CTIS Pneumatic Controller Question

[DeuceRoadTripper]

re: CTIS Pneumatic Controller Question

Have an M923A2 with CTIS unit. System has been working fine for two years with no air leaks. One day I dropped the air pressure on the ECU to cross-country mode. The system aired down fine. When I went back to highway mode the pneumatic controller attempted to fill once then faulted out (5 flashing) lights. Each time I attempt to reset or change to any mode on the ECU – the pneumatic controller discharges a single short blast of air from manifold vent port and then the EUC faults out (5 flashing) lights.

I cleaned and checked all pins to the ECU, pneumatic controller and verified the pressure switch operational. I bleed out all the air from the system by dumping the tanks to zero. Then restarted the engine to allow pressure to come up to 120 PSI - during this time, the ECU flashed highway only (which is normal and correct) until the pressure switch determined 120 PSI is available. The pneumatic controller then discharged a single short blast of air from the side vent port on the pneumatic controller manifold and the ECU faults to (5 flashing) lights.

I suspect the pneumatic controller has failed.

Just wondering if anyone has had this particular problem?

 

[98G]

I doubt it's the controller. If they fail they go to 5 solid lights.

Maybe Alexsha will chime in with more knowledge. ...

 

[DeuceRoadTripper]

Here’s a bit of extra information – this whole problem started shortly after leaving a car show where the vehicle was on display. During the day I had to hood up for the kids to see. Of course I noticed a couple of men standing next to engine on the driver side. One of these geniuses was between the hood and the front tire with his hand behind the rubber fender. When I asked them if I could answer any questions, they walked away. I couldn’t help thinking they were up to no good?

I have been all over the front left side of the engine. There are no cut hoses or pulled electrical. The only thing that might affect the CTIS system in that area is the quick release valve at the front. I have plenty of pressure, no leaks; all valves that should be closed are closed; all valves that should be open are open. It was just a strange coincidence…

 

[Andyrv6av8r]

I am having the exact same issue. My CTIS has always worked flawlessly. Yesterday I aired up the truck with shop air thru the front gladhand. It hit 120, checked pressure and aired up a normally slightly low tire just like it always had in the past. I decided to air down to SAND then back up. SAND light on the ECU blinked with no response from the air controller (PCU). I aired it down and powered the truck down ( all electrical off), disconnected the ECU cannon plug. Started over. I actually did this a couple of times with no change. The final time at 120, it released a loud blast from the threaded hole in the PCU ( which is just a vent)and simultaneously dumped air from one or all of the dump valves and all 5 lights flashed. Now the odd part to my story is it worked perfectly until I switched over to a Delco 70amp SI21 alternator two days ago. Go figure?

 

[Coffey1]

When things decide to fail is out of our control.
My batteries were working perfectly. Then on the next start up poof. I would not read much into the two things men and new alternator. Crap just happens at the wrong time.

 

[Monkeyboyarmy]

I would guess that the pressure switch on top of the pcu has failed. I know they are voltage sensitive.

 

[Alexsha]

If your PCU is clicking and air is moving at all, then it's unlikely to be an issue there. It seems more likely to be the pressure transducer on top of the PCU or an air leak or obstruction. If something is clogging an air line the CTIS will shut down.

 

[todds112]

I replaced the pressure transducer on mine with a NOS one. I also fixed my PCU after screwing up the reassemble (switched solenoid locations). My CTIS works fine now, but it does still chatter on refill. System works fine, airs down and back up like it should.

 

[DeuceRoadTripper]

Off hand, does anyone remember what size the compression fittings are on PCU?

 

[WSm925a2]

Where did you find the NOS pressure transducer, and where is a good place to purchase ctis parts in general for a 1991 m925a2?

 

[Suprman]

Check your rear wheel valves. They are on a stem coming out of the hub with a compression fitting and have a bad habit of slipping up creating an air leak, but still visually appear to be in place.

 

[awind]

I bought one from the link attached. Don't be in a hurry. Comes from China. Go figure. Part worked great though. Good Luck. http://www.aliexpress.com/item/Pres...itch-16412-676505-16412676505/1579141630.html

 

[74M35A2]

Reboot the system. Once you have 120 tank pressure, shut the truck off and back on. Then press the two lower red buttons. After 30 seconds, then press the HWY button.

 

[bikeracer917]

Hi all. I've been reading your posts and comments.... I have a m1078a1 with 24 volt ctis. I have 5 lights on steady. From what I read it's possibly the controller. Or even an electrical issue in the pnumatic control unit. Do any of you have any knowledge about the possible causes?

 

[Suprman]

Check the contacts at the pneumatic valve in the passenger kick. Check the pressure switch on the air tank. Make sure you have air at the pneumatic valve. Visually check everything. Other than that the easiest troubleshooting is to swap the controller with a known good one.

 

[awind]

In my case I had to bump up the pressure on the air regulator. The switch on the air tanks was not closing.

 

[jamestiede]

CTIS problem

Here’s a bit of extra information – this whole problem started shortly after leaving a car show where the vehicle was on display. During the day I had to hood up for the kids to see. Of course I noticed a couple of men standing next to engine on the driver side. One of these geniuses was between the hood and the front tire with his hand behind the rubber fender. When I asked them if I could answer any questions, they walked away. I couldn’t help thinking they were up to no good?

I have been all over the front left side of the engine. There are no cut hoses or pulled electrical. The only thing that might affect the CTIS system in that area is the quick release valve at the front. I have plenty of pressure, no leaks; all valves that should be closed are closed; all valves that should be open are open. It was just a strange coincidence…

I had the very same thing happen to me after alternator install. One thing I did notice was that the voltage is only one half volt lower than OEM voltage.
Now I have air leaking from both of my axle vents while its trying to inflate.