JoeH Posted January 10, 2022 Share Posted January 10, 2022 2003 MR688S AI350 w/ Allison HD4560 trans. (see post in Modern Truck section to see what we've done) got frame rails back in, everything (I thought) is hooked up. No power to the trans controller, thus not allowing us to crank the engine. (Got it to fire up by jumping a solenoid). Runs but won't go into gear as there's no power to the gear selector! Truck has a ton of hours on it, so needless to say wiring has been "repaired" by former owners a time or two. There's a makeshift power wire coming off ignition terminal in dash, T's into a wire in the gear selector harness. This wire has power when key is on. (According to my dad, I haven't verified. Will do so tomorrow.) Assuming it's getting power, where does it ground? This tiny power wire seems hardly sufficient to power "everything" so what else should I be looking for? Also note it has Blink Code 6-8, which indicates a failure in the J1939 serial data link, which is 2 wires twisted together (to obscure any potential interference,) running from the VECU to the Transmission. Would a break in this link cause the above No Power fault? Quote Link to comment Share on other sites More sharing options...
JoeH Posted January 11, 2022 Author Share Posted January 11, 2022 After a day of beating my head against the wall, I have determined that Pins 1 and 16 on the "grey" "V" plug on the Allison ECU don't have power, when they are supposed to. Allison wiring schematic shows a 10a fuse, but it's on the Vehicle side and I don't have a diagram showing me where this fuse is located.... I'd love a fuse location diagram for a 2003 MR688S if anyone has access to one... Or could provide any insight as to where fuses/breakers are for the auto trans... Quote Link to comment Share on other sites More sharing options...
880joe Posted January 12, 2022 Share Posted January 12, 2022 I had an 07 CHN with a fuller autoshift that did something similar to what you described the fuse was down by the starter on it Quote Link to comment Share on other sites More sharing options...
JoeH Posted January 12, 2022 Author Share Posted January 12, 2022 I'll have to sift through all the wiring to find it... Currently I'm looking for the "VIM" as Allison calls it: "Vehicle Interface Module", a series of ~6 relays, a couple 10a fuses, and a couple other odds and ends. Probably need to just grab a 10a fuse and start swapping it for 10a circuit breakers to see if I get a positive result.... Quote Link to comment Share on other sites More sharing options...
JoeH Posted January 17, 2022 Author Share Posted January 17, 2022 (edited) Fuse wires at the battery box never got hooked up after frame reinstall. Now I have a Crank No Start with blink code 6-4. Need to delve into voltage fluctuations under start conditions for the EECU and VECU... Apparently it's an issue, and there's a service procedure to add supplemental power from the starter relay to the 3 EECU 12volt inputs. Edited January 17, 2022 by JoeH Quote Link to comment Share on other sites More sharing options...
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