M1078A1P2 CTIS Deflating All Tires

[Regular_Forces]

Good morning everyone. I am having issue when starting vehicle all tires simultaneously deflate. I have troubleshoot the CTIS system. Replace ECU, PCU, pressure sensor, and CTIS valve on the wheels verifying it had banjo bolt instead of regular bolts etc. I checked continuity from pressure sensor at the wet tank up to the ECU. Then from the ECU to the control valve. Vehicle does the opposite of how a regular CTIS should operate.

 

[GeneralDisorder]

The DANA diagnostic software is free and will work with your MSD and SWICE kit. You can use it to talk to the CTIS controller and see what it's reading for pressure and if it has any diagnostic codes stored.

 

[Ronmar]

So CTIS cycles and the tires start to deflate? If so, look for an obstruction in the PCU vent line. This line runs from the plastic cover on the bottom of the PCU to a port in the floor. You can disconnect the line at the plastic cover to take that line and floor port out of the equation.

Basically if the PCU cannot vent cleanly to 0 PSI, it will hold the wheel valves open and the dump valves will dump tire air. This is how the PUU deflates, it sends the air to a 6.5PSI relief valve which vents the PCU down to 6.5PSI. Anything over ~5PSI is enough to hold the wheel valves open. The dump valves mimic this 6.5PSI from seen from the truck side, by venting any tire air above 6.5PSI.

Have seen this issue numerous times, Usually due to Mud daubers/insects trying to nest in that floor port where it goes thru the cab floor behind the grill. If that is the case disconnecting that line between floor and PCU bottom plastic cover will allow it to vent to zero. That or your PCU control solenoid is not opening cleanly, but you said you swapped it...

 

[Suprman]

Check the vent line on the pcu case make sure a bug didnt build a nest

 

[veespo91]

If the purge valves are dirty they can get stuck open and vent all the air out, worth checking