Quote:
Originally Posted by ewo1
Sorry but i had to reformat your post, it was hard as hell to follow and understand as you wrote it all as one breath! give us old guys a break please!!!
I have been researching Allison 2000 TCM wiring diagrams and I can't seem to find one that reflects the TCM having secondary i/o ports for accessories such as wheel chair lift or PTO's.
From what I understood from Cadillackids explanation in another thread, yes the 2000 tranny will stay in gear and drive up until you slow down or stop then it goes into limp mode.
One thing that stands out from his explanation is the the locking convertor within the trans will not lock and long term abuse can negatively affect the tranny.
If anybody here can explain how the wheelchair interface might be wired up to the allison 2000 TCM please chime in and share.....
Here's a thread from last year where someone describes a similar situation as yours, not saying this is your problem but it is worth consideration within your troubleshooting thoughts.
So I found within the troubleshooting manual for a 4th gen 2000 the section that identifies that yes, the 2000 TCM does have configurable i/o ports.
What I am missing from my manual is the Appendix section, section M to be specific. Manual number is TS3977EN.
If anyone has this can you please share....
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so theres a lot of bits and pieces here..
1. an input or output will NOT limp the tranny or disable the lockup (unless said inout sends it to a non lockup shift schedule or one where lockup doesnt engage till a higher gear.. thats something ive never seen on a school bus)..
2. an input can be set up to turn on inhibit mode which means it wont go into gear.. this is on the transmission side nothing to do with the engine.. such uses might be a wheel chair ramp down, a park brake still applied, or a bucket truck boom still deployed, etc.. anything where you might want the engine running but not want the driver to be able to move. you may have an inhibit light with nop check trans light.
3. a J1939 data-link failure will NOT limp the transmission in and of itself.. since the transmission has no ability to tell how much throttle is being applied it will disable the lockup converter.. with the lockup disabled the transmission estimates the amount of throttle being applied by how much torque coinverter slip / spin it sees.. if you are pushing hard on the throttle you'll typically see more difference between the engine RPM (RPM speed sensor).. and the turbine speed inside the transmission.. this is important as that is how the transmission modulates its shift pressures and shift feel.. much like we have talked about detroying an AT545 when the modulator is bad or unplugged, due to shifting under full throttle with low pressure.. the allison electronic transmissions need to know the throttle being applied.. normally this is through either a directly connected TPS (mechanical engines to electronic transmission) or via the J1939 Datalink.. (the engine computer tells the allison how much the foot is buried in a number 0-100%). check trans light comes on during a J1939 data link failure.
4. in a limp scenario.. Limp means the transmission has incurred what it considers is an error severe enough that it cannot continue to function in any kind of a normal manner.. if it can maintain the current gear in any capacity it will do so until you slow down.. it is looking to get to its "inhibit-mode" gear.. which on 99% of these allisons seems to be 3rd gear... it will only habve that gear.. it will be a total dog coming off of a stop and will not shift at all so you'll reach maximum speed fairly quickly.. it doesnt seem to ever call for lockup during limp.. you likely will have a check trans and an inhibit light on at this point.. it *IS* possible that the transmission cant maintain any gear and will just neutral out.. this happens if it starts seeing slips say from a massive fluid leak.. the fluid pressure is dropping and its slipping badly in the current gear so it just gives up at that point , neutrals out, and you have no more power from it at all..
5. that said.. if you read the input output guide for the allison.. Most inputs (called wires in allison speak) have a J1939 datalink datapoint as well.. so its possible that the pins on the TCM for an inout may not be connected yet the transmission still receives an inhibit vis the datalink from the ECM or BCM... at one time I had the full IO guide for allison now i cant find it.. not sure what I did with the PDF its someplace i just likely named it something I cant find... it talks wire by wire what each inout and each output does and also the J1939 PGN/SPN of each... ill find it again one of these days.. I have sent J1939 gear selection commands to my T-handle allison 1000 and made it act just like it has a touchpad.. (in fact I even used Module ID 5 which is a keypad and talked to it ..and it worked..)
6. certain engine manufacturers may have their own circuits for body builders.. on IH the bodybuilders guides talk about some of it.. on modern busses it goes through the BCM... in.the case of IH on the older busses they had starter-inhibit circuits to the ECM (not the datalink).. if said circuit wasnt proved then you could turn the key but would get no cranking... these circuits would be separate or in addition to anything it does to the transmission for say a lift down.. I believe on newer busses with the wabco hydraulic brakes the wheel chair lift down disables the ability to release the parking brake as well as sends a signal over the datalink to tell the allison to inhibit in neutral. inhibit mode can apply to transmisisons with T handles as well as pushbuttons..
Linear Mode
