Mercedes, 3-pedal Autoshift. Engine junk, swapped in a replacement. Freightliner dealer pulled transmission for diagnosis, flywheel bolts broke. We got it back on a pallet. Entire engine harness was swapped onto replacement engine. All wiring seemed to be good, we have one small two wire plug in truck harness on top of trans that doesn't appear to have ever had a home, it's dirty and slightly corroded. I will attach a pic, it's square on one side, curved on the other. These plugs all seem to have a unique shape to prevent wrong placement. Here's the problem. Truck wouldn't crank with the key, trans display stays blank for about 30 seconds, then switches to a horizontal dashed line, after about 5 minutes it will alternate between N and F continually. The secondary buzzer does stop like it did before when the display would normally show N. Upon the advice of a couple different truck guys, we bypassed the system to activate starter, and engine starts. Trans goes into gear, but would then flash 2 and F, 2 and F, continually. We didn't drive the truck because we don't have the hood back on yet. Shut down, nothing improved.
You need to get a schematic from Freightliner, the possibilities are many and nothing but tail chasing. They should be able to provide a transmission harness schematic.
This look like it might be useful?
Of course, we've determined that it doesn't use an actual relay in the Start Enable system, it's determined by canbus signals. So, ultimately, let's just add miles of wiring to diagnose right off the f i ng bat instead of an actual relay we can test and verify power/ground. FML.
Would think that is some kind of gear selector sensor maybe to let computer know when okay to crank. I had a Volvo that had the gear selector sensor went bad in a remote place and we jumped a relay to fool it that the transmission was in neutral so it would start. New junk is difficult. Simon C
So you know, the troubleshooting manual for Eaton Autoshifts was thick and extensive.
The worst of it is it was working perfectly until that forking Mercedes sheared the flywheel bolts. Everything went back together exactly how it came apart, we believe.
Biggest trouble with those harnesses--age and heat, trapped cooking under the cab on top of a hot gear box. Biggest complaint from dealers was break down of harness causing all sorts of communication issues. Food Service of America had lots of those and electrical problems were a constant issue.
The boys solved it today, luckily we have an ancient Toughbook with ServiceRanger on it. Determined that the trans ecm wasn't coming online properly. Dug into the wiring, discovered the eyelet on the end of the power wire in the battery box only had about half the conductors still intact. Fixed that, and we had the trans coming online right away, but start enable relay code, and range solenoid code. After some more investigation, discovered the start solenoid on the driver's side firewall was bad. Trip to John Deere for a new one, now we're down to one code, range solenoid. Found a bent pin in the connector, and everything is fully operational. Moral of this, start at the batteries, and don't assume cleaning the terminals is all you have to do. The schematic showed which wire was power at the trans, and we only had about 11.2 V. Also, without the laptop, we would have had to either tow it to a shop, or pay for a service call.
It is amzing what clean full power and ground can do to a computer in terms of operating. Many have been changed to find the broken wire after. I seen a few times big bosses screaming and yelling to just get a new computer and after some guy being diligent found a loose wire. Glad you folks found it the intelligent way. good for you guys. Simon C
It's also part and parcel for a rig that age and who knows how many hands have unlocked and relocked connections with gruffness. The older the unit the more care has to be taken when handling harness and connections. Glad you found it.