Allison trans / no start power

[WillieB]

I have a 2000 Serengeti M3702 DP that is having some serious electrical issues. I had four new batteries installed and have starting issues. I have no response with the ignition switch, but it has some power at the dash. I can start the engine from the service bay on the passenger side. There is NO power at the trans controller that I can see (even with the engine running from the service bay).

Any ideas would be very grateful!

Bill Brown
2000 Safari Serengeti M-3702
Allison Trans 6-sp

[05wingrider]

You say new batteries - when whomever was in the process of removing the old terminals, did they mark them, or did they rely on color alone to know which wires went to which terminals? Sounds to me like at least one wire (small wire, not main battery ones) isn't connected to the proper terminal. If the wires were connected by color alone, that can lead to issues since (at least on my '96) there are multiple wires of the same color that serve different purposes. Also, there are fuses in some of the smaller wires, and in the process of unhooking and reconnecting, they could have sparked and blown the fuse. There's also a fuse on the bottom of the transmission shift pad.

[TDJohn]

To add to what Duane has stated. On older coaches the engine ECM and the Allison Transmission VIM/TCM are fed by two 10 ga wires, one to positive, with inline fuse for each, the ECM and TCM, that connect directly to the battery positive, and one each for ground, that connect directly to the battery negative. Those wires can easily slip back into the plastic loom and be overlooked. I would check for those wires, you should have four of them, or non of them, so if you only see two or three wires, start looking for a wire that escaped. Being that your coach is newer, it is possible that your coach, as the newer ones do, might have a very small fuse box in the battery compartment that has those fuses located in that box, among a couple of other fuses and some relays. This box is usually black and blends in, so it is hard to find. If you do have one of those fuse boxes, check those fuses. Worst case scenario, so you don't pay crazy labor rates to hunt for a missing wire, run a new wire, with an inline fuse, to the TCM or VIM . If memory serves me correctly, it feeds into the VIM (thick black box, use google for image). You state that not all items are working on your dash, so it is possible that your solenoid that energizes the 12v dash items when the ignition is turned on, has failed or is not receiving the signal when the key is turned to the on position. So the ignition switch, and solenoid operation need to be checked and verified that they are working properly, as the Allison computer system gets two power sources, one that is constantly fed to the VIM and the other that is fed only when the ignition is turned on. If either signal fails, it will not let the engine start for safety reasons, because when the computer is not turned on, it can't verify that the transmission is in neutral. By starting the engine from the service bay, you are essentially bypassing the transmission computer. So both have to be checked and verified.

[WillieB]

Thanks for all the information! We couldn't figure it out, so I had the local Allison repair tech come out and found the issue. All his computing work came up with a missing ground in the battery bay. The power wire for the TCM was connected to the ground !! Once that wire was connected to the positive battery, everything came to life. The coach now starts as it should!!