'Extra High Mode' AHC......so tell me this.........?

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flintknapper

flintknapper

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Reading about the AHC system (Automatic Height Control) and came across a description of when/how the 'Extra High Mode' is activated, since it is not driver select-able.

So....someone enlighten me. Just how does the vehicle KNOW you are 'stuck' or 'unstuck'?

IF wheel speed is monitored ( I have no idea).....I would think that a spinning tire would also 'fit the bill' and you might very well STILL be stuck. How exactly does this work?

Just curious.

Extra High Mode.webp
 
Leandro said:
But I believe my manual says that it activates when it senses rough terrain, I suspect sensing the pressure and height changes.
Click to expand...

NM, I checked my manual and says the same thing as yours. I don't know where I got the rough terrain thing...
 
Two things

1) depending on how you read the paragraph, it could automatically activate when the vehicle is placed in 4L when in high mode already.

2) when placed in 4L and in high mode, it could potentially utilize the speed sensors and tell if the truck has met some specific parameters and will raise the truck to extra high when the parameters are hit.
Aka 2 weels spinning X amount of speed while others are not turning or going a very slow rate.
 
I experienced this Extra High mode once. My front end was dead on stuck in a thick mud hole and the center part of the truck was high centered.
The rear was having no traction and the rear wheels spinning, the truck moved all the AHC fluid to the rear shocks making the rear end really high and the front end looked like L mode.
I thought a sensor was screwed but after 30 seconds of driving it leveled itself out.
 
That's very interesting. I always thought that extra high mode = high mode when in 4 Low.
 
My guess is, it works the same way traction control works.... it senses a difference in wheel speed between 2 or more wheels. That coupled with the fact it monitors suspension height. No traction + high suspension height = High Centered. Commence extra lift!
 
Leandro said:
maybe there's a hidden microphone that hears you bitching....
Click to expand...

^^^^^ Until we know for sure......I'm going with this one. ;)
 
So in addition to the secret hidden microphone .....there’s a connection between the ABS/VSC/TRK ECU (at least for my ‘03) that signals the AHC ECU to kick up to the extra high mode when you get a TRK event + in low range + H height - pretty much like @hoser said except it’s the ABS/VSC/TRK ECU telling the AHC ECU to act, and not the dumb little AHC ECU working it out itself. As far as wheel speeds go, only the fronts are input to the AHC ECU, the rears aren’t.

0463B5DD-88FB-4782-824A-89441016D1BD.webp
 
Is that what is called "in-depth knowledge"...
 
PADDO said:
So in addition to the secret hidden microphone .....there’s a connection between the ABS/VSC/TRK ECU (at least for my ‘03) that signals the AHC ECU to kick up to the extra high mode when you get a TRK event + in low range + H height - pretty much like @hoser said except it’s the ABS/VSC/TRK ECU telling the AHC ECU to act, and not the dumb little AHC ECU working it out itself. As far as wheel speeds go, only the fronts are input to the AHC ECU, the rears aren’t.

View attachment 1615249
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Thanks for posting this. I’m having trouble finding this in the owners manual.
 
Thanks for the info that clears up my confusion. I was on a rough trail a while back and activated ATRAC a few times. After coming off of the trail my truck looked super high, higher than I've ever seen before. Must have put itself into Extra High Mode (love that name). Just to note, it never lowered itself back down to Regular High Mode either til I shifted out of low range and got back on the road.

GHVWznl.jpg


PrjGrq7.jpg
 
J1000 said:
Thanks for the info that clears up my confusion. I was on a rough trail a while back and activated ATRAC a few times. After coming off of the trail my truck looked super high, higher than I've ever seen before. Must have put itself into Extra High Mode (love that name). Just to note, it never lowered itself back down to Regular High Mode either til I shifted out of low range and got back on the road.

GHVWznl.jpg


PrjGrq7.jpg
Click to expand...
What kind of sliders are those?
 
Seems like this thread is pretty dead but i would like to just put out there that on my 2007 landcuiser i have measuered a 2" raise from n to hi and the rare amoout of time that i have encountered extra hi mode it has gone up 4 inches from n height. Also my front didnt drop, front and rear lifted 4" from n mode. To further add, no wheel spin was expierenced in this mode neither was the locker on, or the transfer case being in low. shortly after re modeling our house we had a dirt mount that was about 4 feet high and 6 feet horozantly to the crest, so nothing crazy but it seemed like thats all it took. The lc was quite tucked but just on the rear ( presuming becuse of the IFS) but we did also start in high mode. Another point is that during a snow recovery we got the lc high centered and all 4 wheels were spinning freely, even after trying to go to L mode on the ahc to compact the snow and then going to hi all wheels were still spining, so i dont know if it just wasnt recognzing that it was stuck but it just sat there like the fatest stuck pig.
 
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