CTIS pressure settings increase - no programming, transducer, or module required.

[M1224]

Heck yeah! Let us know what you find!

I have to replace the Pressure Transducer first so the system can read tire pressure again, then I'll start playing with it. Anyone know the PN for the P110 pins?

 

[Awesomeness]

Do the M939 CTIS controllers work without modification in the LMTV A0's? I know the A1 can talk to it, but the A0 can't. Has anyone used one?

 

[GeneralDisorder]

Do the M939 CTIS controllers work without modification in the LMTV A0's? I know the A1 can talk to it, but the A0 can't. Has anyone used one?

Since the A0 doesn't have a J1939 bus at all I would *assume* it would work without issue. The only issue with them on the A1 trucks is they burn out the J1939 termination resistors if you don't pull the pins out of them. Not having those pins doesn't affect their operation though - seems that Dana left some pins hot that they assumed wouldn't ever be used and those ended up being the pins they later used for the J1939 so it kinda broke the forward compatibility unless you know to pull the pins out or disconnect the wiring to them.

 

[hike]

Do the M939 CTIS controllers work without modification in the LMTV A0's? I know the A1 can talk to it, but the A0 can't. Has anyone used one?

As @GeneralDisorder does, I *assume* the M939A2 CTIS ECU will plug and play in the LMTV A0 variants. Easy enough to check. Use the M939A2 CTIS schematic from post#65 and match to your A0 schematic?

 

[M1224]

Well, looks like I have a lot more work. I used the jumper wire method to check for leaks, and as soon as I jumped pin B to open the wheel valves, the tires started deflating out the dump valve. Time to pull the PCU and go through it. I did get Pin M switched to Z, so I'll have 81 psi highway when it's back together. then I can work on the switches.

 

[GeneralDisorder]

Well, looks like I have a lot more work. I used the jumper wire method to check for leaks, and as soon as I jumped pin B to open the wheel valves, the tires started deflating out the dump valve. Time to pull the PCU and go through it. I did get Pin M switched to Z, so I'll have 81 psi highway when it's back together. then I can work on the switches.

That happened the first time I powered up my system too! I did manage to get it to stop fortunately so I could drive home from @Lostchain 's shop. PCU spool valves were contaminated with crap from the wet tank. They really should have given the PCU an inline filter so crud from the wet tank wouldn't get into it.

 

[Ronmar]

Yep, classic leak. Give a shot of air to open the valves then it dumps tire air trying to match the system pressure drop caused by the leak. Thats the same way the system deflates. They connect the system to a 6.5PSI relief valve(leak) that drops the truck side of the system down to around that relief pressure and the dumps try and match that pressure in the tires By venting tire air.

Best way to trouble shoot this IMO is to disconnect the PCU output line and connect a regulated air source, say 60PSI, to that line feeding down to the dump valves and the wheels. Then you can hold all the plumbing around that 60PSI indefinitely while you go over all the plumbing And axle vents looking for the issue… find nothing there? Then the control or deflate valves in the PCU are leaking…

Mmmm PCU valve crap… Mix that with a little garlic and some butter and it makes a pretty good steak seasoning

 

[M1224]

The green controller is not triggering the control valve or the fill valve for the initial pressure check, and once that process fails, I get 5 flashing lights. The harness and tank sensor pass checks, I ran down the entire TM electrical troubleshooting procedure. TM says Transducer is bad, but if the computer isn't even cycling the valves, there's nothing for the Transducer to read.

I'm going to do the regulated air supply at 55psi and test for 2.5v at the Transducer as well as the standard leak checks. I have a feeling it's time to collect about a dozen green boxes and just keep trying them out till I find one that works.

 

[Ronmar]

Well yes there is something for it to read, with control open the manifold that the sensor is connected to is open to the atmosphere. Thats its first check, can it see atmospheric pressure… If it cannot see that it will not proceed…

have you had the PCU sensor out? They installed it pointing straight up, which is usually considered poor form for sensor installation because they can collect crap…

Don't have these issues using 2 switches a relay and a pressure gauge. At this point in my life I think I can live without a black(or green) box checking my tire pressure every 15 minutes...

 

[M1224]

Well yes there is something for it to read, with control open the manifold that the sensor is connected to is open to the atmosphere. Thats its first check, can it see atmospheric pressure… If it cannot see that it will not proceed…

That's probably the main issue then. When powered, it reads 00.00 Volts. Test failed, 5 flashing lights.

have you had the PCU sensor out?

Not yet. Doing that today.

They installed it pointing straight up, which is usually considered poor form for sensor installation because they can collect crap…

The slight angle they put it at was a sorry attempt to compensate, but was never enough to do any good.

Don't have these issues using 2 switches a relay and a pressure gauge. At this point in my life I think I can live without a black(or green) box checking my tire pressure every 15 minutes...

Once I start updating the configuration, adding in the AC and audio (and an interior light), I'll start tackling the manual CTIS conversion.

 

[Lostchain]

I have a feeling it's time to collect about a dozen green boxes and just keep trying them out till I find one that works.

It would be the proper course of action to simply ask the controller you have what is wrong with the system, and then repair from there. Dana Diagnostic Tool and a J1939 adaptor is what’s required for this.

 

[M1224]

It would be the proper course of action to simply ask the controller you have what is wrong with the system, and then repair from there. Dana Diagnostic Tool and a J1939 adaptor is what’s required for this.

Except the J1708 and J1939 are not pinned in the CTIS harness. My truck has a J1708 Diagnostic plug, but only the Trans is connected.

 

[Lostchain]

Except the J1708 and J1939 are not pinned in the CTIS harness. My truck has a J1708 Diagnostic plug, but only the Trans is connected.

Might be more work than you want to do but the pins are present in the controller, and if you already have a J1708 port for the transmission, might make sense to just run the CTIS 1708 over there so you have access to both controllers. The DDT is just the right tool for the job on CTIS. It works just as good (only slightly slower) on the low speed bus.

 

[ckouba]

Don't have these issues using 2 switches a relay and a pressure gauge. At this point in my life I think I can live without a black(or green) box checking my tire pressure every 15 minutes...

Yeah, what Ron said... LOVE my two switch system. No regrets and completely reversable.

 

[M1224]

OK. I received my new Transducer. So I decided that while I was in there I may as well rebuild the PCU. New O-Rings everywhere and a light coat of silicone lube. New transducer installed.

Got everything hooked up, all 4 tires at 60 psi, wet tank full.... I plugged in the controller, and everything started working. And as soon as it pressurized the lines and opened the wheel valves, the rear dump valve started draining the tires. Soon as the control valve closed, it stopped. Now I have a Highway and Run Flat flashing situation. I thought maybe the deflate valve may have been stuck open, but it's not.

So, why only the rear dump valve and not both front and rear? Possibility the rear dump valve is stuck open?

 

[Ronmar]

You probably have a leak on the line between the T fitting at the transmission and the rear dump valve. The front axle QR valve(beside transmission) is also probably dumping, just not as loudly... Since the controller cycles rapidly it is hard to track leaks. Either jumping the plug for control and giving a shot of supply, or disconnecting the PCU output line and connecting a regulated air source to that line at say 55-60PSI to hold the system at pressure is the best way to track CTIS leakage.

If you use the regulator on the CTIS output line and find all the leaks and the system will set at the regulated pressure but you have issues when you reconnect that line to the PCU, it is probably the problem...

 

[M1224]

disconnecting the PCU output line and connecting a regulated air source to that line at say 55-60PSI to hold the system at pressure is the best way to track CTIS leakage.

Only problem is, with the dump valves open, I don't have a compressor strong enough to keep up and hold that much pressure in the lines.

 

[GeneralDisorder]

Only problem is, with the dump valves open, I don't have a compressor strong enough to keep up and hold that much pressure in the lines.

They shouldn't open with a regulated supply at 55 psi going into their control line and if they are venting they would be venting *tire* air not air from your compressor. That should inflate the tires (if they are low) to that pressure and stop - if they are higher than 55 the air from all the tires will mix and equalize...... The QRV's just replicate to the wheels whatever pressure is sent to them. If one is open and the tires are still deflating on that axle then there's some kind of partial blockage keeping the pressure between the valve and the tires artificially low or a leak before the valve that is artificially dropping the pressure on the QRV control port.......

......yes it's quite the mind game wrapping your head around how they function isn't it?

 

[Ronmar]

Yea they probably won't dump with a regulated air supply making up air. The reason they dump with the controller is that it closes control and only gives a brief shot of air to open the wheel valves and then it looks to measure tire pressure. Of course the leak creates unstable pressure and the unit faults.

The leak dumps system air and the QR valves try and match that pressure drop by dumping tire air. If the compressor makes up most of the air flowing out the leak, the tires shouldn't dump much. Hand over hand the lines and find/fix your major leaks, then break out the bubble mix to find and fix the little ones

 

[M1224]

..yes it's quite the mind game wrapping your head around how they function isn't it?

Good god is it ever. I can't wait to get it all fixed.

Hand over hand the lines and find/fix your major leaks, then break out the bubble mix to find and fix the little ones

That's my project for this weekend.