M923A2 CTIS Problem

[cbrTodd]

Thanks, guys. I'll try jumping the A and B terminals tonight and hopefully report back with success.

 

[phxmark]

The correct one will have two wires coming out of it. It will go to a Canon connector connected to about six feet of harness coiled under the truck and zip tied up. I thought my pressure switch was bad, so I ordered a new one. It actually turned out the Canon connector was bad. I just took the Canon connector out and spliced in a waterproof automotive plug I purchased at the local auto store.

 

[cbrTodd]

Tonight I did more troubleshooting on my truck and confirmed that the 3 wire sensor is indeed the CTIS pressure switch. Apparently some trucks have 2 wire sensors and some have 3. The Dana .pdf I was looking at last night didn't have any troubleshooting information in it, but I found one today that confirmed either style switch might be used.

Tonight the CTIS acted like it was intermittently trying to work but only when the air was at its peak pressure, so I adjusted my air governor up from just above 120 psi on the primary tank to ~128 psi (top end of the spec listed in the TM) and it seems happy again. Last night I had no continuity between any 2 of the 3 terminals of the switch with the truck running and 120 psi in the tanks. Tonight, with 128 psi in the primary tank and the truck turned off, I was able to confirm continuity between terminals A and B.

So either my pressure switch drifted higher or my air governor drifted lower. Regardless, it's behaving fine for now, and I know which terminals to jumper should I ever need to do so.

Thanks again, guys!

 

[Stellaevil]

Tonight I did more troubleshooting on my truck and confirmed that the 3 wire sensor is indeed the CTIS pressure switch. Apparently some trucks have 2 wire sensors and some have 3. The Dana .pdf I was looking at last night didn't have any troubleshooting information in it, but I found one today that confirmed either style switch might be used.

Tonight the CTIS acted like it was intermittently trying to work but only when the air was at its peak pressure, so I adjusted my air governor up from just above 120 psi on the primary tank to ~128 psi (top end of the spec listed in the TM) and it seems happy again. Last night I had no continuity between any 2 of the 3 terminals of the switch with the truck running and 120 psi in the tanks. Tonight, with 128 psi in the primary tank and the truck turned off, I was able to confirm continuity between terminals A and B.

So either my pressure switch drifted higher or my air governor drifted lower. Regardless, it's behaving fine for now, and I know which terminals to jumper should I ever need to do so.

Thanks again, guys!

View attachment 612454

The pressure switch should close at 115psi nominal and open at 85psi nominal. It sounds like the switch may be a little off these settings. Regarding the system cycling, inflation's should be done with the engine at full throttle otherwise the compressor output is very low. If these these things are followed, 125psi should be plenty of pressure to operate the system.

 

[awind]

5 Lights Flashing.

I have a LMTV truck that when air pressure is up and I plug in ECU the hwy light flashes for 2 seconds then all five flash. Can you give me some directions where to start?

I see a lot of posts saying "not an expert" I am the EXPERT and I may regret joining this site but I have a desire to help people. Lets say I helped develop this product for 25 years, and may have even talked to some of you on the phone. Lets get started.
These Old systems/ECU's are not able to communicate to a diagnostic tool unless you purchase a newer ECU and connect a harness jumper with a CAN break out
Start with service manual AXTS-0015 from Dana website.
Start vehicle ECU comes up right away with 5 lights (Electrical Problem) ECU's hardly ever go bad. No lights check (Blackout)
ECU pressure checks and then faults (Pneumatic Issue) Remember the pressure switch should close at 115psi or nothing will ever happen.
Biggest Issue: Air leaks (can only be checked during inflation or the 1 second pressure check. I like to plumb shop air into the wet tank so I don't have to run the truck.(listen for leaks or snoop) if you don't have >115psi shop air disconnect the pressure switch on the tank and short the harness side with paperclip. Shop air should be higher than tires to properly run system.
Air Leaks in Seals: The air will pressurize the axle housing and exit the axle vent tubes
Second issue: Vehicle inflates to target but "deflates" after shutting off. The system is not deflating. One or more wheel valves did not close at target, when the leak back they sound like deflation. Let them leak back and check the tire pressures, you may find only one or two leaking down. Pull them apart and check for contamination. Other Issue, valves don't like extremely cold temperature, try venting the cover screw (few turns out and back in)
Won't inflate or deflate but tries: Schrader inserts may have been put back in.
Imbalanced tire pressures: Check for pinched hoses, or a clogged wheel valve
I will try and get permission to post service parts information here.

 

[70deuce]

Anyone experienced this problem. M936A2 CTIS had been working perfectly. After restart after a 60 mile and on the recovery mission of my M998 the system decided it wanted to dump all tires down to who knows what. All tires went down to about 20 PSI before I could disconnect the canon plug from the ECU to stop the deflate command. Took forever to get all back up to 80 PSI with ship's air for the drive home. The Dana manual really doesn't address uncommanded total dump. Like I said system had been working perfectly. Had used Xcountry setting and back to HWY a few times for deep snow prior to this problem and everything worked as designed. Aired back up to HWY settings fairly fast also. System comes alive as air builds up around 120PSI and immediately starts dumping all 6 tires with a steady HWY light illuminated. Selecting any of the other settings on the control panel have no effect. With ECU canon plug disconnected all tires hold pressure fine. ECU? Help!!

 

[70deuce]

Left a word out. Should have been a 60 mile drive.

 

[Suprman]

Air leak on the fill not enough to trigger a fault. System does its check and sends air to fill but a leak somewhere dilutes the air pressure so the wheel valves only see around 20psi which tricks them into dumping air. Did you hear any siren like whine sound?

 

[70deuce]

Don't remember any siren like whine. I will connect everything and check for something like that. Nice to have system but at least disabling the system allows normal use of the truck.

 

[Andyrv6av8r]

Check and make sure that all of the wheel valves are seated properly on the tubes/fittings . Check for leaks. I had the exact thing happen and had to wire the wheel valve into position until I replaced the compression seal.

 

[Jbulach]

If you have shop air to charge it with, it's a lot easier to listen for leaks without the truck running. Master switch must be on as well as start switch in the run position for the CTIS to cycle. Also hit the run-flat button to keep it trying longer and more often.

 

[70deuce]

Andyrv6av8r and Jbulach, thanks for the suggestions. I will check the wheel valves and hook it up to shop air and try the run flat selection multiple times. When attempted I will post the results.

 

[Stellaevil]

Anyone experienced this problem. M936A2 CTIS had been working perfectly. After restart after a 60 mile and on the recovery mission of my M998 the system decided it wanted to dump all tires down to who knows what. All tires went down to about 20 PSI before I could disconnect the canon plug from the ECU to stop the deflate command. Took forever to get all back up to 80 PSI with ship's air for the drive home. The Dana manual really doesn't address uncommanded total dump. Like I said system had been working perfectly. Had used Xcountry setting and back to HWY a few times for deep snow prior to this problem and everything worked as designed. Aired back up to HWY settings fairly fast also. System comes alive as air builds up around 120PSI and immediately starts dumping all 6 tires with a steady HWY light illuminated. Selecting any of the other settings on the control panel have no effect. With ECU canon plug disconnected all tires hold pressure fine. ECU? Help!!

The ECU should never start deflating without a button push to a lower setting, unless the keypad has the dreaded tin whisker...But you should see the mode light change. If the mode lite continues to flash "Highway" and the tires won't hold air, it is very cold out, or the PCU is having trouble venting and closing the wheel valves.
As you mentioned that it was snowy out, if the temperature was below 10F outside and the truck sat and cooled down the wheel valves might not be able to close at the highway pressure but they should not leak down to 20psi. After the inflate to Highway, shut the truck off and let the tires leak down. Check each one to determine if the problem is The whole truck, an axle, or 1 or more valves. If all the valves leak down the same look at the PCU vent, If just 1 axle look at a QRV vent, if just 1 valve look at the valve.

 

[Tinstar]

What aboit the ECU getting an over-voltage spike and causing problems?
The known issue with the stock alternators frying the PCB and ABS module.
Have read about it affecting the ECU also.

When my alternator went, it took out those components and my CTIS hasn't worked correctly since.
Was just airing down the front tires right after the alternator failed, now all tires go to sand and will not come up.
The air is rushing through the PCU as before when it worked.
Lights flash Hwy like normal, then burps and it flashes 5 lights. Sometimes 4
I have the DANA troubleshooting guide. Confusing at best.

Different modes hasn't helped and tried red buttons upon startup.
PCU sounds like it's working just fine, except tires are airing down.
Ive also unplugged the ECU for a reset as already mentioned with no luck.
No leaks in system that I can find and was charged with shop air.

I have a brand new Dana ECU (70psi) that I haven't installed yet.

Guess thats next unless someone has any thoughts.

 

[Jbulach]

I wonder if the transducer could be the problem, especially with 70deuce? Tinstar, the only thing I see is, all the axles feed from just one line and Tee out to the axles. So if just the front axle was airing down, you at least had a problem with a front wheel valve or dump valve.

 

[Tinstar]

I wonder if the transducer could be the problem, especially with 70deuce? Tinstar, the only thing I see is, all the axles feed from just one line and Tee out to the axles. So if just the front axle was airing down, you at least had a problem with a front wheel valve or dump valve.

Agree
but now they all do it.
The PCU is pushing air (figuratively speaking) as great as ever.

Is forcasted to be really warm this weekend. 75-80+
Will see if the cold weather has anything to do with it.

I like the system and will buy whatever I need to fix it.

The one thing I haven't done is look at the wheel valve air filters.
Cant find any for for sale either.

 

[Swamp Donkey]

The one thing I haven't done is look at the wheel valve air filters.
Cant find any for for sale either.

I have some filters. They come in a kit that has other CTIS seals and O-rings that would be helpful to have on hand.

 

[Stellaevil]

What aboit the ECU getting an over-voltage spike and causing problems?
The known issue with the stock alternators frying the PCB and ABS module.
Have read about it affecting the ECU also.

When my alternator went, it took out those components and my CTIS hasn't worked correctly since.
Was just airing down the front tires right after the alternator failed, now all tires go to sand and will not come up.
The air is rushing through the PCU as before when it worked.
Lights flash Hwy like normal, then burps and it flashes 5 lights. Sometimes 4
I have the DANA troubleshooting guide. Confusing at best.

Different modes hasn't helped and tried red buttons upon startup.
PCU sounds like it's working just fine, except tires are airing down.
Ive also unplugged the ECU for a reset as already mentioned with no luck.
No leaks in system that I can find and was charged with shop air.
I have a brand new Dana ECU (70psi) that I haven't installed yet.
Guess thats next unless someone has any thoughts.

If the ECU was damaged by a voltage spike it would be randomly flashing or dead. When the ECU comes up flashing "Highway" it is working fine, if there were an electrical problem it would 5lt fault immediately. If it flashes until the pressure check then 5lt fault, it is a pneumatic issue (large air leak maybe). If the pressure switch is shorted closed the system will try to inflate with too low supply pressure and the tires will start dumping air. The system should not start working until the switch closes at 115psi and stop working when it opens at 85psi. This could account for the occasional 5lt fault if the supply is less than 10psi and the system tries to check the tires because it sees the switch closed.

 

[Tinstar]

I have some filters. They come in a kit that has other CTIS seals and O-rings that would be helpful to have on hand.

PM sent

 

[Tinstar]

If the ECU was damaged by a voltage spike it would be randomly flashing or dead. When the ECU comes up flashing "Highway" it is working fine, if there were an electrical problem it would 5lt fault immediately. If it flashes until the pressure check then 5lt fault, it is a pneumatic issue (large air leak maybe). If the pressure switch is shorted closed the system will try to inflate with too low supply pressure and the tires will start dumping air. The system should not start working until the switch closes at 115psi and stop working when it opens at 85psi. This could account for the occasional 5lt fault if the supply is less than 10psi and the system tries to check the tires because it sees the switch closed.

The kicker is there is no pattern per sey.
Different each time.

The pressure switch is the one on the PCU correct?

Edit;
I will look in the TM