Allison HT 748 Atec Parts Help

NeoplanAN440 · January 23, 2010, 06:26:08 PM

Comming back from CA with a loaded Trailer my Transmission decided to go two times into a kind of Limp Mode!No Lights on the shifter panel and no reaction on pushing each range button.First time i had to kneel to reset my atec.second time i had to turn off and restart to get in gear.
this happened both times when we stopped and had to park for a minute in idle.(to dump or to ask for directions where we can park overnight)
we had some do not shift light problems last year.do not shift light on with no reason.we got his bug out by fixing the kneeling circuit and the level valve.

any sources here where i can find a ecm and a shift pad.any bus yards known that have flexibles or neoplan with an440 in the NM,AZ,CA area??

Trying to look ahead and get me a spare ecm and pad,if this gets worse.

NJT5047 · January 23, 2010, 08:16:54 PM

An Allison HT748 will store fault codes. Before buying an ECM or pad, the codes should be downloaded and digested.
You'll probably find a bad ground, loose wire, loose fuse, or faulty power supply to some trans related components. If it'll shift in 'limp mode,' and move the bus, some of the system is working.
The transmission proper is more likely to fail than are the electronics.
If you find no codes stored, that likely indicates no 'trans' problem, but a wiring issue. These sorts of faults are a hoot to locate. Still, replacing ECMs without some good reason probably won't solve the problem.
The kneeling system is a PITA for DDEC/ATEC units. There are multiple layers of interlocks when the kneeling system is engaged.
A Neoplan wiring schematic would be a good place to begin. Checking (maybe swap them around?) all the relays, fuses, fusible links, and circuit breakers, and transmission related wiring multiconnectors involved in the kneeler might be a start.
ATEC ECMs are rather robust. They rarely cause problems unless...say 24V are applied to them in error. Wiring problems are endemic.
In any event, I doubt that shift pads and ECMs are Neoplan items. The correct series Allison parts should interchange between coach brands.

Good luck, JR

NeoplanAN440 · January 23, 2010, 08:52:27 PM

thanks njt

yes the kneeling circuit is a story on its own.i got the neoplan wiring diagram!
but like most systems my bus is a little different or they changed functions.
also i guess because it had a wheelschairlift.thats gone now and replaced by a one piece door!

i checked all the wire connectors and ohmed all of them out.we also had the harness removed,as we put both transmission and bus harness under the coach to have it out of the way for the interiour.
removed tranny pan and solenoids ands connector plate looked good.
if allison made it the same as neoplan (splice connectors embedded in the harness) i guess you are right and im chasing for broken wires!!

im kind of dreaming to find the same bus,to take out the ecm,pad and harness to have time to take it apart and have spare parts,while still on the road meanwhile.

i tried the friendly allison dealer for code reading.(no names here as im still not happy with the service)
no codes,and the answer is its a computer glimpse!!

looks like i will keep on chasing

luvrbus · January 23, 2010, 09:40:45 PM

Check with Kim 1-888-395-1392
www.aztranny.com
he also has a trouble shooting guide for electronic transmissions on his web.

he is located in Tuscon AZ

good luck

Tom Y · January 24, 2010, 05:50:19 AM

I saw a shift pad on Ebay in the last few days. Not sure if it will work for you. Tom Y

Sean · January 24, 2010, 09:57:24 AM

I agree that your ECU is not likely the problem. Also, you should be aware that it is not as simple as just putting another ECU on; each ECU is specifically programmed for the application. You will need to have an authorized Allison dealer upload the program from your current ECU and download it into the replacement; IIRC, that will cost you at least a couple hundred, even if you got the ECU for free.

The place to start is with fault codes. If you wait until you get to the dealer or someone with a reader, the codes will be gone -- Allison CEC-1 codes do not persist after a restart or a shift into reverse. However, you can check the codes yourself as soon as the trouble occurs.

First off, you need to make sure your "Check Transmission" (CT) light is working properly. This is not on the shift pad; instead it is on the dash and should display "Check Transmission" or similar wording when lit. When you first turn on the ignition key or master switch, this light should come on for about 2-3 seconds, then go out. If the light does not come on at all, that's the first thing to fix. I can probably walk you through that.

Once you are sure the light works, note whether or not it comes on, either intermittently while driving, or steady when this problem occurs. Again, if the light does not come on but you still have a problem, that will tell us where else to look.

You will also need to find the diagnostic connector for the tranny (may be the same as the one for the engine, or they may be separate). It will have two rows of 6 pins each. Once your CT light comes on (even if it later goes out), you will short two pins on this connector together to flash the trouble codes out on the CT light. I don't have the specific pins handy in front of me (perhaps someone else can jump in here with the right pins -- Pete RTS/Daytona?), but if we get that far I can dig out my CEC troubleshooting manual and give them to you, or look on my own connector (I also have a 748, but I actually installed a switch to do this whenever I need to).

One final note: I have found that similar problems can occur due to poor seating of the Canon plug on the rear of the shift pad. Double-check this connector, as well as the two rectangular ones on the ECU itself.

-Sean
http://OurOdyssey.BlogSpot.com
(Neoplan with HTB-748)

NeoplanAN440 · January 24, 2010, 10:13:09 AM

thanks for helping

i never had a transmission check light. it comes on only on lamp test at the cluster.never comes on when turning the master switch.i will get a do not shift light and a warning buzzer for about 3 seconds,when i turn ignition on.then it goes away and shows N.after that i can select my ranges and drive for ever.it only happened when i stop and go to N to idle for a couple of minutes.when i came back and wanted to select D,i got no reaction.first time i got the shift signal and it showed the red light for d,but no gear.second time the shift pad was blank and no sound.

if somebody can get me the the two pins to activate the read out,that would be great.
i will double check the check lamp wiring.

Sean · January 24, 2010, 11:43:17 AM

OK, I pulled out the book. (If you continue to have problems, you probably want to get a copy, available from any Allison dealer.)

Pin B on the connector (wire 216A) gets grounded to initiate code readout. You can ground to the chassis, or just jump it to pin A, which should be ground for the diagnostic reader.

Wire 215 drives the CT light. This is a grounding signal, so it should go to a relay; the other relay coil wire goes to +24v from the ignition. The ECU grounds this lead to illuminate the CT light. I checked mine; the light illuminates for one second when I turn on the master switch.

The light itself is then driven by the relay contacts; you'll need to hunt around to find out if the relay switches the ground or the +24v. I'm guessing it's the ground, and the lamp test button grounds it as well.

You might find this relay is bad, missing, or has a loose connection. Start there; without a working CT light it's hard to diagnose anything further.

There is one other possibility, which is that the +24v to the relay coil is provided from an oil pressure switch, so that it is only hot while running. Not uncommon, but it defeats the self-test.

If you can't find a problem with the CT light, we can force a fault code to make sure the light is working.

-Sean
http://OurOdyssey.BlogSpot.com

NeoplanAN440 · January 24, 2010, 01:07:51 PM

thanks
i will go on it first thing on monday.
need to be on the road as soon as possible without worries!!
nothing more funny then standing in line at the dump station and telling everybody,maybe im standing longer here(haha)

hope i can bother you more monday evening when i have the results!!!

the reprogram cost at the dealer was exactly why im searching for an identical bus to get the parts from!!
problem here is also that they changed mine from ht740 to the 748,but kept the mui engine.
so i only have a throttle position sensor as comm to the engine.
i guess the 748 shifts way smother on a ddec engine.

that got me to the ideas changing to a manual transmission.its not the same fun,but grown up on trucks,i think i can handle a few more miles shifting!!!
also pulling my trailer,gets me still looking around for a cummins or.......

i dont need speed,but sometimes at long grades the trucks are getting pretty fast bigger in my mirror and you wish this is not a roockie on his first trip out!!!
it looks like a bus is never finished!!!

thanks for the help and great advice

sorry for the post on the generator part,
but living off grid and having my fight with power companies,gets you playing and trying,forgetting that some people cant split what can be done legal and whats unsafe!!
im just mad how some solar installers tried to make a fuss about a common system.
instead they should teach and explain and take the scare away from people interested in it!!

belfert · January 24, 2010, 01:20:54 PM

I doubt the shift pad is your problem, but a company in Hibbing, MN rebuilds them for about $250. I think the name is Diesel Electronics.

NeoplanAN440 · January 27, 2010, 12:10:04 PM

Back on my Atec Problems!!
I hope Sean can kick back in,as he was already more help then i even expected from this site!! Thanks

sometimes i need somebody that tells me to go on troubleshooting!!! its just to easy to say i do it the next time i have problems!

I got the Check Light to work again!! It comes on for about one second after i turn the master or on Lamp Test.If i try to read codes nothing happens!!

Should there be a 12 (like on Gm) or any other code if the ECM is clear?

Took the bus out,to warm him up for his oil change before he gets onto my ramp.
did a couple of stops,shifted to N and idled for a minute or more.
nothing!!!!!
moved all the connectors while on the ramp,twisted all the areas of the harness underneath the bus!!
Nothing!!!!!

so i guess i have to wire also a switch to get codes on the spot!!!
but first i need to know,is there a clear code (like the 12 on GM)
otherwise im in for the next search!!!

I found the Manual SM2004EN on the Allison website.is that the same you have?

Does it show also the Trouble Codes???

if so i guess its worth a million to get and have it with me!! as for now i have only a wiring diagram that was added to my Neoplan service manual.
Let me know if its the same manual,then i will try to order it!!!
Lets hope its not taking as long,as my last internal Transmission Filter and Gasket!

Sean · January 27, 2010, 06:10:05 PM

Quote from: NeoplanAN440 on January 27, 2010, 12:10:04 PM
I got the Check Light to work again!! It comes on for about one second after i turn the master or on Lamp Test.If i try to read codes nothing happens!!

Should there be a 12 (like on Gm) or any other code if the ECM is clear?

No. If no codes are stored in the ECU, the light will not flash at all. There is no "all clear" code.

Quote
so i guess i have to wire also a switch to get codes on the spot!!!

This is exactly what I've done. If I get a CT light while driving, I just press my momentary switch to read the codes. I've got a touchy oil level sensor, so I get a code 12 periodically (which is low fluid on most 748s)

Quote
I found the Manual SM2004EN on the Allison website.is that the same you have?

No. The manual you need is TS2712EN, Allison Commercial Electronic Control 1. It's very old; my copy was dated 1994 and published by GM (even though I bought it new in 2002).

Quote
Does it show also the Trouble Codes???

Yes. However, the list of codes is also easy to find on the web, or I can tell you what they are if you get one. Still, I suggest buying the manual -- worth the hefty price, especially with the problem you are chasing.

-Sean
http://OurOdyssey.BlogSpot.com

NeoplanAN440 · January 28, 2010, 08:00:21 AM

Thanks a lot Sean!!!!!

Looks like i have to wait,till i run into the Problem again and then flash the codes!!!

NeoplanAN440 · January 28, 2010, 08:33:37 AM

One more thing!!!

while testing and trying to get the problem back,i realized that i get the do not shift light and the check light as normal when turning the master switch on!
but every third start or less i also get the warning beep for 3-4 times!!

another problem to chase???

i just cant sit and wait till i get the book!!!

Sean · January 28, 2010, 08:42:40 AM

You will get the warning beep when a real "do not shift" condition exists (as opposed to the start-up lamp test). That can be as simple as the High Idle being on, TPS counts high, or similar condition. If it happens intermittently, see if you can track down what's changing between starts, such as High Idle, emergency brake position, throttle position, etc.. The ATEC has its fingers in a lot of pies.

-Sean
http://OurOdyssey.BlogSpot.com