Wierd Allison 740 issue...I'm defering to the experst here!

[rgrimard]

Hello...this is the first time I've ever posted here on the forum. Usually I just read posts and learn from other experts...unlike myself . However, I have a question that I hope you may be able to shed some light on or at least point me into the right direction. I have a 92 MCI-102c3  with a Cat C-10 and an Allison 740. My question is this...Last weekend I drove about 800 miles without any issues coach worked flawlessly. This last Thursday I decided to get some fuel so as to top the tank off. When I started the bus, the "check trans light" did not go off but the transmission still went in to gear and ran perfectly. I checked the fluids and all was fine but the light stayed on. Today when I fired it up (since I'm bringing it into the shop this evening)...It went into reverse but will not return to Neutral unless I shut it off then it defaults back to Neutral. have any of you ever heard of the bus not being able to return to neutral from any of the drive positions? I'm bringing in the bus tomorrow but I was trying to learn as much as I possibly could prior to this
thank you in advance
Ray

[eagle19952]

this is a pad/button shift ... ??

[luvrbus]

1st you probably don't have a 740 it's probably a 748, but some how it is in the diagnostic mode be sure wire 222 has a good ground and check wire 215 it needs a good ground also if wire # 216A is grounded it goes into the diagnostic mode.Do this 1st stop the engine and turn the test switch on and restart the engine   

Do you have a Prolink to check for the hard codes ? the 700 series ATEC can be a nightmare to chase down the problems

good luck

[rgrimard]

Thank you very much. I will do the suggested procedure. Wow what a great resource you guys are. Oh it is a push button shifter.

[rgrimard]

Sorry for the apparent carelessness...but where is the test switch you are referring to?
Thank you for taking the time to respond
Ray

[eagle19952]

Sorry for the apparent carelessness...but where is the test switch you are referring to?
Thank you for taking the time to respond
Ray

i am super old school...linkage/cable only. BUT I think the test Sw is either a sequence of buttons on the pad or a stand alone sw on the shift pad...

mode maybe.

[Scott & Heather]

I have the same tranny in my 102C3. The ATEC system is kind of quirky. Definitely
A 748


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[rgrimard]

How do I get this shifter to clear or give me the fault? The selector does not have a mode button just r,n,d,1,2,3. There is a red display but how do I activate it with this shifter?

[Scott & Heather]

Free bump. Anyone helping you out yet?


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[luvrbus]

Scott, where is your test switch located on the MCI C most are in the pad or shiftier area,do you have a pad or shift tower? I gave my owners manual to a person and what he needs is OM1957EN manual to tell him how to retrieve the codes from a tower.I never done it with a tower I used the Pro/Link, the 700 series just has soft and hard codes the hard codes takes a Pro/Link I know that for sure 

[Scott & Heather]

Well, my C3 bus is in Michigan and I haven't been home in a year. Will be there in a few weeks tho. I think my test button is elsewhere cause I haven't seen it on the shift pad. I do indeed have the pad not the tower.


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[jackhanow]

Not sure if the tranny diagnostic is in the same place but my manual say the engine diagnostic switch is located LH rear baggage compartment behind panel on tunnel and in a hinged box right of the drivers seat at the junction of the floor and drivers modesty panel. My manual basically says , yup , you got a tranny .

[jackhanow]

My other book says by the ac switch by the dash. I have an 86 and it doesn't have that.

[jackhanow]

So the first book says hold the switch on and count the blinks short pause is the next digit 2 digit per code I have the chart

[solardude]

rgrimard

I have almost the same setup as you. The switch Clifford is referring to is in the third bay, inside a hinged cover.

However, you can retrieve the codes by simply turning the ignition to the first position, then press the diagnostic button on the left hand panel. It's a rocker switch, press it one way and it will start blinking the check engine codes, press it the opposite and it it should blink the trans codes. If your check trans light is burnt out, you can still listen for the relay clicks. If there are codes stored, the TCU will blink/click the codes one after the other. It can be confusing though as some of the codes are double digit. If you don't here the clicking or see the light blinking, you will have to use the toggle switches in the third bay under the cover on the drivers side. Be super careful not to disturb the wire harness too much. You can really make a mess for yourself if you knock a wire loose. I try to only move wires on either the ECU or TCU when I need to.

Last but not least, if your shift pad is working correctly, you can clear the TCU codes by again turning the key to the first position, and shift repeatedly from D to N till you hear a high pitch sound.

I currently have a bad forward pressure switch I need to work on, so I know that when the trans stops going into gear I need to clear the codes in order to get the trans to go into gear. So far if works every time... I hope to get the time to track down the problem before it worsens.


I don't know where you are, but be super careful who you let work on your trans, there are not a lot of shops that are competent with the ATEC trans and often cause more harm than good.

Pull the codes and post what they are and I may be able to help further, or perhaps a REAL expert may chime in.