 50 and tried again with the same result. I checked the axle vents and they are not leaking. The two back tires both had very small leaks at the bottom of the wheel valve where the hose goes into it. I took the wheel valve off, cleaned everything up, put some thread tape on and re-assembled it. The leak is fixed. however, I noticed there was a little oil in one of the wheel valves. I'm guessing that shouldn't be there?

The CTIS worked perfectly since I got the truck up until January.

I also found on one of my tanks, the shutoff valve was leaking a good air. I haven't looked yet but I'm assuming those aren't re-buildable?
You may have a bad hub seal allowing a little gear oil into the CTIS. That could likely swell the diaphragm in the wheel valve as well as the QR valve flap and cause problems.

I should have some used wheel valves around, maybe even a new one or two. Let me know if you need them to try.

I think most people just go to full port ball valves when the tank shutoffs go bad.
 

Jbulach

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Don't know if this will help but it is there.
IIRC you do not need to dump the tires down to emergency pressure when using the run-flat button. You can hit run-flat and Hwy just the same, and it should keep the CTIS from timing out as quickly.

Stellaevil is the subject matter expert on this and could correct me if I’m wrong.
 

BigDumbMike

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I have an m923a2 where the previously working fine CTIS has stopped responding after having some electrical work done on the truck (fixing up the wiring behind the dash panel to fix the ignition and energization switches that start the truck), but I am not getting the "5 lights" problem. Tires neither inflate nor deflate (they are inflated right now but front tires are more inflated than back ones).

The 5 button letters (like HWY, SAND) are lit (when I am not in run-dark), but there are no red circular lights on (either solid or flashing) and pressing the various buttons. Reading the TMs indicates that my problem may be faulty PCU wiring or solenoids.

Oddly, the low pressure/e-brake alarm also stopped working at the same time. Replaced the buzzer which didn't seem to be the problem. The 2 "alarm lights" behind the steering wheel (that are red to indicate low pressure and e-brake) also aren't lighting now... even though the truck gets to 120PSI and is otherwise operational. I understand this could be totally separate from the CTIS but seems odd they would get wonky at the exact same time.

Edit: I neglected to mention that during the electrical at one point when the truck was turned on a pressure gauge caught fire (behind the glass) temporarily. I saw another post on this site indicating this may have been a result of the voltage regulator failing. Electrician thinks its because the wire harness got pulled too tight when I was trying to start the truck (energizer switch could rotate indefinitely rather than just up/down toggle to electrify the truck).

Any/all tips appreciated... thanks gents
 
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Stellaevil

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You may have a bad hub seal allowing a little gear oil into the CTIS. That could likely swell the diaphragm in the wheel valve as well as the QR valve flap and cause problems.

I should have some used wheel valves around, maybe even a new one or two. Let me know if you need them to try.

I think most people just go to full port ball valves when the tank shutoffs go bad.
FYI, if you are new to these CTIS threads; I still work for the company who designed and manufactures these systems, 30 years now. 939, LMTV, MTVR, and JLTV. Happy to help those who serve.

Air seal leaks; while the system is inflating, check the axle vent tubes for pressure build up. 5 lights following the first pressure check is the tire reading at the PCU < 5.0 psi. Because the tire pressure fills the air lines from the wheel valve through the hubs and up to the QRVs, the large leak has to be between the PCU and the top of one of the QRVs. The only other leak could be a QRV not sealing during the pressure check. Have someone in the cab turn on the truck and feel for air passing out the QRV vent during the check or during an inflation. To eliminate the PCU as the problem, remove the are line going to the axles and plug the PCU port. The first pressure check will read high and the system should go solid "highway" Press CC and the system should try and deflate.

Hope this helps, good luck.
 

Stellaevil

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You may have a bad hub seal allowing a little gear oil into the CTIS. That could likely swell the diaphragm in the wheel valve as well as the QR valve flap and cause problems.

I should have some used wheel valves around, maybe even a new one or two. Let me know if you need them to try.

I think most people just go to full port ball valves when the tank shutoffs go bad.
The CTIS will only fault out on the pressure check if the pulse of air drops to below 5.0 psi. That is a pretty big leak. Hard to hear with the engine running so hook up shop air and run the system. If you don't have enough pressure >120 psi to close the switch, disconnect and short the harness side and the system will kick on. You should be able to hear the leak now.
 

70deuce

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Franktown, CO
My problem is that after driving my 936A2 on a 50 mile trip, system working perfectly, after starting the truck to come home the system started to dump pressure on all 6 tires, no flashing lights on the controller or any other indication of a malfunction. I don’t know how low they were going to go because I disconnected the controller. Swapped controllers with same results. Controller is disconnected and all the tires maintain 80 PSI so that’s where I am now. If the controller is plugged back in it starts to dump pressure almost immediately. Any thoughts?
 

Andyrv6av8r

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My problem is that after driving my 936A2 on a 50 mile trip, system working perfectly, after starting the truck to come home the system started to dump pressure on all 6 tires, no flashing lights on the controller or any other indication of a malfunction. I don’t know how low they were going to go because I disconnected the controller. Swapped controllers with same results. Controller is disconnected and all the tires maintain 80 PSI so that’s where I am now. If the controller is plugged back in it starts to dump pressure almost immediately. Any thoughts?
My problem is that after driving my 936A2 on a 50 mile trip, system working perfectly, after starting the truck to come home the system started to dump pressure on all 6 tires, no flashing lights on the controller or any other indication of a malfunction. I don’t know how low they were going to go because I disconnected the controller. Swapped controllers with same results. Controller is disconnected and all the tires maintain 80 PSI so that’s where I am now. If the controller is plugged back in it starts to dump pressure almost immediately. Any thoughts?
That's normal in my experience. Tires heat up on the road, pressure increases and it deflates to normal pressure upon startup. Give it a minute to situate itself.
 

Jericho

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How did you bypass the pressure switch? My truck is a NOS M932A2 complete 2011 rebuild with 6 hours and 13 miles on it. Everything on the truck is new. It worked fine on recovery, pulled a M146 trailer home with it 300 miles. Have used it for several months off roading and hiway use using the CTIS flawlessly. Suddenly had same issue as above, front tires deflated with five flashing lights. Read the 2012 operation TM. Drained system, fired it up and hit "run flat". System could be heard running air checks and then five flashing lights again. I ended airing up all the tires to 80psi using the outside valve stems. Fired it up, same five flashing lights and the tires aired down automatically to 53psi on all tires. Read more on TM, turned truck off including master battery switch and disconnected CTIS cable from plug on transmission tower. Let sit for a few minutes, plugged it back in. Long story short, seemed things were cycling correcting for a couple minutes and then again got five flashing lights. Any suggestions? I also just found and printed 122 pages of CTIS "Troubleshooting Procedures" from the 2012 updated TM's. I'll be going thru those diagnostics. Seems that we all are having a similar issue with the front tires airing down and getting five flashing lights.
If you think the computer is malfunctioning a hard reset is in order, the easy way to do it is simply disconnect the QD cannon plug on the back of the controller make sure power is off prior to pulling the plug , if that has no effect then you have a deeper problem
 

1 Patriot-of-many

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My problem is that after driving my 936A2 on a 50 mile trip, system working perfectly, after starting the truck to come home the system started to dump pressure on all 6 tires, no flashing lights on the controller or any other indication of a malfunction. I don’t know how low they were going to go because I disconnected the controller. Swapped controllers with same results. Controller is disconnected and all the tires maintain 80 PSI so that’s where I am now. If the controller is plugged back in it starts to dump pressure almost immediately. Any thoughts?
That sounds like a faulty pressure transducer on the pnuematic control unit. Reading high pressure so it dumps air. My guess.
 

Stellaevil

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That sounds like a faulty pressure transducer on the pnuematic control unit. Reading high pressure so it dumps air. My guess.
Sorry I don't check the site as often as I should. One scenario I can think of is that the tires were at the highway pressure and then went up due to the heat in the tires. When the system did a pressure check you may not have noticed the highway light flashing for a couple seconds. When the pressures are high the system will not deflate the pressure off and it will be still be happy. The pressures may have been too high for the wheel valves to physically close and so they would dump until the got low enough to shut. You can check the tires with a gauge before you leave and then after you have traveled for a while to see how high they get up to.
 

Andyrv6av8r

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Sorry I don't check the site as often as I should. One scenario I can think of is that the tires were at the highway pressure and then went up due to the heat in the tires. When the system did a pressure check you may not have noticed the highway light flashing for a couple seconds. When the pressures are high the system will not deflate the pressure off and it will be still be happy. The pressures may have been too high for the wheel valves to physically close and so they would dump until the got low enough to shut. You can check the tires with a gauge before you leave and then after you have traveled for a while to see how high they get up to.
That's exactly what I suggested in post #228.
 
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