BOBCAT T770 low voltage issue AGAIN

[AGENT86]

Hey all. Had a similar issue with this machine a couple years ago. I eventually found a couple of issues (bad connector pins on cab harness & corroded mega-fuse connections) and up until now it's been running well. This time it's very similar except it doesn't loose all cab power. Basically, it starts & begins charging as it should. After anywhere from a couple minutes to an hour or two the voltage on both displays drops off from a charging rate of 13.5 to 14.5 down to eventually 6.5 volts. It takes a while to get that low, but once it drops below 11 volts the LOW VOLTAGE code kicks on.

The controls are dead once the voltage gets too low. It'll sit there and run just fine though. The alternator is still charging as it should when I test at the battery AND all the switched/unswitched power wires, etc. I can't find ANY wires indicating a voltage issue, INCLUDING the wires that feed both display units.

My question, if BOTH displays are receiving proper voltage at the connectors how do they show such low voltage? Do they get the actual voltage input from another source, like the ECM instead of a direct feed off the alt/battery? Is it possible one of the displays are faulty? With the engine off & key on the voltage will fluctuate between 6.5 and 7.0 volts on the displays.

It has a brand new NAPA GOLD battery. I just replaced the solenoid for the air intake heater. It was shortly after replacing the solenoid that this began, although during the winter upon startup the battery volts would stay at 12 volts after starting for up to a minute or two then suddenly begin climbing into the proper range. That was with the old battery which turned out to have some bad cells.

Anyone have any ideas/similar experience....?

 

[AGENT86]

One other thing I noticed. Upon shut down, when the display was showing 6.8 volts, when I switched the engine off, for a brief second just before the screen went black the voltage jumped up to 10 volts . Not sure if that indicates/means anything.

 

[ozarkag]

Voltage is likely measured at that mainframe controller, and the displays are only displaying the reading.
I had an S185 suddenly not start witha low voltage code, ended up being the controller.

 

[AGENT86]

Thanks for the reply, ozarkag. That's what I'm thinking. I wonder if the controller can be sent off for testing without being on the machine? I'm really far away from the nearest Bobcat dealership/service shop. It has less than 400 hours on the machine.

 

[ozarkag]

Try www.isoscell.com 14012033222
They are the only place I know that can test and repair Bobcat controllers.

 

[AGENT86]

Great! I'll give them a shot. I'm going to spend a bit more time on it as soon as the weather breaks. I'm learning more about the CAN communication & unless I find anything obvious I believe it very well may be the controller, as you said. I'll update when I figure something out.

 

[AGENT86]

Ozarkag, when you say the mainframe controller, are you referring to the ECM or the Gateway Controller?

I contacted isocell. Unfortunately they don't work on the two plug ECM which is the one I have, nor do they work on the Gateway. I had the ECM and Gateway controller out, checking wires/connections, etc. With the ECM unplugged & Gateway controller unplugged, nothing on the displays, of course.

With the Gateway controller connected & ECM unplugged the displays function & show voltage. So the displays get the voltage info from the Gateway controller, it would seem to me? I ran the machine and after aprox 10 minutes the voltage drop began. The drop is always the same once it begins, steadily dropping until below 12 volts & eventually dropping into the 6 volt range. The initial drop from 14.2 to below 12 volts takes less than a minute.

I would be inclined to believe the Gateway Controller MAY be the problem. However, I just got the factory service manuals with wiring schematics. There are several in-harness resistors besides all the splices, which Txhayseed had enlightened me about back in 2022. With the schematics I can see what he was talking about. So, it's possible the issue could be with the harness. However, with under 400 hours, hopefully not.

I'm looking into the Bobcat Diagnostic Analyzer which should allow me to see what's happening in real time? It also allows updates, which has not been done since 2018 when a service tech from Bobcat was here to address a no-communication with controller issue. That was a couple years before my arrival.

That Gateway Controller is $940.00 from Bobcat. If it turns out to not be the issue, then we've got a 'known good' unit for backup.

Thoughts & comments appreciated!

 

[ozarkag]

Gateway also known as mainframe controller. I've had isocell do the G series mainframe, and on that one some are repairable, some are not.
A steady drop like that does make one suspicious of a controller. If you do replace it bobcat will have to program it on the machine.

 

[AGENT86]

So the diagnostic analyzer from Bobcat would not be able to program the new Gateway Controller? From what I've seen it can be used to update everything on the machine. Of course the current software would be required. To program a new/blank unit would require proper software as well, so if Bobcat has to do that it means only Bobcat has access to that particular software?

 

[ozarkag]

Where would you be getting the Service Analyzer? As far as I know a hacked/ blackmarket version of Service Analyzer will not include payload files, or whatever Bobcat calls the actual software for the controller. Only a dealer will have access to the download required.

 

[AGENT86]

Most likely from Bobcat. unless we can find one from a reputable source for a better price. Possibly even a used one. However, if it still has to go to Bobcat for programming then it wouldn't be very cost effective to purchase one other than for future diagnostic/troubleshooting issues.

 

[AGENT86]

UPDATE....problem solved.

Bad Gateway Controller.

I called Bobcat of Asheville yesterday & spoke with the service rep. I explained the issue & my thoughts on it being a bad Gateway. He agreed that seemed likely. They had a new gateway in stock & amazingly had an open slot to send their service tech today.

I agreed that the tech should run diagnostics & check out all other possibilities before just installing a Gateway. I did learn that the voltage readings do indeed feed the displays via the orange/wht switched power wire from the Gateway. That's what was causing some head scratching as the voltage was 14 volts at both displays while running but still showed low voltage/dropping voltage on both displays.

The tech repeated many of the same checks I had done as well as a few I hadn't. The diagnostic analyzer showed everything as 'normal' and gave step by step things to check. The final word from the analyzer read that the Gateway Controller shows no fault related to the issue & likely a faulty Gateway.

The tech installed the new Gateway Controller, programmed it on the machine. The displays showed charging at 14.2 continuous with no drop in voltage...problem solved. The machine actually idles smoother & runs quieter now. It seems like a different machine. It's not my imagination, it's VERY noticeable.

Thanks again, ozarkag for your input. Also a shout out to Bobcat Of Asheville & Terry in the service department & Ricky the tech who came out to repair the machine. These guys know their stuff!