M923A2 CTIS Problem

TexAndy

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Bee County, Texas
This thread is awesome. Was able to at least rule out my low pressure switch as a problem.

Symptoms: Truck flashes Hwy as normal on startup. Attempts to operate when pressure reaches 120 (or when I jumper pins A and B on that circuit). PCU in cab makes an operatey type noise and then I hear a quick elephant noise from the little rubber duckbill things as the quick spurt of air parts the rubber lips (was able to film it on my smart phone to tell that was what was making the noise), then the 5 lights on the ECU start flashing. When the low air switch is disconnected, it won't even do this self test.

As far as I can tell, there's no axle air seal leak. Or if there is, it's so slight as to be unnoticeable. At least, I can't see, hear, or feel any air escaping out of the little spring-loaded axle vent caps. What's the best way to tell if I have such a leak? I may just not know what to look at/for.

My wheel valves don't appear to be leaking, but I haven't really submerge tested them, yet.

The dana pdf people linked here indicates 5 lights is an electronic issue. So what is my next likely culprit? PCU? Another poster earlier indicated that his problem was bad solenoid(s) on the PCU.

Any thoughts to move me forward without just buying parts would be most appreciated.

Edited to add: Passenger front tire had a two piece rim o-ring seal leak a month ago. Had that fixed and from about 5 weeks ago to yesterday, it didn't leak a single psi with the CTIS wheel valve disconnected and just a regular valve stem core in it. Yesterday, I took the valve stem core out and hooked the ctis wheel valve back up and the tire was completely deflated, today. Didn't hear or see any air escaping from the wheel valve or any connections to it, but that is clearly a leak source. Not sure if that would cause the symptoms I'm seeing.
 
Last edited:

CARMAN

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The elephant noise and all flashing is caused by the ctis running a check, finding a problem, blowing off and then going into error mode ( I believe I’m correct on this ). In my previous post on the last page it was the valves pushing off the posts that caused this. I have a short term fix to keep them from being pushed off but feel there may be blockage in the hubs causing the air pressure to push the valves off. Wondering if running any type of lube through the whole system would help keep things fresh??
 

TexAndy

Active member
1,426
14
38
Location
Bee County, Texas
The elephant noise and all flashing is caused by the ctis running a check, finding a problem, blowing off and then going into error mode ( I believe I’m correct on this ). In my previous post on the last page it was the valves pushing off the posts that caused this. I have a short term fix to keep them from being pushed off but feel there may be blockage in the hubs causing the air pressure to push the valves off. Wondering if running any type of lube through the whole system would help keep things fresh??
Great question for one of the designers of the system. My gut feeling is to avoid using lube to be on the safe side. Aside from maybe on parts you can directly apply it to and wipe away the excess. But it goes without saying, I'm only just starting to learn how this system works.
 

Stellaevil

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4
8
Location
Michigan
Great question for one of the designers of the system. My gut feeling is to avoid using lube to be on the safe side. Aside from maybe on parts you can directly apply it to and wipe away the excess. But it goes without saying, I'm only just starting to learn how this system works.
I apologize, CTIS threads have been slow lately so I do not check as often.
Duck bills are not necessary if the CTIS functions on a regular basis. They can be a real problem in very cold temps because they stick shut or or don't open far enough. A system that faults out after a pressure check is not electrical, it is based on the tire pressure reading only.
#1 cause; An air leak big enough to cause a 5 light fault will be if a tire pressure reading is < 5.0 psi, open air line or axle seals. Remember axle seal leaks out the axle vent when the system checks or inflates.
#2 The PCU may have a sticking solenoid, but you should hear blowing out the "PCU" vent during the entire pressure check. You could block off the air line at the PCU and the system should read the tires at 120 psi then go to a solid light. Then go find the air leak.
 

Stellaevil

Member
97
4
8
Location
Michigan
The elephant noise and all flashing is caused by the ctis running a check, finding a problem, blowing off and then going into error mode ( I believe I’m correct on this ). In my previous post on the last page it was the valves pushing off the posts that caused this. I have a short term fix to keep them from being pushed off but feel there may be blockage in the hubs causing the air pressure to push the valves off. Wondering if running any type of lube through the whole system would help keep things fresh??
Any blocked air passage could only cause a higher than normal tire pressure reading. If air gets trapped in the system after a Vent, the wheel valves may not close properly and start dumping air.
 

Stellaevil

Member
97
4
8
Location
Michigan
I'm guessing this wheel valve is toast?
You can clean all the parts with a mild solvent. If you then massage the rubber diaphragm with oil it may become playable again and work.
You may be able to order the Diaphragm; Dana or Spicer 599805 from a truck parts dealer.
 

Stellaevil

Member
97
4
8
Location
Michigan
This thread is awesome. Was able to at least rule out my low pressure switch as a problem.

Symptoms: Truck flashes Hwy as normal on startup. Attempts to operate when pressure reaches 120 (or when I jumper pins A and B on that circuit). PCU in cab makes an operatey type noise and then I hear a quick elephant noise from the little rubber duckbill things as the quick spurt of air parts the rubber lips (was able to film it on my smart phone to tell that was what was making the noise), then the 5 lights on the ECU start flashing. When the low air switch is disconnected, it won't even do this self test.

As far as I can tell, there's no axle air seal leak. Or if there is, it's so slight as to be unnoticeable. At least, I can't see, hear, or feel any air escaping out of the little spring-loaded axle vent caps. What's the best way to tell if I have such a leak? I may just not know what to look at/for.

My wheel valves don't appear to be leaking, but I haven't really submerge tested them, yet.

The dana pdf people linked here indicates 5 lights is an electronic issue. So what is my next likely culprit? PCU? Another poster earlier indicated that his problem was bad solenoid(s) on the PCU.

Any thoughts to move me forward without just buying parts would be most appreciated.

Edited to add: Passenger front tire had a two piece rim o-ring seal leak a month ago. Had that fixed and from about 5 weeks ago to yesterday, it didn't leak a single psi with the CTIS wheel valve disconnected and just a regular valve stem core in it. Yesterday, I took the valve stem core out and hooked the ctis wheel valve back up and the tire was completely deflated, today. Didn't hear or see any air escaping from the wheel valve or any connections to it, but that is clearly a leak source. Not sure if that would cause the symptoms I'm seeing.
Sorry need to be more clear. 5 light fault before the pressure check = Electrical short or open, after the pressure check = <5 psi tire pressure reading. If the system starts to inflate or deflate and there is a problem it may take 20 minutes or more for the system to see there is a problem.
 

TexAndy

Active member
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14
38
Location
Bee County, Texas
Sorry need to be more clear. 5 light fault before the pressure check = Electrical short or open, after the pressure check = <5 psi tire pressure reading. If the system starts to inflate or deflate and there is a problem it may take 20 minutes or more for the system to see there is a problem.
When I start the vehicle, it flashes HWY only for a few minutes until the first pressure check. Then it does the pressure check, I hear air noise briefly at the PCV, elephant noise in the back, then it goes to 5 flashing lights.

I tried airing all the tires up to 75 psi manually. Still no luck.

Where can I find the vent on the PCU? I want to try holding my hand over it to make sure that's working properly when it does a pressure test.
 

Jbulach

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My bets on a leak. Spray a thick mix of soap water on the wheel valves, especially the rears where they connect onto the adapters. Did you try hitting the runflat button to see if it will continue to try inflating?
 

TedCat

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Saline Mi
I would check your air pressure switch with multimeter, also make sure all the solenoids are clicki g. The cover comes off pretty easy and you should feel one click to open the valves. The other clicks for inflate and the last for deflate. I have extras if you find one bad. There is a good thread somewhere around here on test the PCU with mumtimeter at the plug. I found that to be helpful.
 

Grond

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Location
Utah
If you hear no solenoid clicking, then it is waiting for system air pressure to reach 100psi. As the sensors age, this slips. Set your truck air pressure to 120psi, and try it. Most of these truck will not be able keep up with filling at an idle, bit will do it quickly at speed.
how do you adjust the air pressure up this may be whats wrong with mine
 

Grond

Member
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20
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Location
Utah
I would check your air pressure switch with multimeter, also make sure all the solenoids are clicki g. The cover comes off pretty easy and you should feel one click to open the valves. The other clicks for inflate and the last for deflate. I have extras if you find one bad. There is a good thread somewhere around here on test the PCU with mumtimeter at the plug. I found that to be helpful.
do you have a part number for a solenoid I am getting no clicks in the cab or air
 

74M35A2

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Air pressure governor on the firewall, pass side, underhood. Canister looking ordeal with 3 or so air lines to it. Adjustment is on end, under cap.
 

galaxie428

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Location
Rushville, IN
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?
 

Grond

Member
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20
8
Location
Utah
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?
I just tightened the nut down on mine but mine was pretty much loose to begin with but it stopped the leak.
 

CARMAN

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On a thread somewhere...maybe this one, I had mentioned that my 923 does the same thing. Seems to get more picky as time goes on. BUT...when I first crank er up, I have to idle it up so it does not do the pressure check and then dead duck then 2 or 5 light flash. So idle up to 1200. Let the truck warm up and air up. For some reason it prevents mine from going nuts and I as well can find no leaks. Been all over with soap.
 

Jbulach

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Hi all. I have had my M923A2 for a little over 4 years with a perfectly good working CTIS. Recently I started getting the 5 lights flashing after some time of the system trying to fill up. It is too cold out to try to do much trouble shooting right now but I did take the truck for a drive yesterday. I aired down to emergency while slowly driving on the back roads. Once it aired down to emergency, no flashing lights. I aired up to x-c and once it hit it, no flashing lights. I put it back on hwy and got the 5 flashing lights again. I checked the tire pressure with a gauge when I got home and both the front and middle axle tires were all at 50PSI, the back axle, both tires were at 40 PSI. I also noticed that the quick release valve on the drivers side rear over the rear tires was leaking what seems like a significant amount of air out of the port that has a dust cover on it. The dust cover is dry rotted but not sure that really matters. If it ever warms up a bit, I would like to start troubleshooting and fixing this. Thoughts on where to start? Thanks.

View attachment 754530
Do you have a tire, or two that goes down over time? Ditch the rotten dust cover on the QR valve. Inflate all the tires to the same pressure, then see if the QR valve still exhausts while attempting to fill the tires. If it does, pull it off and check for debris in the rubber flap, or the flap maybe rotten as well and need replaced.

If you have a low tire on one axle, the CTIS will actually dump air from the other two axles out their QR valves until all three axles pressures have balanced. Running at high idle while filling helps tremendously if you have small leaks, or a tire with lower pressure than the rest.
 
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