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ElizabethMeyer

2500 Allison and no full throttle downshift - at times

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On 12/9/2018 at 7:42 AM, DickandLois said:

The Lack of DCT's ( Diagnostic Trouble Codes) Will drive tech's nuts.

Rich, that in of itself leads me to believe its either a TCM or a wiring (ground with excessive resistance) malfunction(TCM= Transmission Control Module) reason I say that, on an Allison the moment a down shift is commanded and it doesn't happen it will log a fault code. Modules in general when they have an internal problem they will NEVER admit fault. Cycling the key could reset the module internally or for that key cycle could present less resistance in the ground circuit due to something else not drawing on a particular ground circuit. Being a Freightliner chassis presents another level of concern; notorious wiring problems, they lead the industry with poor routing, undersized harnesses and inadequate grounds. This could take a GOOD technician several days to figure it out, or a technician that has a test module laying around to swap it in and take it for several rides.

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Thanks for you'r reply Joe. That is one reason I ask if the internal hydraulic pressure has been measured.  Having that info could reveal an issue with a internal pressure switch not responding. 

The other item(s) you mentioned. Poor ground point(s) are always on top of list when it comes to intermittent issues.

Asked Mark if this issue has been more prevalent over time. From seldom to almost every startup cycle. 

Marry Christmas and Happy New Year !

Rich.

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Well, a little update albeit without much data. Went down to the dealer Wednesday and drove around with the interactive device plugged in and sending real time data to the Level 3 tech. He had them replace the manifold pressure sensor (I think?) and we repeated the tests in both modes  "Working" (Power) and "Not Working" (Derate) with no change. Now the Level 3 tech is coming to the dealer on Tuesday just to see me. I am now the guy you never want to be. The guy who has a problem that is stumping everyone. Yay!

This will be the third time I will  be going down. A couple of good things. One, I have been able to arrive with it in "Not working (Derate)" mode both times. The first time it took me running around the neighborhood like an idiot and cycling the key 30 times before I could get it into "Not working (Derate)" mode. (Stop, neutral, key off, key on, drive, hit 26 mph,  downshift working - CRAP, repeat 30 times till it WON'T downshift.) Wednesday it started out in "Not working (Derate)" mode. I was also able to get it from Derate to Power mode and back to Derate mode after 6 or seven tries for each flip down at the dealer. It does appear that everybody is leaning towards the engine as the culprit for not making power when it should but nobody has identified the cause yet. It also seems that warranty will cover at least the parts and I'm hoping the labor because I'm burning a fair amount of tech time. Now we have 4 new parts: ECM, TCM, TPS and the pressure sensor.

I am providing them with the info from you guys but I'm not sure it is registering. 

Mark

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23 minutes ago, ElizabethMeyer said:

I am providing them with the info from you guys but I'm not sure it is registering. 

Mark, From the information, including the replaced parts. It looks more and more like an electrical issue. Intermittent connections can drive the best techs nuts. 

By replacing the modules - That kind of confirms the issue is, corrupted data or communications,  Not the Modules When the system works / it works fine and when it goes south it is in that state for a number of key cycles at times. How many miles on the Coach? Think I remember it's like 3 years old. 

Have you or do you park where rodents are around? Also, there is a good possibility of an unseen location  where the wiring is pinched or rubbing some where. 

The CAN Data string is a blur in real time because of the system clock speed, But any bad packets should trigger an error code. The fact that there are none, Leads one to look at the dumbest circuits .

Your coach slipped through with a hidden snake in the grass and they do not come with redundant systems.

Rich.

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Coach has 15K and I've put on 10K of that. If the problem is mousies, they got it before I purchased it because this problem has always been there for me.

Loves to eat them mousies, mousies what I loves to eat, bite they little heads off, nibbles on they little feets. (B. Kliban - 1975)

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Here is a another update. Cummins Level 3 was supposed to meet me at the Cummins dealer on Tuesday but the stupid coach would not flip into "not working/derate" mode. Drove around my neighborhood for almost two hours, stopping, starting, driving, stopping, starting, driving. Must have cycled that thing 60 times and couldn't get it to flip. Called the dealer and let him know that I would continue to try. The Level 3 guy was already there. About 5 minutes later I got a call from the guy and he said he wanted to change plans. Instead of having me come down he was going to requisition a recording device to capture what was happening and he would call me and come to my house to install as soon as he got hold of one. Even more importantly he was already in discussion with their Systems Integration team, the guys who work directly with the other vendors to make all this stuff work together. They are going to work with him to find out who is not sending or receiving the signals properly and get the vendors' systems working together and keep me out of the finger pointing that has been going on for over a year. In other words, own the problem. HALLELUJAH. Haven't heard back yet but I'll be following up on the 26th if I haven't heard by then. Betsy and I are leaving for a month long trip to Texas so I'll have plenty of opportunity to demonstrate the "not working/derate" mode to his new recording gadget.

I did ask him why the first gadget didn't capture what he needed and he responded that it had some glitches and the Systems Integration team also wanted something different than what the first device was capable of.  

 

Stay tuned!

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I have a 2014 Berkshire with the 340 and same transmission.  I have had the exact same issue in the year since we purchased.  I came across a thread somewhere and for the life of me cannot recall where I found it.  However, it stated that the turbo boost will not react well if the engine has idled at low rpm's for any time.  They suggested to high idle at 1200 rpm if idling more than 5 minutes.  Since following this process it has had a noticeable effect although we have still had occasions of needing to manually downshift on the hills.  There are three idle modes.  Normal, medium(950 rpm) and high(1200 rpm).  On my unit, high is achieved by pressing the cruise control set speed button.  Medium idle is set by pressing the resume button.

I have not been able to find further documentation on this and it may have been on a trucker forum.  So far is has been working.  I know there are many discussion on pros and cons of high idle but for me this has been working.  If anyone has more on this or the high idle and turbo boost please let us know.

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Hi,

This is Mark, the OP. Thought I would give a quick progress update. It may help people with an Allison 2500 who are experiencing no downshifts even at full throttle. I've worked with two different teams of Allison and Cummins techs over the last 6 months. That is in addition to the original time and money spent at Allison and Cummins trying to get this thing diagnosed. The first team worked with me down at Tiffin in Red Bay. That ended up with no fix and Cummins and Allison nicely pointing fingers at the other and Bob Tiffin pointing me to Freightliner. By this point the ECM, TCM and TPS had all been replaced without fixing the problem. The coach still would randomly not downshift at full throttle under conditions I knew it should and could. I had demonstrated that to the techs over several days.

I had just about given up when I called Cummins about warranty coverage and got a tech person who was genuinely interested in my problem. That got be kicked up to Level 3 and I got a tech that was EXTREMELY tenacious. He ended up arranging a meeting with me, himself and an Allison tech for two days down at a local Cummins shop. Best two days ever with both guys taking turns plugging in their PCs and discussing possible theories as they were gathering and diagnosing data and findings.

The end result is that it looks like it is a software bug on Allison's side. Not confirmed yet but data is pointing that way because they are seeing this problem elsewhere on other vehicles. It is is tied to, and triggered by, cycling the key on and off. The thought is If you cycle the key off and then on too quickly, the software pulls the wrong value for the "road speed limit" parameter and that in turn causes the transmission to not downshift at full throttle. 

I am just starting to test this theory by cycling the key from off to on and then waiting 10 seconds before starting the vehicle. This slow cycle supposedly allows the data to fully load into the TCM. Quicker cycles cause that load to get interrupted somehow.   I should finish my testing this week. Today it worked correctly 10 times in a row but my experience is that those results are not definitive. My data to date says that anytime I leave the RV sitting over night I have about a 50% chance of it being in "working" mode versus "not working" mode" the next day. So until I get a few more days of those data points I won't really be comfortable saying this slow cycle works. Allison says that they are doing the slow cycle on a fleet of garbage trucks and it has worked 100% of the time.

Just to refresh what my problem is. I know my trans shift  points at full throttle by heart now on flat roads in good conditions. It will downshift at 25, 35, and 45 (other points too but these are the three I use as test points) at full throttle every time when it is in "working" mode. When it flips over to "not working" mode after a key cycle, it will NOT downshift at those same points. It just slowly accelerates. 

I'll keep everybody posted on the rest of my testing this week.

Mark 

  

 

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Mark, Thanks for the update. Glad to hear that they are working with you on this nasty bug. 

       By this point the ECM, TCM and TPS had all been replaced without fixing the problem. This exchange of parts should have solved the issue if it was a software issue , from my point of view.

Pointing to being to fast on the ignition switch is iffy.  Maybe changing out the darn switch if they are leaning that direction.  Got this gut feeling that when the bug is located it is going to take some thinking out of the box  and a stupid / basic fundamental item. There are a number of them between the key switch and the start up sequence.  One simply bad crimp, a wire in the harness that is picking up a random noise pulse between 2 wires in the primary startup sequence, that should not and is not present in the thousands of other chassis or a device that when energized at the ignition on sequence creates a noise spike induced into the data startup sequence. 

Going to take a few more cold ones or glasses of wine. LOL

Worked for years in the electronics field and a few nightmare issues. The level of electronic systems has expanded exponentially.  

Rich.

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Mark, Kind of like a dog with a good bone, so the gray matter is just chowing on this.

This is the information you sent to Carl earlier.

          Both the Cummins tech and the Allison tech have plugged in. Multiple times.  Cummins shows 100% response to TPS full throttle request in "working" and "not working" modes. Allison shows 100% in "working mode but only a partial throttle request in "not working" mode. What the Allison computers shows in "not working" mode is what I term a rolling throttle response. Meaning, that when I have the pedal to the floor, instead of seeing 100%, Allison sees a request for 40% that then rolls up to 90% or even 100%. It doesn't always hit 100% often pegging around 94% throttle request. 

          This is looking like a system Prognostics issue.

 

Allison Prognostics Generation 5 Transmissions

                For the 3000 and 4000 series trans missions. No listing of the 2500 series transmission.

You Coach was built in, or is listed as a 2015 model year with 2500 series that is a generation 4, 2500 transmission.

Allison Prognostics Generation 4 Transmissions

                 Shift Selector Models Detailed information on oil levels, diagnostic codes and prognostic features for your specific shift selector can be found on the following pages. If your vehicle has a shift selector that has a: - Double-digit display and was release after July 2008, equipped with Model Year ’09 prognostics, see the section for Model Year ’09 4th Generation Electronic Controls Shift Selectors. - Double-digit display and was released after July 2008, not equipped with prognostics, see the section for 4th Generation Electronic Controls Shift Selectors. - Double-digit display and was released prior to July 2008, see the section for 4th Generation Electronic Controls Shift Selectors. Check the link listed below

                General Information FLUID LEVELS

    The transmission fluid cools, lubricates and transmits hydraulic power, so it is important the proper fluid level be maintained at all times. If the fluid level is too low, the converter and clutches do not receive an adequate supply of fluids. If the fluid level is too high, the fluid can aerate causing the transmission to shift erratically or overheat. If the fluid level sensor is reading a low level, that would restrict the shift issue you are facing IMHO. 

DIAGNOSTICS The Transmission Control Module (TCM) of your Allison Automatic monitors the transmission’s electronic controls; and when a problem condition is detected, it: – Restricts shifting – Illuminates the CHECK TRANS* light on the instrument panel – Registers a diagnostic code Continued illumination of the CHECK TRANS light during vehicle operation (other than start-up) indicates that the TCM has signaled a diagnostic code. * For some problems, diagnostic codes may be registered without the TCM activating the CHECK TRANS light. Your Allison Transmission authorized service outlet should be consulted whenever there is a transmission-related concern. They have the equipment to check for diagnostic codes and to correct problems.

                 http://www.rtsallison.com/downloads/4th_gen.pdf

One item I can not look into is if there is by chance a difference between the 2009 and the 2015 shift selector system ? That does not like the the 4th. gen prognostic software used.

Kind of reaching for straws at this time.

Rich.

Late night internet works well after the Camp Ground load drops.

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Day two:  slow key cycle worked again. 10 cycles of off, on, wait 10 seconds, start, drive, try a couple of full throttle downshifts at known shift points. Repeat.  

 

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1 hour ago, ElizabethMeyer said:

Day two:  slow key cycle worked again. 10 cycles of off, on, wait 10 seconds, start, drive, try a couple of full throttle downshifts at known shift points. Repeat.  

 

Kind of good News!  Might indicate that a faster retry of the ignition on / restart cycle does not allow time for the Prognostic data to be dumped and the old and new data load at startup corrupts things. The gen 4 prognostic information does mention circuit # 135 ground circuit and that could be an issue.

Thanks for the feedback. Rich.

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Day 3 tests all positive. Tomorrow, Day 4, will be statistically significant because it has never stayed in "working" mode 4 days in a row since I have been aware of the problem and starting tracking it.  I'll post Day four and then wait to post until I have finished the rest of this week's daily tests until I finish Day 10.  

 

 

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On 12/9/2018 at 10:19 PM, RayIN said:

Start with the lowest cost items to replace, I would replace the ignition switch before diving into expensive diagnostic tests.  I know I need to replace mine(I can remove the key in any position), once a year the gauges will swing from operational to pegged to the max., and the engine stops for perhaps 1 second the resumes running. I pull over, turn of the key and wait a minute, restart the engine and everything is normal again for many months.

Hello Mark. That was an unrelated reply I made, sorry.

I just reread every reply and your detailed explanations.  **** and Lois touched on wiring. In a completely different situation with my old '02 Chevy dually,  my mechanic finally found a broken wire in undamaged covering that was in a wrapped bundle. It would not make contact sometimes, but if the harness moved a bit it made some contact again.

I don't know if this may be connected to your problem, I'm just throwing it out there for speculation.

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Day 4 and all remains good. 4 days and 40 key cycles. I'll report back when I finish the 10 days but the slow key cycle work around is looking good.

 

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