We have 2 of these with the same symptoms, One thing I did notice is using the Dearborn diagnostics software I had an erratic signal on the 1708 bus. nothing on the 1939. hooked up to a M984A4 (similar powertrain) I had signal on both. We've pulled the speed sensor out of the transfer case cleaned and re-installed it. no change. Schematic shows the VSS feeds directly into the CAT ECM. So the Cat ECM converts it and puts it out over the databus. I've checked both the terminating resistors on the bus and they are both with in spec. As well as total circuit resistance for the J1939. I have gone through the wiring harness and all the cannon plugs looking for anything else wrong (bent pins, rubs, etc) and come up with nothing. I have pretty much arrived at the conclusion that I need a new ECM. Does anybody have any other ideas?
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