AHC & Being stuck?

[dinibili]

The Aust manual in its explaination for Extra high mode says this:
"If the vehicle becomes stuck, the vehicle height rises automatically about 70mm higher than normal mode. This mode changes automatically to High mode when:
1. The vehicle is no longer stuck,
2. When the four wheel drive control lever is in another position besides L.

Question. How does the vehicle know it is stuck. Wheel spin. Not likely. Vehicle being bridged. Doubt it. The Toyota dealer had not have a clue. He rang Toyota Technical. That bloke dribbled on a bit but did not know.

Any body out there have a clue?

 

[hkeller]

I would think it would be wheel spin. The VSC computer (which I think is tied to the AHC computer) senses wheelspin. As such, it is not much of a leap to think that, when the computer sense wheelspin for some defined period of time while the vehicle is in low, it interprets a stuck situation and raises to the suspension to extra high. It is probably a comarison of one or two wheel speed rates against those of the other wheels. If two wheels are spining at 20 mph and the other two are not, chances are you are stuck, or something really bad is about to happen.

You think?

 

[hoser]

The extra-high mode was also available with non-VSC (pre '02) 100's but there are the ABS sensors in all 100's.

 

[hkeller]

Huh, our 2000 LX has VSC. Its in the manual and has the lights on the dash. I hit a huge puddle doing about 65 around a corner one time and it saved my butt. It was loud as hell, sounded like somebody was beating on the wheels with a sledge hammer, but it worked.

 

[hoser]

Sorry, I meant to say "Pre 2000" rather than pre '02. My point was non-VSC LX's have extra high mode as well but no VSC.

 

[hkeller]

Gotcha, Hoser. The more I think about it, what else could it sense but differentiating wheel spin. Its an interesting question.

 

[Jim_Chow]

IIRC, the US owner's manual says it senses difficult terrain and automatically lifts it extra-high. I was thinking it might sense the amount of compression at each wheel and deduce that the terrain was very uneven.

 

[e9999]

well, remember that the computers know the speed of the vehicle, so it is not moving and the engine is chugging or wheel spinning, it must be stuck...

 

[dinibili]

However, if the TRC is doing its stuff no wheel should be spinning? Also I would have thought a spinning wheel does not indicate being stuck, just a spinning wheel. And if I have a spinning wheel do I need the vehicle raised? Probably not

A mystery?

Donald

 

[FinallyGotOne!]

oh boy, this could go on and on...the only way the vehicle can tell if it is moving is if the wheels are spinning....so if wheels are spinning, it can't know its not moving! Unless, of course, one wheel isn't spinning. Maybe that's the answer! But one of the times you most need "extra high" mode is when all four wheels are spinning and you are grounded on a rock or stump...

 

[dinibili]

Exactly!
As I said Toyota Technical did not have a clue. He just dribbled on and did a circle.
A Mystery!

Donald

 

[100 TD]

A very rare situation to have all 4 wheels spinning at the same time at the same speed, unless driving along of course, as with the CDL locked you get drive to front and rear although to have both fronts spinning the same speed they would have to be in the air, due to differential action, and both the rears would have to both be spinning the same speed as well, and they don't have a LSD( IIRC in dinibilis case), so it would be very rare(although possible), so since there is a speed sensor on each wheel sending an input to the ECU's and CDL input, I expect as mentioned before, the ECU sees a difference in wheel speeds by a certain amount over a certain time, and sees CDL locked or low range selected etc etc. The ECU also senses the throttle position, transmission gear selection, engine speed, fuel metering, etc, so there are plenty of input variables it can use to detect the situation.

 

[uHu]

IIRC, the US owner's manual says it senses difficult terrain and automatically lifts it extra-high. I was thinking it might sense the amount of compression at each wheel and deduce that the terrain was very uneven.

I agree.
Remember, it IS the AHC model we are discussing. There's a height sensor at each front wheel, and one for the rear axle. The AHC system can easily detect difficult terrain, i.e. different articulation of the different wheels' suspension.

 

[100 TD]

Certainly for the US model, it senses difficult terrain and shifts to extra high. But the original question for the Australian model from first post is that it senses when it is "Stuck". Difference in height of suspension does not signify a vehicle is "Stuck". Other inputs such as wheel speed I expect may come into play. The "difficult terrain" as mentioned in the US terminology, may well mean a combination of different wheel heights, Low range selected etc, as well as wheel speed and other inputs etc., coming to the same to the same conclusion that the vehicle is in "difficult terrain" or "stuck". Somewhere in someones FSM should be an explanation of the conditions that tell the AHC to go to extra high mode.
EDIT: If these conditions can be found out, all those with AHC may be able to install a switch or some electronic trickery to tell the AHC to go to extra high and utilise this as an advantage, or is it manually selectable as well?

 

[alaskacruiser]

What kind of lift does AHC give you guys in "extra high" mode? Is the lift the same in the front and rear?

 

[Bloodhound]

Your stuck

I personally think the computer is more in tune with monitoring speech patterns or words used within the cabin.
Plus signals to the computer from the spinster muscle sensors within the driver and passenger seats.
Not to mention the GPS is standing still but the Cruiser is moving 50mph, don’t ya think;p

 

[dinibili]

What kind of lift does AHC give you guys in "extra high" mode? Is the lift the same in the front and rear?

From the Book, Normal lift to High is 40mm in the front and 50mm in the rear. Extra High takes it to 70mm, so assume another 20mm front and back.

And Bloodhound, "Your Stuck" explains all the wires going into the drivers seat. Good to have a laugh first thing in the morning!

Donald