Trying to educate myself on the ctis

[Hawssie]

I now have 3 939A2s and none as of yet have a working CTIS system, and none have ever worked since I have owned them. All 3 now have the 5 flashing light deal. After the first two trucks didnt work I was just going to give up on them since they are wreckers and I dont need different pressure settings for that setup. But the latest one is a Tractor, and that rides so rough unloaded that it would be nice to be able to lower the pressure for when it is unloaded. I have read the TM'S and other posts and all point to a more then minor leak to cause a 5 flashing lights. Mine first flashes the single hwy light until the trucks pressure builds up to 120 then it does the trumpet sound and blow off prior to the setting of the 5 lights. This brings me to ask how the system works and checks itself in the first place. I am not really sure how the system is supposed to control itself, and if I understand this it may help me diagnose it. I thought I could skip the electronic side for now since my problem is supposed to deal with air leaks or restrictions, and just concentrate on the air side for now. From what I can see, there are two air lines going to the pneumatic control module. One is the inlet line from the truck's air source, the other one is outgoing to all 3 of the axles with each axle having its own quick release valve then from there to the individual wheel valves. Before system start up Is this outgoing line supposed be pressurized all ready or is is it vented and then pressurized after system start up? How does the system lower and raise itself with only this one line? Does it send a lower pressure signal through this line to the quick release valves and thus cause these valves to open up and back flow air out of the tires, and release it? And if it wants to raise the air pressure at the tires does it send a higher pressure signal and this opens up the valves allowing air to flow to the tires? I know if this line is un hooked it wont release the air out past the quick release valves. Can I check for a leak by removing this outgoing line at the PCU in the cab and applying shop air downstream and listen for a leak or to where the air goes? I did this and it seems to fill up all the tires without any obvious leaks. One more question about the quick release valves. There seems to be an inlet line, and outlet line and a vent outlet with rubber dirt seal. When these are signaled to release is the air supposed to come out of this vent right on the valve or is it sent out back through the inlet line coming from the PCU and then released out the exhaust stack? If its one or the other what is this vent for and if it is released here, where is the air released into the exhaust stack coming from?

 

[Hoefler]

Not sure if this helps, but...I have an M936A2 wrecker. CTIS was not working. I adjusted the compressed air pump governor to 130 PSI (was at 120). I then un plugged the CTIS cable in the cab (TM's say that this re-sets the module). I than re-plugged the cable back in, shut the truck down and drained all of the air. Re-start truck and let it build. When the pressure went over 120, the CTIS started to become active.
It pumped up all of my tires and now works.
I think the key here is the pressure.
Pete

 

[RustyM923]

Could be something simple like a Shrader valve in the CTIS linen. 5 flashers means it's active and has a fault. The computer is working. 5 solid...is not good.

 

[corvette9]

Not sure if this helps, but...I have an M936A2 wrecker. CTIS was not working. I adjusted the compressed air pump governor to 130 PSI (was at 120). I then un plugged the CTIS cable in the cab (TM's say that this re-sets the module). I than re-plugged the cable back in, shut the truck down and drained all of the air. Re-start truck and let it build. When the pressure went over 120, the CTIS started to become active.
It pumped up all of my tires and now works.
I think the key here is the pressure.
Pete

I just did the same thing to my 939A2. Turned up the pressure at the regulator then unpluged the cable. Put the cable back on and it all came alive. Air started cycling, I hit the sand button and you could hear the air coming out of the valves. Then I hit the highway button and it aired all the tires right back up. Now I have to try the same thing on my wrecker.

 

[leo4x4]

i would try to reset the system by unplugging it and plugin it back

 

[Hawssie]

Thanks, I do unplug and plug it in every time I mess with it or try to get it to work. Actually that was the first thing I did when I picked them up from GLS yard as all the trucks had flat tires at various stages of air pressure. I didn't think about the governor though, So maybe the system doesnt have enough pressure to get started? I will try that. Thanks

 

[MO MV man]

I'm a firm believer in air pressure being the CTIS's best friend.
Check for leaks. Even the slightest one can cause the system to not reach and maintain it's full potential and keep the CTIS happy.

I had flashing lights shortly after receiving the truck.
I found my pressure relief valve to be leaking (cheap and easy fix) and I found two tiny fitting leaks (snugged down fittings).

Now the system is 120PSI and the CTIS works fantastic with no faults.

 

[1 Patriot-of-many]

http://www.steelsoldiers.com/showth...cause-Wet-Tank-Builds-to-only-70-75-psi/page3 Troubleshooting guide there. I've gotten 5 flashing lights when either I had a leak in the system or a schrader valve in the system at one of the wheel turrets. You'll also get it if one of the tires has less than 10lbs of air. If less than 10lbs of air, hold down the run flat button for a couple seconds. If you find any shrader valves where the ctis line connects with the wheel turret, use a schrader valve removal tool like that found on the top of a bottle of green slime. I'm guessing all those wheels found with a schrader valve were once on an A1 truck and those changing them forgot to remove the valve when they hooked up the ctis line.

 

[Hawssie]

Got it working

Well I got my CTIS system working now for the first time, And I thought I would describe how I was able to track down the problem(s) just in case anyone else is having similar issues. First I put a gauge inline at where the black nylon output line comes out of, the cab mounted Pneumatic control valve. On mine the black line is outgoing, the yellow line is incoming. I did this so I could also see what was going on in the system instead of only just listening to it. So after resetting the system I watched the gauge and at system start up, it would air up the line, and would get to about 60 psi then quickly drop down and set the 5 flashing lights. So I took a pair of hose clamp pliers (the kind you can clamp on a line or hose to collapse it without damaging the line) and in this case using them to just to restrict the air going out of this line and tried again. After a few tries I was able to trick the system and get it to start filling up the tires: After airing up a while the gauge read around 70 psi, the hwy light stopped flashing and the system exhausted itself, the gauge went dead, the hwy light went solid and everything was fine. But after this without the clamp and turning the truck off and back on again, thus causing the system to re-power up, it again tried to air up but ended in just setting the 5 flashing lights again. So I knew there was a leak or draw down somewhere down stream from the PCU. No big surprise there. The black output line to the axles is just one long line that tees off to the front axle and to the rear of the truck and then again at the middle for the first and second rear axles. So I took my pliers and by completely cutting off the line as it went to the front axle, I was able to take this part out of the system. Reset and tried again. Still set 5 flashing light code. So then I went and reopened the front and clamped off the line going to the whole rear system. Tried again and this time the system worked. Now I at least had the 2 front tires working. So next, clamped off only the last rear axle right at where this line enters the last axle's quick release valve. And still the system worked fine. I now was up to 4, and I also then knew the problem was in the last axle. I took the pliers off, went back and tricked the system as a whole to work again so I could observe the last axle for leaks. The system filled up again,exhausted itself, and the solid hwy light went on as it should, but by observing at the rear axle I noticed air was still slowly leaking out of the quick release valve's exhaust port. So I figured the quick release valve was malfunctioning. I replaced that but it didnt fix anything. So I then isolated each side of the last rear axle by first capping off the large lines going from the quick release valve to each end of the axle tubes. By doing this I found that the problem was only in the right side. I re hooked up the left side and now was able to get the system to work with just the right rear axle capped off. Now I was good to go for 5 out of 6! I then decided to put shop air at 70 psi into the right side of the inside axle tube fitting where it was already disconnected to try and find a leak down stream to the tire. The air went through the axle to the wheel valve and into the tire and filled it up to 70 psi without any noticeable problems. So I thought maybe that tire was just too much lower in pressure then the rest and that in itself was setting off the code (At the time also thinking to myself this system really sucks if its that temper mental.) Now that the right rear tire was filled up to 70 psi like all the rest I thought if I re connected it back up to the system, all might just work. I disconnected the shop air line at the right axle so I could connect it back in, and when I did I instantly realized that air would not stop back flowing out of the wheel valve and tire as it should. The wheel valve is supposed to just exhaust itself then shut off. This is to keep the tire from deflating in case this hose fails. So I just replaced the wheel valve on the right last axle, re filled the tire up again with 70 psi shop air, disconnected it this time as before and this time air just came out for a few seconds then the wheel valve shut itself off. So I hooked everything back up and now it all works( at least for now!). At the time I should have realized that the air leaking out of the quick release valve wasn't the QRV itself but actually one of the wheel valves, but I didn't stop and think about it at the time.
Before, every time I went to diagnose the CTIS on this truck or any of the others, I would quickly get frustrated. Mainly because I didn't even know where to start. I could never find any leaks and the air lines running along the frame are so buried,zip tied and bundled together its hard to even start looking. But if you can first isolate the area, it for one gives you confidence, and just by allowing you to get part of the system to start working it is in itself motivating, and it allows you can narrow down the area to pin point the problem. At least thats the way it worked for me.

 

[1 Patriot-of-many]

Good way of doing it and thinking outside the box! Congrats, never saw that method before here!

 

[MO MV man]

Thank you, Hawssie!

That has to be one of the most common sense, easy-to-follow CTIS troubleshooting methods I've ever read.
Outstanding.

 

[Hawssie]

Thanks, she is still working like a charm. In the future I think I will install a 24vdc electric solenoid valve inline to the front tires so I can cut them out of the system when needed. That way I can leave the front tires at my desired pressure and just adjust the rear. And since this truck is a tractor, that way I can dump the rears to get under a trailer easier(poor man's air bags) and also adjust the pressure for the weight. The rears are really the only end I want to adjust according to weight vs ride. I don't want the front aired down like the rears really under any circumstances except for maybe off road.. Now if I could just re program the psi settings, that would really be cool. I also want to install a permanent in dash air gauge for the system so I can see where the pressure is when the system is re filling from one setting to the next. It seems like it would be nice to know where the pressure is while your waiting and give you an idea before you for instance, start driving away with the trailer, as it does take a long time to air up those big tires all at once. Then you would know when its safe to start moving and let it fully fill up while on the road.

 

[hklvette]

FWIW, the wheel valves are easily rebuildable. I have 10 that I'm going to rebuild when I get the chance. The trick is that inside there is a "seat" that the sealing diaphragm presses against that gets rusty with age and water intrusion. They aren't available in the aftermarket channel from DANA, so I'm having some made from 5/16-24 (IIRC) stainless bolts.

 

[jwaller]

I cannot read that gigantic block of text. Can you possibly break it up with maybe a space or two

 

[davo727]

Try this edit


Well I got my CTIS system working now for the first time, And I thought I would describe how I was able to track down the problem(s) just in case anyone else is having similar issues.

First I put a gauge inline at where the black nylon output line comes out of, the cab mounted Pneumatic control valve. On mine the black line is outgoing, the yellow line is incoming. I did this so I could also see what was going on in the system instead of only just listening to it. So after resetting the system I watched the gauge and at system start up, it would air up the line, and would get to about 60 psi then quickly drop down and set the 5 flashing lights.

So I took a pair of hose clamp pliers (the kind you can clamp on a line or hose to collapse it without damaging the line) and in this case using them to just to restrict the air going out of this line and tried again. After a few tries I was able to trick the system and get it to start filling up the tires: After airing up a while the gauge read around 70 psi, the hwy light stopped flashing and the system exhausted itself, the gauge went dead, the hwy light went solid and everything was fine.

But after this without the clamp and turning the truck off and back on again, thus causing the system to re-power up, it again tried to air up but ended in just setting the 5 flashing lights again. So I knew there was a leak or draw down somewhere down stream from the PCU. No big surprise there.

The black output line to the axles is just one long line that tees off to the front axle and to the rear of the truck and then again at the middle for the first and second rear axles. So I took my pliers and by completely cutting off the line as it went to the front axle, I was able to take this part out of the system. Reset and tried again. Still set 5 flashing light code.

So then I went and reopened the front and clamped off the line going to the whole rear system. Tried again and this time the system worked. Now I at least had the 2 front tires working. So next, clamped off only the last rear axle right at where this line enters the last axle's quick release valve. And still the system worked fine. I now was up to 4, and I also then knew the problem was in the last axle. I took the pliers off, went back and tricked the system as a whole to work again so I could observe the last axle for leaks.

The system filled up again,exhausted itself, and the solid hwy light went on as it should, but by observing at the rear axle I noticed air was still slowly leaking out of the quick release valve's exhaust port. So I figured the quick release valve was malfunctioning. I replaced that but it didnt fix anything. So I then isolated each side of the last rear axle by first capping off the large lines going from the quick release valve to each end of the axle tubes.

By doing this I found that the problem was only in the right side. I re hooked up the left side and now was able to get the system to work with just the right rear axle capped off. Now I was good to go for 5 out of 6! I then decided to put shop air at 70 psi into the right side of the inside axle tube fitting where it was already disconnected to try and find a leak down stream to the tire. The air went through the axle to the wheel valve and into the tire and filled it up to 70 psi without any noticeable problems.

So I thought maybe that tire was just too much lower in pressure then the rest and that in itself was setting off the code (At the time also thinking to myself this system really sucks if its that temper mental.) Now that the right rear tire was filled up to 70 psi like all the rest I thought if I re connected it back up to the system, all might just work. I disconnected the shop air line at the right axle so I could connect it back in, and when I did I instantly realized that air would not stop back flowing out of the wheel valve and tire as it should.

The wheel valve is supposed to just exhaust itself then shut off. This is to keep the tire from deflating in case this hose fails. So I just replaced the wheel valve on the right last axle, re filled the tire up again with 70 psi shop air, disconnected it this time as before and this time air just came out for a few seconds then the wheel valve shut itself off. So I hooked everything back up and now it all works( at least for now!).

At the time I should have realized that the air leaking out of the quick release valve wasn't the QRV itself but actually one of the wheel valves, but I didn't stop and think about it at the time.
Before, every time I went to diagnose the CTIS on this truck or any of the others, I would quickly get frustrated. Mainly because I didn't even know where to start.

I could never find any leaks and the air lines running along the frame are so buried,zip tied and bundled together its hard to even start looking. But if you can first isolate the area, it for one gives you confidence, and just by allowing you to get part of the system to start working it is in itself motivating, and it allows you can narrow down the area to pin point the problem. At least thats the way it worked for me.

 

[Hawssie]

Thanks for the editing guys!