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Old 05-31-2018, 03:44 PM   #1
Mini-Skoolie
 
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Allison 2000 Gremlins - Help Request

Hi All,

On my maiden voyage, bringing Dora (our new Skoolie) home, I ran into a weird issue that 2 shops had issues re-producing. I'm hoping someone has run into this issue before and might have some insight into what may be root cause.

Bus Specs:

BlueBird TC2000 2001 78 Passenger Bus
Cummins 5.9 Power Unit
Allison 2500 5 speed transmission
133,100 Miles actual on the unit

Here's the deal :

Left school yard, running down I-65s, running smoothly at 2100 RPMs and 70mph. The maintenance manager at the school opinioned that he wasn't sure that the fuel gauge was accurate and that I may want to top off fuel. I pulled off and filled up, fired back up, and as I was merging back onto the freeway, I got a "Transmission Fault" light.

The bus had shifted from 1st to 2nd, 2nd to 3rd, and then did a soft lurch like it wanted to go into 4th, but then fell back and stayed locked in 3rd.

I tried completing shutting down and starting the bus back up. This cleared the check trans light, however, once I then put the transmission in gear, when I hit 3rd gear, the bus once again locked down into 3rd and refused to downshift or upshift from 3rd.

I was able to limp to a truck repair shop, where the mechanic on duty worked with me to disconnect the bus battery negative terminal an effort to force a reset and re-learn of the TCM. As you can guess, this cleared the check trans light again, but had the same issue.

At this point, the mechanic at the first shop (very nice guy) suggested I limp 10 miles down the road to Rocket City where there's a Cummins/Allison shop. I managed to make it there and had diagnostics run while the unit was in fault - made it there driving 30mph on I-65s which was a load of fun....

Codes we pulled :

P0562 - System Voltage Low
P0732 - Incorrect 2nd Gear Ratio (shop said this was when it couldn't downshift into 2nd)
P0734 - Incorrect 4th Gear Ratio (shop said this was when it couldn't upshift into 4th)
P0847 - Transmission Pressure Switch Solenoid D Circuit Stuck Closed
P1711 - Transmission Pressure Switch Solenoid E Circuit Stuck Closed
P1721 - Solenoid B Controlled Clutch Not Engaged
P0708 - Transmission Range Sensor Circuit High Input

Codes were pulled via latest Allison software for Allison 1000/2000 Transmission software. They reset and cleared the codes, then performed a road test with me driving. They had me drive the unit pretty aggressively, up hills (to stress and heat the transmission), start and stop traffic, freeway, etc. Very thorough, lasting for about an hour.

We were unable to reproduce or cause the Check Transmission condition. The shop owner whom went with me was live data logging and didn't capture any new codes.

The only item we found actionable was that the transmission had 3 qts of tranny fluid over the "hot high" marker, so they drained it down to max high line while it was hot, and then re-checked once the tranny cooled down.

The shop spent nearly 6 hours working on, testing, etc. and really worked with me, while only actually charging me for 1 hour labor, diagnostics, and the fluid drain labor - I felt the bill was quite reasonable given the amount of over the top time they spent trying to force the same error to re-occur.

The shop manager opinioned that since we couldn't re-produce an error after clearing the codes that either because the bus sat for 2 months and then got run fairly hard (by me) down the highway that a solenoid or two had stuck but had worked themselves free. He also opinioned that he had occasionally seen where bad codes could cause the bus to enter the limp home mode it was in when I arrived - and that by clearing the codes, this could also be the root cause for the issue, and why it now runs as if nothing ever happened.

All of that background I wanted to share to see if anyone had any similar experiences with their Skoolies that have Allison trannies. I have to head 3 hours back over tomorrow to try and make it the rest of the way home - I'd be lying if I said I wasn't nervous after all of what happened.

Does anyone have any ideas, thoughts, comments ? Does it make sense for bad codes to cause the issues and clearing codes making them go away ? Sitting for 2 months causing solenoids to stick ? I'm a computer guy, so logic is my friend, but in this case logic isn't making sense to me.

I'm all ears

/Matt
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Old 05-31-2018, 04:35 PM   #2
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At least you're an expert on that issue now. Piece of mind knowing Alison has gone through your tranny.
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Old 05-31-2018, 04:52 PM   #3
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This is very much a shot in the dark.

I have seen low voltage issues caused by a bad ground cause all sorts of random codes in an auto ECM. Codes that were all over the place.

Corrected the ground connection on the ECM and the troubles went away.

Hopefully Christopher will chime in. He is a true Allison Geek.
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Old 05-31-2018, 08:26 PM   #4
Mini-Skoolie
 
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Quote:
Originally Posted by o1marc View Post
At least you're an expert on that issue now. Piece of mind knowing Alison has gone through your tranny.
Hah, I'm far too humble to think I'm anywhere near an expert LOL. It does feel good that they went through it, but feels bad that we couldn't make it re-trigger. I'm that IT guy that wants to know WHY a server or application broke, even when it auto-fixes, and I'm known to go through dozens of shovels digging for root cause. I'll be grateful if it makes it home alive tomorrow, but will be thinking the entire time what caused it to trigger until I know.
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Old 05-31-2018, 08:29 PM   #5
Mini-Skoolie
 
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Quote:
Originally Posted by PNW_Steve View Post
This is very much a shot in the dark.

I have seen low voltage issues caused by a bad ground cause all sorts of random codes in an auto ECM. Codes that were all over the place.

Corrected the ground connection on the ECM and the troubles went away.

Hopefully Christopher will chime in. He is a true Allison Geek.
Hey ! Yeah, the low voltage flag had me wondering the same. I'm going to look at and request the shop look at that too before I pull off in it (The voltage @ the alternator).

I did more digging today - google-fu says an alternator going bad is a common root cause, since the TCM is pulling power from there (supposedly - I haven't validated that's the case specifically for this bus, but saw other buses were wired with Allison 2000PTS and 1000PTS trannies this way. Mine is apparently a 2500PTS).

I'd love to here from Christopher - I'm here to learn, my name is grasshopper...
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Old 05-31-2018, 08:37 PM   #6
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Low voltage will make your allision go BONKERS... you likely never made it to 3rd.. it likely went 1-2-Lock (which feels like 3rd).. and went into Limp mode. which is real sluggish on takeoff and the shifting you experienced..



if the harness connector on the trans ever got water in it on the large "round" connector. you'll get these gremlins too.. stuck solenoids are often a result of low voltages.. your grounds and power wires to the TCM are ALL-important..



the incorrect ratio codes are caused by the solenoids failing to operate and shift the transmission.. the TCM commanded-gear and TCM actual gear will mismatch and throw an incorrect gear error.. I would go out and buy a litle digital dashboard volt meter and first measure the voltage on your electrical system as a whole as you drive.. when you hit bumps does the voltage bounce? is it in the 13-14 volt range?


if thats good then you wire it to the BAT pin of the TCM.. (the TCM ignition pin isnt where it gets it main power)... if that voltage doesnt match system voltage then you have a ground or supply wire issue..



-Christopher
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Old 05-31-2018, 10:49 PM   #7
Mini-Skoolie
 
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Thanks Christopher - that's super valuable. I'll see if I can get the shop to wire me up meters before I leave. I saw your note about watching system voltage - there's already a default voltage meter on the bus that I didn't pay attention to previously (but I guarantee you I will now). I'll see if I can get a meter put on the batt pin so that I can monitor both on the drive home.

Either way, I'll report back tomorrow with what I find. If you have any other thoughts (or anyone else for that matter), I'd love to hear them.

I feel slightly encouraged that the shop did state the overall mechanical overview of the bus is positive, evidence that the engine was well maintained as was the tranny from the way it acted and drove.

/Matt
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Old 06-02-2018, 10:10 AM   #8
Mini-Skoolie
 
Join Date: Jun 2017
Location: Woodstock, GA
Posts: 25
Year: 2001
Coachwork: Bluebird
Chassis: TC2000
Engine: Cummins 5.9 L6
Rated Cap: 78
Just to update -

Made it home, about 175 miles, with a bit of mountain driving coming in and out of Chattanooga on my way to Dora's new (temporary) home while we re-fit her in Calhoun.

No issues what so ever, my only complaint is really a project I need to research - how to add a retarder or jake brake. I'm sure it's been done, I just need to break out google-fu skills.

Thanks for all the suggestions above. I will be going back over the bus again thoroughly - the voltage stayed rock solid the entire way home on both alternator and the batt feed on the TCM.

/Matt
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Old 06-02-2018, 10:13 AM   #9
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Quote:
Originally Posted by atl_oldskool View Post
Just to update -

Made it home, about 175 miles, with a bit of mountain driving coming in and out of Chattanooga on my way to Dora's new (temporary) home while we re-fit her in Calhoun.

No issues what so ever, my only complaint is really a project I need to research - how to add a retarder or jake brake. I'm sure it's been done, I just need to break out google-fu skills.

Thanks for all the suggestions above. I will be going back over the bus again thoroughly - the voltage stayed rock solid the entire way home on both alternator and the batt feed on the TCM.

/Matt
A jake would be very expensive and complex.
A retarder would be simpler since they actually can be found on SOME western school buses out in the Rockies. But its gonna be pricey to add one.
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