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You sure can make the changes; But if the PCU has a 12 psi relief valve, the system will not deflate below 14 psi so setting the emergency pressure to 10 will not work. Setting the tire pressure to 100 will not work. Setting the overs peed's too high could be dangerous.

CTIS ECUs can have as many as 8 different variants stored in them. Depending on how Pins (Z) and (M) are wired (High, Float, or Ground) The ECU will load the parameters on power up. (Float Float) may be set for a 4x4 and (High, Gnd) may be set for a 6x6 Heavy. There other parameters in these...

The system calculates the inflation time based on tire volume, 4 vs 6. I think the 6x6 wrecker setting for Highway is 82psi which could have the cold temp issue. If the system is cycling due to cold you can vent the wheel valve cover screw and re-tighten, this will reset the valve to the ambient...

https://www.steelsoldiers.com/showthread.php?175911-Central-Tire-Inflation-System-(CTIS)-AXTS-0015-2018 You cannot replace a 939 ECU with an FMTV ECU. Older FMTV ECUs use J1708 and newer ones use both 1708 and 1939. Changing a trucks CTIS configuration is not recommended. It could generate...

You can make pressure adjustments but if you go too far the system will not function correctly. Valves will not close at high tire pressures in the cold and may not deflate farther then designed.

Novram no battery.

They are all potted...

Never Happen! The connector key is pretty reliable and the circuit is tested for reverse voltage and large power spikes. They simply get old and the capacitors in the power supply start to leak.

That is a bad ECU period end of story.............Sorry.

One of two things; check the starting tire pressures and when is stops, if it did not deflate more than 5psi it will log a "between modes" fault (filters). Or, the deflation relief valve on the PCU (brass valve) is out of range stuck or dirty will log a 2 light fault.

You are correct about the leak, there should be no audible air during an inflate. Two flashing lights means the system is stuck between two modes and is not inflating fast enough. I like to use shop air plumbed to the wet tank to check for leaks. if you don't have >115psi to close the pressure...

The ECU is fine it doesn't like something from the pressure transducer. Follow the procedure in the guide. https://www.steelsoldiers.com/showthread.php?175911-Central-Tire-Inflation-System-(CTIS)-AXTS-0015-2018

It is good that you have a vent valve to dump the pressure to atmosphere so you are not running the air seals continually pressurized. How does this setup handle a deflation?

The front QRV is mounted on the right side frame rail so there is allot longer tubing to get to the left hub. That extra tubing make it harder for the valve to close at higher tire pressures and it get's worse as the valve diaphragms get's colder. Messing with the transducer supply current may...

The sensor is a atmospheric or PSIA so normal atmosphere it puts out roughly .573 volts at .039psi/volt. Say 80psi = 3.12v. If you put in a "Resistor Divider" designed to reduce the signal wire voltage by 10% the system will see 80psi tires as 72psi and what it thinks is now 80psi tires would...

Both PCUs are interchangeable but the pressure sensors are not. you would have to swap the sensor keeping the original, the square sensor require a standoff in the LMTV body to fit.

If the system comes and flashes Highway one time and then 5 lights without checking the tire pressures it doesn't like the atmospheric reading from the pressure sensor on the PCU. Connector pins, wiring, the +5 volts from the ECU. There is a link to the manual a couple of posts back. If the...

www.steelsoldiers.com/showthread.php?175911-Central-Tire-Inflation-System-(CTIS)-AXTS-0015-2018

QRVs are pretty bullet proof. Run Flat light is looking for large tire pressure imbalance >30 to 50% but a upper air line leak can fool the system into thinking it has the imbalance.

Two things can cause the wheel valves to dump air when trying to inflate. The pressure between the PCU and top of the QRVs is not getting above the tire pressure. Big line leak, pressure switch failed closed allowing the system to function with too low of supply air. Second if there is a big...