Leaky CTIS on M35A3

[BadMastard]

That's genius motomacguyver. I wish I had thought of that before I took the wheel off and replaced everything, but I found a leaking xring, so it's paid off already. I had connected an air line to the hollow stud and pressurized it and immediately the ctis started honking, but no air leaks from the fittings. I'll need to add breather tubes, but that sounds about perfect to check with.

 

[rossbart]

Hey Ross-

Your CTIS system plumbing likely is clogged or has a leak at a plastic joint. The system isolates all the tires and vents the pressure in the lines when shut down. It initializes by blowing little puffs of air to open the wheel valves. It the measures the pressure in the line to get the tire pressure, assuming that the wheel valve opens. If the system can't build 20psi in the lines, the wheel valve doesn't open. It will repeatedly try for a number of times and if it doesn't sense any pressure when 'listening' between puffs, it says 'Flat'. The system will fail to build or hold pressure if one of the plastic tubing joints is loose or the tubing or valves gummed up with oil and snot. The system is very sensitive to dirty air lines and that's why there's a Haldex filter/dryer system added to the air system.

The best way to trouble shoot is to first make sure the air dryer is working properly. Make sure the filter and desiccant cartridges have been serviced recently. The A3s I've seen all had poor air dryer maintenance. That's a cheap fix and will also avoid issues with the air assist steering and air boosted brake system.

Next make sure things are tight at each wheel. The slip on plastic plumbing ends are notorious for having the tubing work loose. Make sure the tubing is seated in each one. Next, never use CTIS until you've driven a few miles, regardless of temperature. This is to give the axle seals a chance to seat. Otherwise you risk blowing a seal and that is a very ugly repair. This instruction is in the TMs. The steps I listed cover the most common issues. It is likely that it will enable your system to work. One last informational item: the CTIS system connects all the tires together when active. On the A3, you cannot measure or fill a single tire or axle. The system will attempt to equalize all of them and fill the combination to the pre set pressures, depending on mode and speed. It will not fill flat tires because the tire must have 20psi in order to pop the isolating wheel valve open.

Thanks Rusy Gears for the input and suggestions. I have not serviced the dryer & filters but have them in hand and was just waiting for the next free, weather tolerable day to do so. I also had the delight of finding a box of parts left in my truck courtesy of Uncle Sam containing (amoung other things) six brand new wheel valves. Thought I'd service the dryer/filters and then replace all of the wheel valves and look closely while I'm in there for oil in the hollow studs, bad connections, etc.. I'm also wondering if it would be a good or bad idea for me to blow air into the hubs to see if they hold pressure like the TM troubleshooting section outlines. It would be good diagnostics and easy to do at that point. But, is there a chance that the test will CAUSE an ottherwise acceptable seal to blow out? Your thoughts on that?

Lastly, I saw a NOS CTIS manifold for sale on ebay for $99.00. Sounded like cheap insurance so I bought it. I guess if the above measures do not fix it I could put on the new manifold...

Thanks,
Ross

 

[Rustygears]

The mechanical parts of the system are really simple. The manifold has a series of solenoid operated valves. One is a mass dump valve used to slam the wheel valves shut to isolate each wheel and vent the lines. Another is a fill valve used to pass line in air at 120psi to the manifold. The last is a slow vent used to bleed down the tires to reduce inflation pressure. It works just like the valve used to operate your sprinklers. There are two electrical pressure sensors. One senses the manifold pressure, which is also the tire pressure when the wheel valves are open. The other measures the line in air pressure to sense if the system pressure drops below 70psi and then cause the control head in the cab to inhibit operation. The manifold has very few parts and the failure is usually due to being gummed up with snot and oil. It is easily disassembled and cleaned up.

The wheel valves inhibit airflow until there is a positive pressure on both sides in excess of about 20psi. This is why the system won't fill a flat - the valve can't open. If the valve is open and the flow exceeds a certain rate, the valve slams shut. This is how the system closes the valve and isolates each wheel - it just rapidly vents the line by rapidly dumping the pressure from the system via the manifold using the dump solenoid. To deflate, the system is pressurized to open the wheel valves and the air is bled slowly in bursts using the slow bleed selenoid. It is bled slowly enough to avoid closing the wheel valves. In between bursts, the manifold pressure sensor sends the measured manifold/tire pressure to the control head to decide if another bleed-down burst is necessary to achieve the predetermined setpoint. Filling follows basically the same process as deflation, except the fill valve is pulsed instead of the bleed valve.

The plumbing to the wheels of each axle are connected in parallel via a tee connector located above each differential. A larger plastic tube runs from each of the 3 axles to the manifold assembly. Inside the manifold, all 3 axles are tied together. Once the wheel valves open, all 6 tires will try to equalize to a common pressure and the system will in principle measure the common pressure and manage it. It is not possible on the A3 system to measure or manage individual wheels.

 

[rossbart]

Thanks Rusy Gears for the input and suggestions. I have not serviced the dryer & filters but have them in hand and was just waiting for the next free, weather tolerable day to do so. I also had the delight of finding a box of parts left in my truck courtesy of Uncle Sam containing (amoung other things) six brand new wheel valves. Thought I'd service the dryer/filters and then replace all of the wheel valves and look closely while I'm in there for oil in the hollow studs, bad connections, etc.. I'm also wondering if it would be a good or bad idea for me to blow air into the hubs to see if they hold pressure like the TM troubleshooting section outlines. It would be good diagnostics and easy to do at that point. But, is there a chance that the test will CAUSE an ottherwise acceptable seal to blow out? Your thoughts on that?

Lastly, I saw a NOS CTIS manifold for sale on ebay for $99.00. Sounded like cheap insurance so I bought it. I guess if the above measures do not fix it I could put on the new manifold...

Thanks,
Ross

Spent the afternoon servicing the air dryer assembly. Took it off the truck so I could inspect, clean and service it well. Replaced the two filters on top. There was a bit of moisture and gunk in the coalescing filter cavity but the coalesent filter itself wasn't really that dirty. Replaced it and the desiccant spin on filter and o-rings as well as the dryer purge valve. Tested it and everything was good. Took it for a spin to town (about 10 miles total) and turned on the CTIS half way into trip. Tires were low due to me having it on Mud/Snow setting last (though oddly it had seemingly only deflated the rear four tires and the front two were still aired up pretty round). The system initially did appear to be airing up the tires as the tire pressure started rising from 12 psi area. But, it could only manage to show a max of 17 psi tire pressure on the console when set to Highway mode after several miles at >2,200 rpms? Manifold pressure test was no better and actually couldn't even get past about 10 psi when it cycled this time - then went to Flat? mode.

Again, front tires never seemed to deflate much so were still aired up (and equally) though the two back axles seemed to have pretty equal (and low) tire pressure. What would make the front axle respond differently than the rear two? Is that a manifold issue, clogged front tubing, bad rear seals in BOTH rear axles???

So, just aired the tires up when in town at the truck stop and turned the system back off. When under the truck I did note that the discharge port on the manifold was quite oily and cruddy looking. Is that indicative of a seal failure or manifold problem. Like I mentioned, I have a new manifold in transit and (though I intend to and will asap) have not taken off the CTIS wheel guards yet to check wheel valves, tubing, hub pressure, etc.. There may be some leaks but nothing so loud that I can hear it over the truck when it's running...

Do these symptoms turn any light bulbs on in anyones knowledgeable heads?

Thanks,
Ross

 

[blueeagle79]

Hello Rossbart, my m35a3 has the same symptoms as yours. I can hear a leak in the brake backing plate on the rear axle. Did you solve your problem? Thanks!!!

 

[tomcata3]

Hi Guys
ctis can fill a flat tire, you just hit button twice and hold it, the system goes into run flat mode
I did this on my truck

 

[1 Patriot-of-many]

Hi Guys
ctis can fill a flat tire, you just hit button twice and hold it, the system goes into run flat mode
I did this on my truck

Could you expand on that? Hold which button and for how long?

 

[tomcata3]

I picked up a truck a meade it had 3 flats, ctis said flat on screen, first thing I did was pull out throttle to about 1500 rpm then hit highway button once, then hit second time and held it in till screen says something like run flat mode activated, while this was running I noticed some valve stems had been loosened, after it filled tires I turned of system off to reset it back to normal mode

 

[chvss65]

correct

I picked up a truck a meade it had 3 flats, ctis said flat on screen, first thing I did was pull out throttle to about 1500 rpm then hit highway button once, then hit second time and held it in till screen says something like run flat mode activated, while this was running I noticed some valve stems had been loosened, after it filled tires I turned of system off to reset it back to normal mode

that is in the TM,, short sentance and easy to overlook, I was just going to add your post on run flat mode

 

[TLambert]

Cannot manually inflate

Been a while since you all have commented, however worth a shot. I had activated the CTIS as the most rear passenger tire had been losing air during trip. I put on the system and indicated FLAT for a period of time but then inflated. I made it thru my trip and and got out of vehicle. Upon return, 5 minute, and left vehicle running to cool down t/c, the most rear driver side was completely flat. During this time, the CTIS was inadvertently left on. Previously, the passenger tire was "low". However, the passenger side held pressure and has done do for past two days. When I used emergency connector, the schrader valve will not allow air into tire and I can hear it back feeding the manifold. I tried to manually inflate with the CTIS in the off position. Any ideas? Bad wheel valve?

 

[wb9btz]

From your description it sounds like a stuck CTIS wheel check valve. The only way air from the schrader valve would backfeed toward the CTIS manifold is if the check valve is stuck open. With the CTIS turned off or with a major leak in the CTIS feed lines, the check valve is supposed to "slam" shut to keep the tire from going flat. Try disconnecting the hose from the hollow wheel stud, plug it, and then see if your tire will air up and hold air. If it still will not hold air, you may also have a bad grommet where the valve stem goes through the rim. From what I have read, the CTIS check valve is pretty easy to disassemble, clean with mineral spirits, and reassemble. This usually results in normal operation, assuming proper reassembly and no damaged gaskets. If you find oil in the hollow wheel stud and/or CTIS check valve, you probably have a leaky outer seal in the spindle and will need to clean/repack the wheel bearings and replace the seal, including the cork that goes in the keyway. Differential oil getting into the CTIS check valve can gum it up and make it stick. Good luck.

 

[nmwildman013]

We had a similar problem and found the epoxied part broken and coming apart on one rear axle. Tires would randomly air up and down or go flat. Fix for us was to remove all that garbage, converted the axles back to A2 bearings and capped the tire valves off. Worked fine and still working fine a year later. I did leave the front hooked up and CTIS still operates on the front (in case of deflation). The A3 CTIS axle installation was the most half baked conversion I have ever seen. Obviously a temporary solution, overly expensive (bearings) and not intended to be repaired easily.

 

[armyrino]

Does anyone have a complete wiring diagram for the CTIS in an M35A3. I just picked up a M35A3 and the wires are all disconnected at he battery. Just want to make sure. I could trace them all down and meter them out but it would be much easier to have the wiring diagram. Thanks in advance for your help.