How To: LX570 AHC Disable, 20 MPH H Override (2 Viewers)

[TN LX570]

This solution stems from all the knowledge that was contributed in @turbo8's thread.

With a couple of simple switches you can disable the AHC (essentially locking the truck in whatever height you desire)

This will allow you to drive in H over the 20 mph restriction. To me the benefit is trails or roads where you're running 30 mph or so, and then slowing back down through a obstacle again raising the truck back up.

This is simply pressurizing (or depressurizing the system if you want) and locking it there. Meaning it is disabling the AHC and suspension mode settings.

As noted in the other thread the ECU (I think its the network gateway ecu) can be reset and the display will update itself accordingly as if it was never AHC equipped.​

There are of course multiple ways this can be achieved, but this is simplest I've found without generating additional errors.

 

[tbisaacs]

Super cool! Glad to see that AHC isn’t so scary

 

[TeCKis300]

Interesting. I'll agree with you that I don't know how practical this actually is, but I'll catalog this in the interesting category. It does go to show that once the AHC ECU is taken out of the CAN BUS loop and the system is reset, that the rest of the car will default to assuming a non-active suspension system.

You did mention it, but without the AHC ECU in the loop, all active functions are lost. Including all active damping functions, secondary spring rates, roll resistance, brake dive, etc. That IMO is a bigger part of what the system offers than just height. For fire roads or baja running even, the utility of this is a bit dubious because the active functions are more useful than outright clearance.

One of the use cases of the system that's not well understood by most owners is the use of low-range. Low range sets up the overall vehicle and suspension for off-road. For anything even semi-technical, this is the mode to be in. More suspension travel, more compliant damping, clearance, throttle modulation, and likely cooler running engine and transmission.

It automatically sets up the suspension for 2" more clearance up to 25 mph, and 1" more up to 50mph. Above that, center of gravity and handling stability is more useful IMO. With AHC continuing to monitor and increasing or decreasing compression damping situationally.

If one wants to setup the suspension for higher speed running, AHC sensor adjustment is the answer. Even a mild 1" adjustment there now means 3" more clearance up to 25mph, 2" to 50mph, and 1" everywhere else. All while keeping all the active damping functions active. IMO suspension droop is just as important so this is where I have my car setup.

Go crazier - 1.75" sensor adjust. Now it's 3.75" to 25mph, 2.75" to 50mph, 1.75" everywhere else. Or almost 5 full inches when in auto-extra high mode on stucks.

Working with the AHC systems and leveraging all it has to offer is where the real benefit is in my mind. I won't be turning off the system anytime soon.

 

[TN LX570]

@TeCKis300 As an AHC fanboy, I don't disagree with any of your sentiment. This really begin as more of a "can it be done?" quest than one of necessity. The real "solution" to bypass the H speed limit would be to intercept the CAN bus signals that are causing it to lower back down, and inject an overriding signal that retains the height. I would presume the ACH ECU is polling for a VSS signal, but not sure. Then you can have your cake and eat it too.

We know from previous threads that removing all the ACH relay, ECU, fuses, etc, would disable the system. I was surprised that simply taking it off the CAN bus, would have that effect. I found the same to be true for the AFS ECU (which I don't see any reason to disable), again remove the CAN wires, and truck will act like it was never there. I guess this is Toyota maximizing parts, when the truck starts it polls the system to see what features it's equipped with?

 

[TeCKis300]

I've been looking into how the VSS system on the vehicle works as I agree that it might be a way to hack the system.

Interesting now that I'm on 35s and VSS reads about 13% low. In towing, I rely on the AHC system to lower at freeway speeds as this has the side effect of increasing hitch weight distribution bar tension - enhancing the overall stability of the rig at higher speeds. As the system reads low, the lowering happens at higher speeds, ~70mph. Rather than the previous 60mph. My preference would be the lower speed in this case.

This does the opposite effect hat AHC maintains higher posture through higher speeds though.

There does seem to be a speedo correction adapter on the market that could correct/change VSS.

 

[HGB]

How likely do you think it is to find a way to intercept the system? That would be really amazing to be able to adjust on the fly.

@TeCKis300 As an AHC fanboy, I don't disagree with any of your sentiment. This really begin as more of a "can it be done?" quest than one of necessity. The real "solution" to bypass the H speed limit would be to intercept the CAN bus signals that are causing it to lower back down, and inject an overriding signal that retains the height. I would presume the ACH ECU is polling for a VSS signal, but not sure. Then you can have your cake and eat it too.

We know from previous threads that removing all the ACH relay, ECU, fuses, etc, would disable the system. I was surprised that simply taking it off the CAN bus, would have that effect. I found the same to be true for the AFS ECU (which I don't see any reason to disable), again remove the CAN wires, and truck will act like it was never there. I guess this is Toyota maximizing parts, when the truck starts it polls the system to see what features it's equipped with?

 

[ramangain]

Seems as if a software mod is the best solution; comment out the appropriate code, ensure checkeum is ok, then overwrite. Easier said than done, but by far the cleanest solution.

 

[TN LX570]

How likely do you think it is to find a way to intercept the system? That would be really amazing to be able to adjust on the fly.

It is as simple as wiring in a switch on the CAN bus line and one on the network gateway power for an “on the fly” change. That’s how mine is currently setup.
However you’re still going to need to be stopped obviously when you reset the network gateway.
(You could put a switch going to the ahc pump relay, fuse, etc... but without breaking the CAN bus signal and resetting gateway ecu you’re dash will be in mode.)

Intercepting and modifying the CAN bus signal is not unreasonable. I have captured some logs and analyzed it some. Like many things it’s a question of it’s commercially viable for someone to bring a device to market. I will say contrary to my post above, I don’t think it’s as simple now as just modifying the VSS signals.

 

[HGB]

It is as simple as wiring in a switch on the CAN bus line and one on the network gateway power for an “on the fly” change. That’s how mine is currently setup.
However you’re still going to need to be stopped obviously when you reset the network gateway.
(You could put a switch going to the ahc pump relay, fuse, etc... but without breaking the CAN bus signal and resetting gateway ecu you’re dash will be in mode.)

Intercepting and modifying the CAN bus signal is not unreasonable. I have captured some logs and analyzed it some. Like many things it’s a question of it’s commercially viable for someone to bring a device to market. I will say contrary to my post above, I don’t think it’s as simple now as just modifying the VSS signals.

Hmm... how do you feel about this method shown in the video below? Essentially they put the vehicle in high, turn it off, remove the AHC fuse, and then drive away. If I’m OK with the lights on dash, does this affect any other systems? VSC etc? The only plus to this method would be eliminating the need to pull the panel behind the passenger seat.

 

[TN LX570]

Hmm... how do you feel about this method shown in the video below? Essentially they put the vehicle in high, turn it off, remove the AHC fuse, and then drive away. If I’m OK with the lights on dash, does this affect any other systems? VSC etc? The only plus to this method would be eliminating the need to pull the panel behind the passenger seat.

There are multiple points in the truck’s wiring where you could kill the power going to the AHC pump. If the system is pressurized it will stay that way without power, unless you physically open a valve.
You will have dash lights, I know AFS will not function properly, not sure about VSC or other systems.
By “removing” the ECU from the bus, and then restarting the gateway, the system seems to be no longer expecting to find an AHC ecu. Hence it being removed from the gauge cluster display.

 

[Mago]

It is as simple as wiring in a switch on the CAN bus line and one on the network gateway power for an “on the fly” change. That’s how mine is currently setup.
However you’re still going to need to be stopped obviously when you reset the network gateway.
(You could put a switch going to the ahc pump relay, fuse, etc... but without breaking the CAN bus signal and resetting gateway ecu you’re dash will be in mode.)

Intercepting and modifying the CAN bus signal is not unreasonable. I have captured some logs and analyzed it some. Like many things it’s a question of it’s commercially viable for someone to bring a device to market. I will say contrary to my post above, I don’t think it’s as simple now as just modifying the VSS signals.

If I understand your 'on-the-fly' switch you have a double throw switch on the gateway power and the ahc bus. But can you really disconnect the gateway power while driving? Doesn't need some 'off' time to reset? Further details on this connection would be appreciated.

 

[Mago]

Interesting. I'll agree with you that I don't know how practical this actually is, but I'll catalog this in the interesting category. It does go to show that once the AHC ECU is taken out of the CAN BUS loop and the system is reset, that the rest of the car will default to assuming a non-active suspension system.

You did mention it, but without the AHC ECU in the loop, all active functions are lost. Including all active damping functions, secondary spring rates, roll resistance, brake dive, etc. That IMO is a bigger part of what the system offers than just height. For fire roads or baja running even, the utility of this is a bit dubious because the active functions are more useful than outright clearance.

One of the use cases of the system that's not well understood by most owners is the use of low-range. Low range sets up the overall vehicle and suspension for off-road. For anything even semi-technical, this is the mode to be in. More suspension travel, more compliant damping, clearance, throttle modulation, and likely cooler running engine and transmission.

It automatically sets up the suspension for 2" more clearance up to 25 mph, and 1" more up to 50mph. Above that, center of gravity and handling stability is more useful IMO. With AHC continuing to monitor and increasing or decreasing compression damping situationally.

If one wants to setup the suspension for higher speed running, AHC sensor adjustment is the answer. Even a mild 1" adjustment there now means 3" more clearance up to 25mph, 2" to 50mph, and 1" everywhere else. All while keeping all the active damping functions active. IMO suspension droop is just as important so this is where I have my car setup.

Go crazier - 1.75" sensor adjust. Now it's 3.75" to 25mph, 2.75" to 50mph, 1.75" everywhere else. Or almost 5 full inches when in auto-extra high mode on stucks.

Working with the AHC systems and leveraging all it has to offer is where the real benefit is in my mind. I won't be turning off the system anytime soon.

View attachment 2482794

I fully agree to the benefits of not disabling the system. However, when you are traversing the dunes when you need to maximize your approach and departure angles and need some speed attacking the dune. Every time you gain the speed required you are reducing those angles because the AHC will lower the truck. So a temporary 'lockdown' is required.

 

[Mago]

Sorry for this meaningless entry, couldn't insert the video and couldn't delete.