CTIS PCU Chattering Then Faults

[DeuceRoadTripper]

Having a problem with a CTIS (M923A2). Start the truck up - dump the air in the tires to "run flat" - this works fine. Go to "Sand" mode and listen to the PCU pulse to fill all tires. This will fill to sand mode pressure no problem. Next go to X-C mode and again listen as the PCU starting pulsing to fill. At some point - I am assuming once the pressure increases to a higher level than "Sand" the PCU starts to "Chatter" (pulsing on/off very fast) as it tries to turn off the air output. If I switch back a fourth from Highway to X-C I can keep this thing filling. But if it starts to chatter and I do nothing after a few seconds ~~> minute of chattering it will simply fault out.

My question is - is this simply purchasing a rebuild kit and replacing the pistons and o-rings seals in the PCU as it works fine to fill to sand just not any higher pressure? Has anyone had a unit do this to them?

 

[Suprman]

Could need new o-rings in the valve body. There are 3 separate solenoid controlled valved in it. It is not hard to take apart you just have to be careful and use a plastic screwdriver when you have it apart and are pushing out the valve plungers. I believe you can use a generic o-ring kit.
Will

 

[DeuceRoadTripper]

Didn't see the part about a generic O-ring in your message. Will take that critter apart and try just replacing the piston O-rings before getting a whole kit. Thank you!


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The valve body I assume your talking about is the PCU (device under the dash) behind the guard plate? I seen a replacement rebuild kit on Erik`s surplus $140 which looks like it includes new pistons O-rings and a plastic cover with seal. Just wondering if that was the correct part to through a little cash at to start fixing this problem. I downloaded the TM for this and see the pistons inside the block. Was hoping for just a single screw on solenoid but it looks like the solenoid is part of the block. Do you know of any other supplier for a rebuild kit?

 

[todds112]

This was the exact symptom I was having before mine quit, and only gives the "5 light flash" error. Did you fix it?

 

[todds112]

Should that little pressure relief valve on the side of the PCU open right away? I took the cover off the PCU so I could watch it and feel around for leaks when it tries to start. As soon as the system hits 120 PSI the CTIS turns on and tries to work. That little relief valve opens right away. Anyone know what pressure it's supposed to open at? Could my CTIS problems be as simple as this little relief valve being bad?

 

[todds112]

I went through the troubleshooting guide again step by step. I checked every single electrical connection checking for continuity and shorts. I finally got to the section on checking the PCU sensor. Everything is pointing to the sensor being bad. Of course, it says if it fails the tests replace it and test again. So the part number is NSN 6695013296418, part# 59960. Anyone have an idea where to get one?

 

[todds112]

Found a PCU sensor. I guess I'll know here in a few days if that was it.

 

[SLOrazorsedge]

I've got the same problem with my M932A2, where did you find the PCU? New or used?

 

[todds112]

I've got the same problem with my M932A2, where did you find the PCU? New or used?

I just ordered a sensor from Those Military Guys. Suprman told me he has good used PCUs. I'm hoping it's just the sensor itself and not the entire PCU.

Check the continuity from the connectors on the PCU back to the ECU connector. I've been told numerous times there is a propensity for the wires to break right at the sensor connector. Mine all checked OK, which leads me to the sensor itself. Hope I'm right. The flow chart on Page 32 of the Dana CTIS troubleshooting guide indicated that. I haven't found a way to bench test the sensor anywhere.

 

[todds112]

Nope, new PCU sensor didn't fix it.

 

[jrosbo]

Sounds kinda like what mine was doing. I ended up replacing a solenoid and it fixed the problem. If you do a search on here there is a thread on how to check the solenoids and what kind of solenoids to get. They are easy to replace and they are not expensive. I paid less then 20 bucks for three of them from a popular auction site,

 

[todds112]

Sounds kinda like what mine was doing. I ended up replacing a solenoid and it fixed the problem. If you do a search on here there is a thread on how to check the solenoids and what kind of solenoids to get. They are easy to replace and they are not expensive. I paid less then 20 bucks for three of them from a popular auction site,

I actually have 3 new solenoids on my desk. The ones in the PCU all tested OK on continuity and resistance, though. I don't know if they could be bad even if those tests were OK?

 

[jrosbo]

Two of mine checked good. In the high range. One was in the lower part of the range. I was out of ideas so I went and replaced it and it fixed my problem.

 

[todds112]

Well I went ahead and replaced the solenoids with the new ones. Had the same results, straight to 5 light flash. Now for the really dumb thing I did. When I first took the PCU apart and cleaned it (weeks ago), I removed the 3 solenoids. I failed to note which one went where. So I looked in the TM and saw the order for them. They are labeled D-S-C. I put them back in the way the TM showed. Today while sitting and staring at it, after it still didn't work, I noticed there is a S-D-C molded onto the top part the PCU where the hoses attach. That wasn't the order that was shown in the TM for the solenoids. So I took it apart again and switched S and D to match the markings and low and behold the CTIS started working! Now it worked fine for about 30 minutes, then starting chattering again. It doesn't go to an error flash though. I also found a lose fitting on a rear CTIS valve, the big nut that tightens down on the tube coming from the hub. I was so tired by this point I quit. Not sure what its current state is. I'll take it for another drive tomorrow and see.

 

[SLOrazorsedge]

So it looks like I just need to replace the 3 solenoids to avoid the back and forth chasing? Where did you source your solenoids from? My truck worked perfectly from time of purchase until winter weather dipped down into the 20's. I thought it might be condensation freezing in the system however no love once the weather warmed back up.... :0(

 

[todds112]

http://www.steelsoldiers.com/showth...oid-replacement&highlight=solenoid+replaceent

Here's a good thread on it. That's where I got mine.

Unfortunately, due to my screwed up methodology I don't know if it was the solenoids, the PCU sensor, or the leaking connection on the wheel! It might have been a combination of all of them. It did click a few times with the new electronics, so that part might have been the leaky connector. Took her out today and its working just as it should. I guess we'll see for how long!

 

[Alexsha]

Glad my info helped.

 

[DeuceRoadTripper]

Resolve to possible chattering effect on pneumatic controller: Check for low supply air pressure to CTIS system.

The gauges on the dash of the M923A2 are direct to the tanks. They do not reflect the supply pressure in the CTIS system. Typically the CTIS main air supply to the pneumatic controller is regulated to 65 PSI by a pressure regulator located on the top of the fire wall mid center under the hood.

This pressure regulator is connected to the vehicles main air supply, regulated down and then sent inside the cab to the passenger side, through a water catch to the pneumatic controller supply port.

If the supply air pressure is below 65 PSI – the CTIS system simply cannot obtain highway pressure and the pneumatic controller will “chatter” for a moment before the ECU faults out with (5 flashing) lights.

The supply line from the regulator under the hood is copper to the inside. However, after the water catch should be plastic pneumatic tubing. Install a pressure gauge inline to visually verify the pressure at the manifold is at least 65 PSI. If it is low, try bypassing the water catch first (it might be plugged). Then adjust the regulator to increase the air pressure if it is still low. A small change might give a large increase in supply. If so, turn back the regulator to 65 PSI. Cycle the system again.

 

[todds112]

Are you referring to the governor on the firewall? That doesn't govern air pressure to the CTIS. It governs the air sent to the wet tank, by cycling the compressor unloader valve. It also signals the air dryer valve to expel. It is set around 125 PSI. Some have raised it a bit to help the CTIS system because the pressure switch (electrical) that activates the CTIS system turns on at 120 PSI. I'm guessing the 65PSI number you are getting is from the pressure protection valve that connects the wet tank to the auxiliary air system. This valve basically requires 65PSI in order for the auxliary system (which includes CTIS) to receive air pressure. Once that valve does open, the pressure sent to the CTIS will be equal to the pressure in the wet tank. In some trucks the highway tire pressure is 70 PSI, so having the CTIS input governed to 65 PSI wouldn't let the tires fill up from the get-go.

 

[DeuceRoadTripper]

Yes, your correct. My mistake...