CTIS issue and questions

[Ssmax]

Hey guys I'm Dave.

I recently picked up an m936a2. I'm having an issue with the CTIS ( big surprise) I've searched this site quite a bit and I've read the dana eaton troubleshooting guide. But I still haven't found anything addressing the problem I have.

The issue is I start the truck, the highway light is flashing I get to 125psi it's still flashing. The pcu is not clicking or anything. I can drive around for 30-40 mins and it's still just flashing. If I select any other modes they flash but no dumping of air no pcu clicking. Nothing. But it's only one blinking light. Has anyone ever had this issue?.

 

[Reworked LMTV]

Along those same lines, is are the electronics in the box SMS or discrete? Can toasted parts be accessed or are they dipped in a plastic,etc?

 

[therooster2001]

HI Dave, congrats on the big truck. As far as the CTIS, the air pressure seems a bit high, but still tolerable, you might check the governor it might be a bit high. The unit will flash in a mode, then after it reached pressure it will go solid. It's not normal for it to go 20-25 min, nor no noise from the pcu. What are the tire pressures at to start? Do you hear any of them filling or any leaks? If nothing at all, it could be the pressure switch by the wet tank is not working, but that should cause the five flashing lights. Do you have a spare ECU to test with? Have you double checked that all the connections to the PCU are there? air and electrical?

 

[Andyrv6av8r]

I'd turn your governor up a bit like Rooster said. Your gauge may be off a little and the pressure isn't high enough. Can you put shop air on it?

 

[Ssmax]

Thanks for the reply guys, so the air pressure to start in the tires are 80psi I aired em up manually, I checked the air connections at the pcu, no leaks there. I have the yellow line and black air line going to it, Both the cannon plug on the side and 3 pin connector are fully connected. I don't hear any filling or anything. It's like the whole system is dead. I didn't have enough time to check the governor yet, I'll do that later today ( we got quite a bit of snow yesterday).I'm leaning more toward a potential bad ECU? Could someone have hooked up the airlines wrong to the pcu? ( I know it's a streach).

 

[Coffey1]

Ecu failure is all lights on solid no flashing.

 

[therooster2001]

Hooked up wrong is possible, we've seen a lot of bad stuff on rebuilds, or mud wasps blocking up vents that made a condition the TM won't cover. it's an in from the supply and out to the wheel valves, really simple. Since the truck is new to you, we need to check and know basics of the truck. There's a lot of pieces to CTIS, so we'll go through them, but we'll get it! Do you have a Dana or an Eaton ECU? The Dana / Spicer allows the wrecker to get to 80, but the Eaton is 70 if I remember right. I want to see that ECU give you anything but flashing that long. Have you put it in run flat? That should ignore all leaks and then return after 10 min. I'd like to see it switch modes on its own to verify its good. Usually when it goes, it will not power on, or go all solid as Coffey noted. When truck builds up to 85psi, that pressure sensor will trigger the system to work, that's when the CTIS will engage the PCU. Are your pressure gauges working?

I think we might need to go REALLY methodical. WP 149 in the Field Maintenance TM has a good procedure to check electrical connections and air of the systems. Take a read if you haven't and at least go through that procedure to rule out a couple of more things. Let us know what you find.

Edit: and because you have a wrecker, we might need to see if you have the upgraded parts to get to 90psi, so post some pics of the ECU labels, and the PCU. I have a feeling it's the older one.

Did you get the truck from auction or a personal sale?

 

[Jbulach]

I wonder it may have the new 90psi ECU but not the new transducer that is supposed to go with it, or vise versa?

 

[Ssmax]

OK so I think we might be getting somewhere, I tried the run flat setting while being in highway and about 3 mins after the truck hit psi the valve clicked and started bringing secondary pressure down... would that mean it's filling the tire to highway? Ignoring the leaks?. I'll post pics that you asked for as soon as I get out of the cab of the truck lol.

 

[Ssmax]

This is when the truck was in the runflat/ Highway mode. secondary looking like its filling tires. this is after i heard the pcu clicking





Here are the other pictures you requested.


I will say that after the truck went through a few fill/ dump cycles the run flat light turned off from blinking and highway light stayed on solid. after a few mins the light went to blinking and the truck began to fill the tires again

So am i right in assuming I could have a leak somewhere in the system that its trying to compensate for? Thanks for all the help guys. I'm definitely learning a lot. I also bought the truck private sale but he didn't really mess with the CTIS he said.

 

[WYomer]

You wont like 80PSI unless youre loaded down. I drove 68psi and it was too much.

Check for override valves between the tire and CTIS wheel valve. Mine blinked when I was at 68 PSI 5 lights and my first fix was taking those out and airing down/up to around 55psi. ran great about 2 months until the next CTIS issue popped up.

 

[Ssmax]

I've manually aired up the tires to 80 when I first got the truck. Rode great, the wrecker is a heavy girl as it is. I had a 923 I kept it at 55, and that was great. Yeah I'm starting to see it can be a really finicky system. Since my last post though I've successfully cycled from highway to cross country. Then back to highway and have had the valve click and light stay solid. Once in highway it will cycle from solid to blinking then fill up and dump air for a second. I assume that's normal

 

[Jbulach]

Yep, you want at least 80 psi in a wrecker.
Look on the bottom of your ECU, that is where the sticker should be with all your information on it, see if you can get a picture of that. Also check the transducer to see if there is any information on it, or a tag on the wire pigtail coming off of it.

 

[Jbulach]

It sounds like you may be functioning somewhat normal, maybe just a leak. Also, run flat mode does help the system ignore leaks. Now is where you would want to get it on shop air if possible and use your ears to try to find a leak.

 

[Jbulach]

....Check for override valves between the tire and CTIS wheel valve. Mine blinked when I was at 68 PSI 5 lights and my first fix was taking those out and airing down/up to around 55psi. ran great about 2 months until the next CTIS issue popped up.

What are theses over ride valves you speak of? Any pictures?

 

[Jbulach]

It sounds like you may be functioning somewhat normal, maybe just a leak. Also, run flat mode does help the system ignore leaks. Now is where you would want to get it on shop air if possible and use your ears to try to find a leak.

With the truck off, air up to 120psi, turn master switch on, then turn the start switch just to the run position(do not actualy start the truck), hit highway mode and the run flat button, get out and check for leaks.

 

[Ssmax]

Awesome I'm going to get on that probably tomorrow. I'll also get those pictures you wanted of the ECU when I get out of work. FWIW before I left for work the truck cycled from sand to cross country, to highway twice with the light coming on solid for each setting. Also it wasn't in run flat mode. I do however hear a leak coming from the left tire area on the final axle. Thanks for the ideas so far! Definitely didn't think I'd actually get it somewhat working!

 

[Coffey1]

Just some more important information don't take power cable off euc and put back on with truck powered up could possibly spike the euc.

 

[therooster2001]

Its alive! That ECU looks like an Eaton, double check the tire pressure when it's solid to verify what levels they are set at. Wreckers are special, and those ECU's have the capabilities of being jumpered (in the manual, but I haven't found them) so it would be good to know YOUR pressures at the various modes. Test it before you need it. Good to hear that it cycles more normally. Run down the leaks and I bet it's golden. I don't like to see it dump the secondary that much, probably another indication of the leak. I have a feeling you'll have more to dig in on the truck. Keep us posted on the CTIS and the rest.

Glad she's breathing.

 

[Ssmax]

Yeah its an Eaton, I wasn't able to get a picture of it for you guys but I saw the sticker on the back where it said Eaton. I was able to get a reading of tire pressure in highway mode and all the tires were between 78-80psi. I'll get the other readings when my neighbors are up so I won't wake em with an air dump haha. I looked into the wrecker having updated parts to achieve the 90psi. I was able to find all the part numbers for the wheel valves and the transducer that goes into the PCU I also found an ECU direct from Dana that is required for 90psi However the price I found it for was brand new at 2800$. I have all the older parts on my truck. But it works. As soon as the snow melts a bit then I can crawl around and start pin pointing leaks. Again Thanks everyone for all the help.

Here is some documentation I found. Hope someone can use it