LMTV CTIS does not deflate

[Konichiwa512]

Recent LMTV purchase. 5 solid lights on CTIS controller. Replaced controller with new one, now I get 3 solid lights. I followed the TM troubleshooting for 2 solid lights, since that is the closest thing to my problem that is addressed by the TM. Leak checks all OK. All four wheel valves failed to vent during the 'wheel valve vent test' on pg 2-1775 of the repair manual. I thought the valves might be seized up from many miles with the broken controller. I figured I could disassemble the wheel valves, clean out the gunk and make everything all better, but the first wheel valve I took apart looks factory new inside. The spring is greased and shiny and the air filter is pure white. Air is definitely going into the tires because CTIS keeps highway pressure in all tires when running. HWY mode on the controller flashes during warm-up, but X-C and SAND stay solid, so I figure something is not allowing deflation of the tires. Proper CTIS operation is an essential part of crushing the self-esteem of the Jeep owners at the 4X4 club, so I have to get it working. However I am out of ideas.

 

[Suprman]

It's a mechanical system that works the same as the M939A2 trucks' ctis system. Once there is around 120psi in the air tanks the system will do its initial pressure check. The system will send air to fill, or send low pressure around 12psi to hold the wheel valves open to allow air to dump. There is a solenoid valve body behind the passengers foot kick panel. If you are sure air fills into the tires. Which you can confirm by draining out some air and seeing if it refills. I would check and see if the low pressure valve or solenoid that controls it has an issue. Or swap the whole valve unit.

 

[bikeman]

You can hear the valves when they go. I'd recommend the same as Suprman. Deflate the tires manually and kick the engine on, and see what happens. a BFH may be required to assist the valves.

 

[Retiredwarhorses]

My left front ctis valve on the tire makes a shrill noise after turning the truck off, even after the tanks are purged.
if I tap on it, it stops....is that what you are referring too?

 

[Suprman]

You might have some dirt in the valve or for some reason it isn't sealing as well as it should? Does the tire leak down over time? If the system can fill air but not drop pressure the issue is more than likely the valve body it has 3 separate solenoid valves set to send different air pressure for different functions. Remember it's all mechanical past the controller with the 3 solenoids in the valve body and a pressure transducer.

 

[Konichiwa512]

Thanks for the help. I reassembled the wheel valve and tried the hammer on the others, but still no pressure release when i loosen the test screws on the wheel valves. CTIS inflated the flat tire. I read somewhere that CITS does not inflate a completely flat tire but maybe that is on other trucks. I realized this morning that Suprman must be right--the wheel valves are not getting any low pressure air to effect a deflation. I will have to check out the manifold valve assembly to see why the low pressure is not being sent. i think faulty pressure sensors should cause flashing lights on the controller, which I do not have. i also visually checked the plug connections all over first thing and they looked OK. Maybe the Army mechanics disabled the low side somehow to save themselves the headache I am getting. That would be hard to spot, since I don't know what to look for, and the repair manual does not cover sabotage.

 

[Suprman]

The solenoid that opens the valve that sends the regulated low pressure air is probably stuck or not actuating. It's unlikely that someone sabotaged the system. The valve body is a common failure item.

 

[Konichiwa512]

I guess I will squander my next weekend working on that part. Thanks.

 

[Andyrv6av8r]

I had an issue with my CTIS once on my 923A2 and I thought I had a leak somewhere. Luckily it turned out to be something totally different. I wanted to test the air lines, dump valves and wheel valves so I hooked up a shutoff valve, regulator and gauge to the air line from the PCU to the dump valves. In other words, disconnect the discharge line from your PCU and manually ( with shop air ) apply around 12 - 15 psi of air and see if your tires deflate. You can actually deflate and inflate the tires manually by varying the pressure with the regulator just like the controller does. If so, all is good and the problem is in your PCU.

 

[Konichiwa512]

Based upon what you guys have told me I am convinced the PCU, or "manifold valve assembly" as it is labeled in the LMTV repair book, is the culprit. I found a simple test for the solenoid on page 2-918.4 of the repair book. Since a fully functioning LMTV contributes to my overall health, I am going to take a sick day tomorrow and work on it. I have not seen any of these things for sale anywhere, so if it is broke, I hope I can fix it with the BFH or a WD40 infusion.

 

[Suprman]

I may have one. Don't spray wd40 into it. It likes clean dry air. No hammers either its sensitive. Why don't you make sure all the connections are good. Maybe carefully take it apart make sure there no dust or something in there clogging it up.

 

[Konichiwa512]

OK I'll take the gentle route. The TM has a test for each of the wires going into the unit, although they all appear well-maintained. I just read that this manifold also has the engine fan control in it too. How many solenoids are in this thing? The TM just has troubleshooting and replacement instructions. There is no diagram of what is inside.

 

[Suprman]

No it's just ctis that I know of. 3 separate solenoid actuated valves control air flow in the system. It's very possible you have a bad solenoid and one valve is not opening on command. The system should know something is wrong the pressure sender would give a reading and expect a certain pressure. Parts are available.

 

[Konichiwa512]

I found the electrical fault guide in the TM for "CTIS does not deflate" (table 2-7, fault no. e84) which had really easy steps to check the solenoid and the continuity in the CTIS control wiring. The solenoid was OK. Two of the three wires going to the lower plastic plug on the manifold valve assembly are bad, but they check out OK across the plugs at each end. I cut away the wire covering up until it disappears into the heater area and did not find the break. My local LMTV dealership does not have any CTIS wire harnesses, so I guess I will be doing surgery on the one I have until I find the breaks. The truck would be an 8-ton paperweight if it were not for you guys. The free Technical Manuals are a big help, but not as much as getting advice from someone who has been there. Thanks a bunch.

 

[Webrep]

Just got our m1780 and it all works perfect except the CTIS. It has all red lights on all of the time. What is my first steps to check? I did check pressure on the tires and they are all at 60 psi.

 

[Suprman]

All red lights without flashing from initial truck power on is a hardware fault. Bad controller, bad valve body or bad wiring harness. I would swap the controller with a known good one see if any change in symptoms.

 

[Konichiwa512]

There is another post by a guy in Alaska who had 5 solid lights on his CTIS controller. That was the only information about it I could find on the whole internet and led me to purchase a new control box. Once I put the new one in, the CTIS came to life, hissing and honking. Now I just need to replace the control wire harness to get it to work 100%. Does anyone reading know if it is possible to R&R the CTIS cable without draining the coolant and removing the heater like the TM says to do?

 

[Suprman]

If you know which individual wires are bad you can cut and splice to repair. Lots of sharp edges in the lmtv dash it's very possible your harness is rubbed thru somewhere and is still rubbing. The heater hoses can be accessed with the cab open. Maybe you can just flat clamp them off.

 

[Konichiwa512]

That might work, but at least one of the suspect wires splits into two before the break. Continuity is OK on one side of the split, but not on the other. That's how I figured out that the connector at the CTIS controller must be OK. The break is at or downstream of the split, but either way it is in the heater compartment. I will try to splice some wiring into the cable in parallel so the good signal still goes through. If the CTIS works then, maybe I will be inspired to snake the new wires through the heater and just go with it that way. Thanks for the idea.

 

[Konichiwa512]

The new CTIS control wire harness finally arrived. I was certain I had isolated the problem with the troubleshooting guide, but the new harness did not change a thing. I still have three solid lights. I guess the manifold valve assembly is the next thing to replace, even though the solenoids seemed to check OK.
Do both the high and low pressure air leave the manifold through the same air line? I think that is how it must work, based on what you guys have explained, and the 'Eureka' moment I had while driving to work when I realized exactly how the wheel valves work. High press air to inflate the tires, and low press air through the same line to push the diaphragm in the wheel valve open which lets the tire deflate. I think the pressure sensors for the tires must be in the manifold valve assembly as well, so it sends out a puff and measures at the manifold if the tires are at the selected pressure. Is this all correct? If so then the problem has to be the manifold valve assembly. The rest of it works for sure, since HWY mode works just fine filling the tires to full pressure. Now everything that tells the manifold to send low press air has been replaced with new parts. So the manifold valve assembly must be the culprit. It is not routing low press air when it is selected for some reason. Do I have the right idea?