Were you unable to get both rear wheels spinning in manual VTM-4 lock with VSA disabled?
We were not. The truck was in very slick mud on the entire driver's side, both driver's side wheels were spinning, neither passenger wheels would spin. We dug out both driver's side wheels and slid some sticks underneath for traction, then one pushed while the other drove and it managed to just barely pull itself out. I was under the impression that VTM4 would send some torque to the passenger rear wheel to get us out, but, at least in this situation with this truck, it was not able to do so.
But if it were a silent failure I would not expect the rear driver's wheel to spin. I guess maybe clutches on one side could be in the process of failing and can only transmit a very low amount of torque. We worked through the entire process, tried to get out of it, shifted it into 2 and locked in VTM-4 and tried, next tried simultaneously depressing the brake and using the ebrake to trick the diffs into seeing more traction on one side, then disabled VSA. In the end it took clearing out some mud and putting down some sticks for traction on the slipping wheels and bracing against a tree and pushing it very hard. I don't know how much the pushing really helped, but that's what was happening when the truck broke free. It was a good experience for my friend, who now keeps better traction aids in the trunk. Nevertheless I hope that never happens again. When you stop going forward and start sliding sideways down a hill, because you hit slick mud you couldn't see, it gets a little scary.
I agree with Speed's observations, and in my opinion, this truck was NOT functioning properly. There's no way that both wheels on one side should be not spinning ("neither passenger wheels would spin"), even if you did NOT have VTM4 locked and was in Drive.
I cannot explain your observations short of some type of failure in the VTM-4 system. Maybe someone more knowledgeable will chime in with a solid explanation.
Actually, there is a procedure. It involves manually applying voltage to each clutch and trying to turn each wheel.
We did not try manual lock in "1" at all. I told him to go to "2" because I figured the additional torque to the wheels in "1" would do more harm than good since we were spinning wheels anyway. In "2" we tried with both VSA enabled and disabled, and with and without applying some brake pressure to try and trick the differential into "seeing traction" on the driver's side. It seems that the stability control, at least in this case with this vehicle, is not sufficient to send torque to the side with traction. This was a particularly tough situation though, it wasn't just a little mud, we slid sideways down a hill and nearly crashed sideways into a treeline. The driver's side was probably close to a completely zero traction situation, like they get on those rollers you see on internet videos sometimes. We never would have gone that way if we had known what it was like, but the grass was relatively high and it hadn't rained in several days, it was one of those fluke situations where it came completely out of left field.
This is a really good idea. If the Ridgeline were still mine I would probably give this a try. Pretty sure my friend won't be interested though. So each wheel should be capable of putting down 148 ft lbs of torque when the system is fully engaged? Interesting.
I'm not so sure Speed.... I might be missing something, but at section 15-45 in my 2006 Service Manual, I'm looking at "Differential Function Test", which utilizes the HDS diagnostic unit. It tests the electromagnetic coils in the rear diff + ??. The manual just says "follow the screen prompts", so I'm not sure exactly what the procedure is or what exactly gets tested. Result options are only "normal" or "abnormal" (in which case the solution is to replace the differential)!
Yeah, it was the "follow the screen prompts" part that left me unsure what they were actually doing during the test (which might have tested for ???). I guess I'm granting too much benefit of the doubt. (Yes, that's the test I was referring to)
That last uncertainty is the troubling part of trying to understand/diagnose what's going on with VTM-4 in various reported situations!
Yes, Sorry I wasn't clear. I have never manually engaged the VTM-4 lock. My bad
That is pretty much my understanding. And in addition, if the wheel with traction is not turning (in a perfectly functional system), that would indicate the clutches in the VTM-4 unit are slipping on that side and do not have sufficient ability to transfer power to the wheel above a certain (undefined) torque limit. IE, traction exceeds the amount of torque the system can handle.
