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Old 04-08-2021, 08:23 AM   #1
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Join Date: Apr 2021
Location: Columbia, SC
Posts: 8
Year: 2003
Chassis: International 3800
Engine: DT466E w/ Allison 2000
Allison 2000 TCM Failure - Need Advice

Hey all,

Long post, and I apologize. Fingers crossed CadillacKid chimes in.

First time poster here after lurking a bit. My family and I recently purchased a 2003 International 3800 72 passenger bus with a DT466E and Allison 2000 transmission. 128k miles. Drove to Alabama with my daughter and brought it back to South Carolina with no issues. The bus ran great.

The bus has been in between storage and the house to do minor things (remove seats, decals, etc.). One day the check trans light came on and the bus wouldnít go past 15 MPH (approximately 2600 RPMs). Pulled over, turned the bus off and on, light went off and it drove fine.

This continued periodically. Had the bus at the house over the last weekend and when I went to take it back to storage. This time the check trans light would not turn off. Iíve dug through the Allison manuals looking for solutions and couldnít find an easy fix. I ended up taking it to a certified Allison deal for diagnostic. This is what they found, verbatim, from the quote.

ď Tech notes: PULLED UNIT IN BAY CONNECTED DOC FOUND ONE CODE P0748 PCS A ELECTRICAL . OHMNED PCS-A AT THE TCM TO TRANS. CHECKED FOR CURRENT TEMP FOUND PCS-A IS OHMNING TO GROUND/CASE. MOVED HARNESS ALITTLE AND IT NO LONGER OHMN'S TO CASE/GROUND. PLUGGED BACK IN TO TCM AND CLEARED CODE. CODE CAME BACK AS SOON AS KOKO. PLUGGED UP OUR TEST TCM AND RETEST NO CODES SET CLUTCH TEST OK. RECONNECTED OEM TCM AND CODE RETURNED AS BEFORE. LOOKS LIKE THE SHORT TO GROUND ON PCS-A CIRCUIT TOOK THE DRIVER OUT IN THE TCM. WILL NEED TO REWIRE PCS-A FROM TCM TO TRANS AND REMOVE AND REPLACE TCM DUE TO DRIVER FAILURE FROM THE SHORT. ALL PARTS SHOW IN STOCK AT THIS TIME.Ē

Their suggestion is to replace the TCM ($1200, plus 2.5 hours labor) and to rewire and retest the PCS-A circuit from the TCM to the transmission (6 hours labor). All in all, about $3000. This is close to what I paid for the bus and honestly not in the budget.

Iíve seen used TCMs for $200-400 on eBay. Can I buy a new PCS-A and TCM and just plug and play? Fix the current ones? Iím okay with spending a little bit of time and money, but canít stomach $3000 right now.

Any help is greatly appreciated. Thank you all!
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Old 04-08-2021, 09:16 AM   #2
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Join Date: Apr 2021
Location: Columbia, SC
Posts: 8
Year: 2003
Chassis: International 3800
Engine: DT466E w/ Allison 2000
Iím reading how to correct the P0748 code in the manual (http://www.taurusfleetservices.com/images/AllisonTrouble/P4GenT-1000-2000.pdf).

It sounds like, assuming all systems are shot, the process would be:

1. Repair external wiring harness (specifically the J2 harness, right?). The Allison dealer specifically said repair, as does the manual. Can I not purchase a new one? I find the internal harnesses everywhere but canít seem to find the externals.

2. If that doesnít fix it, replace internal wiring harness. Iíve found lots of these available online for under $100 new.

3. If that doesnít work, replace the TCM. The manual advised that the TCM ďusuallyĒ isnít the issue. But if it is, Iíve seen them again for $200-400ish on eBay. I just worry about buying a bad one and not being able to test ahead of time.

Just thinking out loud here. Any input is appreciated!
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Old 04-08-2021, 11:09 AM   #3
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Quote:
Originally Posted by dtsnyder View Post
Hey all,


“ Tech notes: PULLED UNIT IN BAY CONNECTED DOC FOUND ONE CODE P0748 PCS A ELECTRICAL . OHMNED PCS-A AT THE TCM TO TRANS. CHECKED FOR CURRENT TEMP FOUND PCS-A IS OHMNING TO GROUND/CASE. MOVED HARNESS ALITTLE AND IT NO LONGER OHMN'S TO CASE/GROUND. PLUGGED BACK IN TO TCM AND CLEARED CODE. CODE CAME BACK AS SOON AS KOKO. PLUGGED UP OUR TEST TCM AND RETEST NO CODES SET CLUTCH TEST OK. RECONNECTED OEM TCM AND CODE RETURNED AS BEFORE. LOOKS LIKE THE SHORT TO GROUND ON PCS-A CIRCUIT TOOK THE DRIVER OUT IN THE TCM. WILL NEED TO REWIRE PCS-A FROM TCM TO TRANS AND REMOVE AND REPLACE TCM DUE TO DRIVER FAILURE FROM THE SHORT. ALL PARTS SHOW IN STOCK AT THIS TIME.”
My first guess, where I would start that is, disconnect batteries, removing power from ecu/tcm. Don't forget to pull fuses first!

Disconnect the gray and red connectors on the TCM, open them up and visually inspect/clean the pins.
Also make sure all the pins are seated properly and that you can't pull them out. they should have a little locking tab to keep them in place.

If the pins are dirty/corroded or if they do not seat properly I would guess that might be why when the tech "Moved" the harness the trouble went away, temporarily.

It would be a good idea to get a can of contact cleaner and clean it all up real nice since you gonna have it all open.

also, wherever there is a clamp holding the cable in place, open up the plastic loom and visually inspect wires for chafing.

Here is a good video that will better explain what I am talking about.
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Old 04-08-2021, 12:18 PM   #4
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@ewo1, thank you! When I pickup the bus today I’ll pull it into a parking lot and roll underneath and take a look. I’ll bring dielectric grease and contact cleaner with me. Crossing my fingers it’s something simple like this. ��

What fuses do I need to pull?
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Old 04-08-2021, 01:02 PM   #5
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Quote:
Originally Posted by dtsnyder View Post
@ewo1, thank you! When I pickup the bus today I’ll pull it into a parking lot and roll underneath and take a look. I’ll bring dielectric grease and contact cleaner with me. Crossing my fingers it’s something simple like this. ��

What fuses do I need to pull?
In your battery box, there should be either a white wire or a red wire, not as fat as the battery cables. There should be a fuse holder on that wire. It will most likely be for the ECU. Pull that fuse before you do the battery cables. This is to avoid "Noise" or "Spikes" on that line that feeds the ECU.

I am assuming yours is an electronic engine of course.

There might be a second fuse for the TCM but I am not sure where it might be on your bus.

So pull the fuses, unhook you negative battery cable and go to work.

Also, since you are new, firstly...welcome to the site!
And...I posted a whole bunch of service manuals yesterday. I would advise downloading them and as you go forward I am sure you might find things/info that might be useful in the future.

https://www.skoolie.net/forums/f37/d...ual-35598.html

I download everything I can find and then put it all on a flash drive...You never know when or where your gonna break down.
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Old 04-08-2021, 01:04 PM   #6
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Quote:
Originally Posted by ewo1 View Post
In your battery box, there should be either a white wire or a red wire, not as fat as the battery cables. There should be a fuse holder on that wire. It will most likely be for the ECU. Pull that fuse before you do the battery cables. This is to avoid "Noise" or "Spikes" on that line that feeds the ECU.

I am assuming yours is an electronic engine of course.

There might be a second fuse for the TCM but I am not sure where it might be on your bus.

So pull the fuses, unhook you negative battery cable and go to work.
Yup, electric engine, DT466E. What you said makes sense. Iíll keep you posted and thanks a bunch!
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Old 04-09-2021, 08:49 AM   #7
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Engine: DT466E w/ Allison 2000
I picked up the bus last night and pulled into a parking lot and checked out the J1 and J2 plugs on the TCM, per the video above. Everything appeared good to go. Hit it with some contact cleaner and dielectric grease for good measure, but the trans light still remains.

Made the 15 mph drive of shame home through downtown Columbia at rush hour. Bus is currently in storage.

My next step is to pull the TCM and the J1 and J2 harnesses and examine the wires from head to toe for any breaks. Does this seem like a logical next step? Something different you guys or gals would do?

Also, when I picked up the bus they said if I get a new/used TCM it will need to be programmed by the Allison dealership. Is this accurate? The video posted above (and the Allison manual I referenced) both said TCMs rarely need replaced and it’s usually the wires leading to them. Hoping that’s the case here.

Thanks all.
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Old 04-09-2021, 09:33 AM   #8
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The tech notes say it all. If you trust the tech, all of the hard work is already done for you, follow his recommendation.

You had a short to ground either in the connector or wire harness, and that took out one of the drivers in the tcm.

He recommends you rewire pcs-a circuit, and then install a replacement tcm(new or used). Any tcm you install, used or new, will have to be programmed to the bus, in order to get the correct shifting schedules and trans adaptives learned. You might get lucky and buy a used ecm from an identical bus as yours, but the trans adaptive still should be relearned before you take it out on the road.

If his diagnostics are correct, I'd follow his recommendations.

You should tear apart your harness and try to find the broken wire, so that whatever caused it doesn't chafe/break more of them. But I'd recommend the entire wire be replaced from connector to connector, don't try to repair the individual wire, as they're typically corroded from road exposure as well.
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Old 04-09-2021, 10:16 AM   #9
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Quote:
Originally Posted by dtsnyder View Post

ď Tech notes: PULLED UNIT IN BAY CONNECTED DOC FOUND ONE CODE P0748 PCS A ELECTRICAL . OHMNED PCS-A AT THE TCM TO TRANS. CHECKED FOR CURRENT TEMP FOUND PCS-A IS OHMNING TO GROUND/CASE. MOVED HARNESS ALITTLE AND IT NO LONGER OHMN'S TO CASE/GROUND.
Take a look at page 21 of this ATSG allison trans doc.
It will explain in great detail what the PCS is and does.

And here is a link for the entire Allison 1000/2000 service manual.

http://shop.ukrtrans.biz/wp-content/...gs/ALLISON.pdf

Also I am not sure if the trouble code will reset by itself ...
I googled and found this, not sure if it works..

How do I reset my Allison 2000 transmission?




Allison Transmission Transmission Service Indicator Light Reset
  1. To reset the service indicator light.
  2. Turn the key on, do not start the engine.
  3. Move the shift selector to N-D-N-D-N-R-N, pausing briefly (less than 3 seconds) between each selector movement.
And one more gift, a 1000/2000 wiring parts catalog.https://www.stclairtech.com/docs/SCTCatalog2019.pdf
Attached Files
File Type: pdf Allison ATSG pgs 16-21.pdf (948.4 KB, 3 views)
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Old 04-09-2021, 11:55 AM   #10
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Don’t be surprised if you find wiring inside the harness made with biodegradable insulation. AKA RoHS. After you open it up it has a consistency of wet soda crackers. And if you do don't be lulled into thinking that you can cut it off and splice in new wiring. It will continue to decay further up the harness over time. But it is safe for the environment. And afterall that is the most important factor.
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Old 04-12-2021, 12:15 PM   #11
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Originally Posted by dtsnyder View Post
Hey all,

Their suggestion is to replace the TCM ($1200, plus 2.5 hours labor) and to rewire and retest the PCS-A circuit from the TCM to the transmission (6 hours labor). All in all, about $3000. This is close to what I paid for the bus and honestly not in the budget.

....... Iím okay with spending a little bit of time and money, but canít stomach $3000 right now.

Any help is greatly appreciated. Thank you all!
So did you spend the 3 grand ????
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Old 04-14-2021, 01:48 PM   #12
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So did you spend the 3 grand ????
Nope, spent the $300 on the diagnostic and am hoping to figure out the rest on my own. Havenít even seen the bus since bringing it to storage from the Allison dealer.

Was a little sidetracked with my AC condenser on my truck going out (also close to $3k quote from the dealership). Was able to fix that for about 10% of what they quoted me so hoping to do the same on the bus.

Iím heading tonight to pull the wiring harnesses and bring them home to examine. Iíll keep everyone posted on what I find.

Thank you all for the advice. Canít wait to get the mechanical stuff out of the way and started on the build. Iíve got a garage full of solar, AC, water tanks, paint, etc. that would be nice to clear out.
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Old 04-15-2021, 08:49 AM   #13
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So I went to the bus last night to pull the wiring harnesses. There’s a lot more going on there than one would think from looking at the Allison manuals.

Long story short, I was having a hard time delineating where these wires eventually ended to actually get them removed. The baby was waiting in the car with the wife and was upset and I never got to finish pulling the harnesses.

We had a long talk and decided that this particular issue will be awfully time consuming and other projects (moved into our house back in September and have been going nonstop) have taken away time from the kiddos.

Long story short, we’re going to pay the Allison dealer to do the job. It’ll end up being a little less with a military discount and as much as I’d rather use that money on creature comforts in the bus, it will be reassuring having a clean bill of health (and a warranty) on the transmission. Speeding up this project will allow us to paint, get the floors in, and start enjoying it.

Unless someone thinks I’m nuts and has an easy fix? Thanks again, all. Looking forward to posting some actual conversion progress.
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Old 04-15-2021, 09:21 AM   #14
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As a father and husband your family should always come first and other things second, third, fourth and so on. Time is money and the money you spend on the dealer fixing this is buying time for you to do other important things. I do not think you are nuts. I commend you for seeing this.
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Old 04-15-2021, 09:38 AM   #15
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As a father and husband your family should always come first and other things second, third, fourth and so on. Time is money and the money you spend on the dealer fixing this is buying time for you to do other important things. I do not think you are nuts. I commend you for seeing this.
I appreciate that. Weíve been so busy the last four years (three kids, a career change, bought three houses, sold three houses, two travel trailers, a school bus, multiple moves across the US). I have a lot of guilt about missing stuff. Time truly is valuable.

Thanks!
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Old 04-15-2021, 09:54 AM   #16
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AH, guilt--the gift that keeps giving. I'd tell the wife and kids to pound sand etc.

Just kidding, it sounds like you made the best decision.
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Old 04-15-2021, 10:01 AM   #17
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Don’t beat yourself over past mistakes. There are plenty of others that will do it for you. Just correct and move forward and enjoy your accomplishments with your family. When you are done with the bus and the family gets to go see things and learn as they travel they won’t care if you fixed the transmission or someone else did. All they will care about is being with you. Best wishes to you and your family.
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