CTIS PCU Deflate Solenoid - Connector Unplugged; faulty wiring or solenoid

[charlesrg]

My CTIS is not inflating the tires so I went to check with the computer and I found PCU Deflate Solenoid - Connector Unplugged ; Fault Wiring or Solenoid.

Does anybody knows if there is a CTIS troubleshooting guide or have seen this before ?

I'm suspecting that my ABS light is related to this.

 

[Ronmar]

suspect it will have no relation to ABS... PCU is under the passenger dash, check the connector, and use a ohm meter to ring out the 3 solenoid circuits...

 

[GeneralDisorder]

The CTIS sub harness wiring is probably boned. Look for green crusty corrosion on the various connectors. And ABS light may in fact be related as the CTIS wiring could be taking down the communication busses which will piss off the ABS module. Check for shorts to power and ground and other wires in the CTIS harness but I have seen that - water gets in through the cab marker lights or the windshield or the turret cover and causes damage to the CTIS sub harness that runs behind the HVAC and over to the PCU.

Also the ABS is easy - get the WABCO software and speak to the controller to get the codes from it.

 

[charlesrg]

I got able to fix all ABS bus problems, I had a missing terminator (cut off) and a burnt terminator. Then found that the front ABS connectors were rot.

Now I still have an issue with CTIS, it's saying "shut off failure - cannot close wheel valves and vent lines. "

Air is leaking from this valve.

 

[Ronmar]

Where exactly is "this valve" located? That is a Quick reacting or dump valve, there is one for each axle(services 2 wheels). it has one input port and 2 output ports(one for each wheel), and a vent port.

These are remote pressure regulators whatever is applied to the input port the valve mimics on the output ports by passing input air to output, or if the input pressure is lowered, the valve will vent air from the output ports thru the vent. the only way air can come out of the vent port is if it is coming from a wheel...

if air is coming out of that vent port, and CTIS is not doing anything, you most likely have a leaking wheel valve... If the CTIS has the system pressurized and air is leaking out that vent, you most likley have a leak somewhere, lowering the truck side input pressure and the dump valve is doing its job matching output to input by venting tire air...

The code you mentioned, deflate circuit unplugged/open indicates a wiring issue with that solenoid coil located under the plastic cover on the bottom of the PCU under the passenger dash. It shares a common connector with the other 2 solenoids(control and supply) thru the side of that plastic cover...

Typically most all CTIS issues are either leak or flow related...

 

[charlesrg]

The valve is on the frame under the truck. I will take a better picture tomorrow during daylight.

When I turn on the truck the Front tire driver tire and the middle driver tire start to get inflated to 70psi (pressure set on the CTIS) , when they reach 70 psi I hear the air system purge valve and then I hear the tires getting deflated. The cycle repeats and repeats. The tires go down to around 45-50psi and again the system re-inflates then.
If I turn off the truck this two tires get deflated and then the valve closes leaving the tires at around 40-45 psi.
I'm guessing is something with the CTIS shut off valve

 

[GeneralDisorder]

Nope. You just need new wheel valve diaphragms. That's what they do when they get old and hard. They get progressively worse at holding pressure and the controller will keep trying - it will fault out after 10 tries. It's inflating but the wheel valves don't hold pressure so when it waits one minute after the inflation cycle, and then does the confirmation check, the pressure has dropped below the desired setpoint and it goes back into another inflation cycle.

You should rebuild or replace all the wheel valves and throw a kit in the PCU. Check those two off your list and then report back if you still have issues.

 

[Ronmar]

What general said. The wheel valves are leaking… bad or dirty diaphragms.

Everything after the PCU is controlled with air pressure and flow. The front axle dump valve is on the right side of the transmission. The dumps for the rear axles are on the crossmembers above those axles.

when CTIS cycles it seals the system(closes control solenoid) and gives a brief shot of supply air(supply solenoid) from the wet tank. This pressurizes the system above 5PSI. The dump valves send this pressure to the wheels which is enough to open the wheel valves. This connects all wheels with the PCU and the controller looks for a stable pressure on the pressure sensor located on the PCU. Here is where one particularly low tire can cause a fault, because as soon as the low tire is connected with the other fuller tires, the pressure try's to equalize . This can cause an unstable reading and the controller faults. Usually a few cycles will equalize the pressures enough that the controller gets an acceptable pressure and either adds air, releases air(deflate solenoid) or calls it good and releases the control solenoid.

releasing the control solenoid vents the PCU to zero pressure. The dumps see this on their input and mimic it on the wheel side output ports. As the wheel pressure falls below 5PSI the wheel valves should slam shut, so the dump valves all vent briefly. If it continues to vent 1 of 2 things is likely happening, wheel valves as General mentioned are not re-sealing, or there is a restriction somewhere that is preventing the pressure from dropping cleanly below 5PSI and the tire pressure continues to feed the dump valve which continues to vent the air until the decreasing tire pressure cannot feed enough air to keep the truck side of the wheel valve over 5PSI and it closes.

This has been a fairly common issue I have helped troubleshoot with the main PCU vent being clogged by insects. When the controller ends a cycle it opens control but the system does not cleanly vent below 5PSI because of the clog and proceeds to deflate all the tires until the flow out of the tires finally gets low enough to allow the truck side pressure low enough for the wheel valves to close.

if it is a single wheel on an axle, probably a wheel valve. If it is 2 wheels on an axle it could be a dump valve sticking or a clog associated with that dump. Or both wheel valves on the two wheels… all wheels, probably a clog on the main vent line out of the PCU or a sticky PCU control valve.

put a jack stand under the axle at the wheel you are working on and let the air out of the tire. Remove the 4 screws on the wheel valve to access the diaphragm and a spring. Behind the diaphragm, you will find a small hole in the center that is where the rubber diaphragm seals the port into the tire(center hole). clean the center seat around that hole and you most likely need a new diaphragm. I had one wheel that leaked and the diaphragm was fine, just some crap fouling the center hole…

good luck!

 

[charlesrg]

I've been checking for leaks at each valve, I placed gloves on each and checked pressure, they did not leak at 70 psi.
If I turn off the CTIS or disconnect from the banjo bolt they remain inflated.
@Ronmar please do you know where can I find the PCU vent ?

I'm trying to find the diagram for the system but no luck so far.



So far I've found this diagram TM 9-2320-366-34-2 - Page 1403

 

[GeneralDisorder]

PCU vent is on the side of the PCU. Earlier models have the vent routed to behind the grill. Newer models have it just vented under the dash.

You should rebuild the PCU.

 

[Ronmar]

That is the best way to check for wheel valve leaks. so they look OK to 70 PSI by your testing

The top half of that diagram is a CTIS plumbing diagram found on a 6X6 truck. you probably do not have the kneeling valves shown on the front wheels at the extreme left as they were discontinued, and the front dump valve is physically located to the right side of the transmission tucked into the passenger frame rail...

What General said about the vent. the PCU control valve vents into the bottom plastic cover and on earlier trucks they connected the plastic cover to a floor pass-thru port that vents the air behind the grill. on later model trucks, they just vent from the plastic PCU cover into the under-dash area.

The PCU valves are pilot operated valves. IE: a small solenoid valve uses a little air to control a larger bore valve core to move a bunch of air. their Orings can go bad, or simply become fouled. i have a pic of one disassembled and the valve spools were full of what looked like air dryer/filter media(looked like large beach sand/salt crystals). If you take out the PCU, remove the bottom cover you will find 6 allen head bolts that will allow you to split the PCU valve block to access the 3 internal valve spools. you can use a pic or a scribe to work them up out of their holes to at the very least clean and inspect them.

If i recall correctly Superman, a member and supplier here on Steel Soldiers had the overhaul kits. they are fairly easy to pull apart and work on...