BOBCAT T770 Switched Power Output Failure

[AGENT86]

I'm at a loss & need some help! I will be as descriptive yet brief as possible but, it's still going to be fairly long. I hope somebody can guide me through this.

2017 Bobcat T770. Deluxe set up. About 310 hours on machine. A few weeks ago right before shut down code M7028 SWITCHED POWER OUTPUT FAILURE flashed up but, everything was working as it should. Before I was able to get back to check the machine was put to use with a cement mixer attachment. About an hour into service the panel showed voltage drop (I was not the one using the machine at the time so this was relayed to me) down to 10.5 volts.

When I checked it with a multi meter thinking it was a battery/alternator issue, the battery was at 12.49 volts. By this time the display showed just 8 volts INSIDE the cab. Then, everything just went dead inside the cab. I could jump the battery at the solenoid & the motor spun full strength, so battery is fine. I checked the obvious things, grounds, fuses, mega fuse, connections, etc.

The unswitched/direct power fuses all have 12 volts on both sides. All the SWITCHED fuses have NO power at all. I swapped the relays, no go. I have 12 volts on the unswitched power wire on the starter switch 12 volts on the blue wire at the switch and when I turn the switch to START 12 volts goes out the TAN starter wire. The SWITCHED ORANGE/WHITE wire has 1.3 volts on it at the key switch all the time, and should have 12 volts when signal/power is switched.

I jumped the switched wire from red power and the display came on. It showed CODE R7404 MAIN CONTROLLER NO COMMUNICATION. That's all I could get off the display, nothing else came on or worked, I couldn't cycle through the menu, etc. IDK if the code 7404 is a true code or if it's because I bypassed something when I jumped the starter switch.

I'm not sure how to test the starter switch properly. It's a 4 pin switch with 5 wires that plug into it. I can't find anything on test procedures. I checked the 3 main harness connectors under the cab. The light & dark gray ones are fine. The black one had 2 loose ground wire connectors which I finally cut on each side & connected together outside of the connector. While doing the wiggle test, I suddenly got power to the cab, but lost it again before I could read the display/see if it was functioning.

Strange thing, when I had power, the headlights began flashing & the headlight relay was acting like a hazard signal relay but this machine doesn't have the hazard switch set up. When I went back up the following morning, the lights no longer flashed and nothing had power again. I have not been able to duplicate the flashing lights, or power restoration. I have gone over the connectors & harness for hours, nothing is evident. I checked for continuity on every wire on both sides of the connectors. The unswitched power wires have 12 volts, The blue wire (monitoring) has 12 volts. I THINK the yellow wire has 1.8 volts but should have 5 volts & goes to the controller.

I want to replace the starter switch just to eliminate the possibility...or am I wasting $?
Anybody have any ideas here or previous experience with a similar/same issue?

 

[Txhayseed]

Sounds like a harness issue to me. We replace a lot of harnesses every year on bobcats.. Sounds like you got a good grasp on the theory. I have had machines that I went wire by wire on and everything checked out but still replacing the harness was the fix even though my meter checks all showed ok. There are so many splices, pins and terminals that it only takes one at even given time to not make contact and you have issues. I cut all the old harnesses out of the loom and save the wire for shop use. There are ground and power splices inside the loom you can not access with out cutting it open. I was surprised the first time how they did it. Just a bare metal crimp inside the loom. Power or ground it didn't matter. Metal crimp right against every other wire. I guess they figure that hard wire loom they use keeps movement inside that its not an issue. You could always run your own unswitched power wire and supply battery power and see if you power up. You did the wiggle test and had it momentarily power back on. So I think your on the right track. Ive gone as far as cutting one harness open and putting it back into the machine on a t650 just because it was bugging me why it was having electrical issues. Everything looked fine but finally after hours of looking installed a new harness and machine had no issues. Still in the fleet out there doing its thing. Its tuff to drop some serious change on a harness with that feeling like your missing something and will find it. But running a external power wire would be your best bet. If your not showing battery voltage for your refer voltage to unswitched power side it has to come through the harness.. Good luck. Ive been down that rabbit hole myself.

 

[AGENT86]

Txhayseed, thank you! for the information & insight. It gives me a lot more useful ideas on how to move forward now. Another thing, based on what I've learned from you about these Bobcat wiring harnesses, it may very well explain another issue that happened a month or so ago. The machine was showing that it was running hot, and began the 3 step warning/shut down mode. I shut it down before it reached the third level, however, an infrared thermometer showed no temps on the block over about 185* when the gauge & display was between 216* and 223*. The following morning, all engine fluid temps were between 56* and 63* except the coolant temp. Before cranking, about 20 seconds after entering the start code, the coolant temp jumped to 130*. Within 3 minutes of running it was in the 216* range. Obviously, the motor was still cold, this was a false reading but the ECM did not know & acted as if it were running hot.

I thought perhaps a faulty coolant sensor, but the issue was sporadic & them just went away on its own. Now, based on what you've told me, it sounds like a harness issue as well. Anyway, I'll be heading back up the hill tomorrow to have another crack at it. So, if I understand your post correctly, I need to jump the power further back than I did at the start switch...perhaps starting at the relay in the fuse box and if it powers up correctly (when I jumped at the key switch it only powered up the display to indicate CODE R7404 & nothing else worked) I should work back down the harness until it doesn't work which would indicate the problem area is forward from my jump point? I guess I should also try to locate any related ground wires & ground at various points to ensure it's not a bad ground wire in the circuit.

Thanks again, I will update when I figure something out.

 

[AGENT86]

UPDATE:
Well, I've made some progress but still not there. It will crank right up & run just fine, but the gauge & display show LOW SYSTEM VOLTAGE so the controls are non-functional (except after sitting overnight...bizarre. Read below for description )The alternator is charging at 14.7 on the orange/white switched power wire but the main battery cable out the back is showing 13.65 volts at the same time. Is that normal?

If it sits overnight, it shows 12.1 volts inside. I can start it up & it actually begins to charge at 14.7 on the VITALS display/gauge. I can move the machine & all controls function for about 2 minutes then the voltage begins to drop off rapidly and in less than 30 seconds nothing works & between 7 and 8 volts INSIDE the cab. I can't isolate the power loss. It's similar to the coolant temp issue, when the gauge/display would randomly climb to overheating & the machine would initiate the shut down procedure BUT the engine was actually running at normal temps based on the IRT. That issue seemed to have just gone away before I could figure it out.

Also, the way I got power restored to the cab was VERY strange. I was testing/jumping wires & accidentally touched a clip from the blue monitoring wire on the keyless ignition switch to the black ground wire on the same plug. (I know) That popped the 25 amp fuse, naturally. I put a new fuse in and was stunned when power came on to both panels & communication was restored with the controller. All I can figure is that when the fuse blew it cut power to the controller & reset it? IDK.

I'm about out of time. We may have to end up calling a certified tech which is going to be big $$ especially since they have to come from TN.

Any ideas/comments/thoughts?

 

[AGENT86]

I believe Txhayseed is spot on about the wire harness. It rained all night & all day today. I went up the hill to drive the Bobcat down to base so I could work on it next to the house. I figured it would take several attempts as I could only run a couple of minutes before the power loss/low system voltage. When I cranked it up the gauge showed immediate voltage loss, it dropped from 12.5 to 11.2 then suddenly began to climb up to 13.8 and remained there. I drove it all the way down & ran it for nearly an hour, It never acted up. I wiggled/shook the connectors/harness, etc. No effect. I turned on the AC and head lights. About 20 minutes in with the headlights on a code M5306...'PRESS TO OPERATE LIGHT SHORT TO GROUND' also, the PUSH TO OPERATE LOADER button green LED does not light when the button is on. It did the day before. There are also two other active codes:
E00067605 GLOW PLUG RELAY FAULT and M6202 TAILGATE FAN ERROR ON.

With all these issues coming then going the harness seems the most likely culprit. I also believe the heavy rain & high humidity are part of the issue creating grounding/current flow in the areas inside the harness that are at fault. I'm going fishing in the morning. It's been too long since I last went. I shall spend more time picking apart the harness to a degree, before I fully commit to a new harness. I just take care of this beast, it belongs to my buddy. Ultimately it is he who must pay for any parts. I hate to see him have to dish out the $$ for a new harness, but if that's what it needs...
I'll update again when I have new info.

 

[Txhayseed]

Be very clear with bobcat when you order your harness if you go that route. That if you get the wrong harness that they ordered for you from your serial number they will take it back if its wrong. I got 4 harness sitting in the shop bobcat said where right based on serial number. One machine took 3 separate orders to get the right harness. I wouldn't think its that hard but I don't work for bobcat and i don't have an issue clicking little boxes on a computer screen. Being that the harness is a " custom" order part they won't take back or fess up to messing up something even though they had the serial # . so I would be clear about that and get someone to say yeah thats a deal before you pay up.

 

[AGENT86]

Be very clear with bobcat when you order your harness if you go that route. That if you get the wrong harness that they ordered for you from your serial number they will take it back if its wrong. I got 4 harness sitting in the shop bobcat said where right based on serial number. One machine took 3 separate orders to get the right harness. I wouldn't think its that hard but I don't work for bobcat and i don't have an issue clicking little boxes on a computer screen. Being that the harness is a " custom" order part they won't take back or fess up to messing up something even though they had the serial # . so I would be clear about that and get someone to say yeah thats a deal before you pay up.

Understood.
I believe the majority of the issue is in the three multi-pin connectors that run from main frame to the cab/controls, etc. Yesterday evening, after ANOTHER afternoon of heavy rain/T-storms, I went through them one last time. I applied dielectric grease to each individual pin, just a tiny smidgen. I found another loose wire that wasn't apparently obvious before. It was a controller ground. Seems it would back out just enough to make partial contact. I secured it & then taped the wires in such a way to keep them from shifting/pushing back.

Before I did this, I ran the machine for a few minutes to confirm still charging & green LED/PTOL light was not working. It did charge but took a few seconds, with voltage dipping slightly. After I completed greasing/taping/securing harness & connectors, the PTOL light was working & it began charging immediately upon starting.

I guess we'll see if it holds up or the harness gets replaced. I'm guessing it'll end up the latter sooner rather than later. I'm going to advise my friend to just buy the harness rather than the wait & see approach. This way there will be no question.
Also, the machine has never had a software update since purchased. I was reading some other threads, is this something that needs/should be done from time to time to prevent glitches, etc?

Thank you VERY much for your guidance/advice.