We tackle Toyota Flagship's Active Height Control limitations

June 28, 2006
We tackle Toyota Flagship's Active Height Control limitations

We think Toyotas Flagship Sahara is too 'clever for its own good.

Our towing team have used various reliable Toyota Landcruisers for towing since 1992, but the latest addition to thecompany towing fleet, a current model Sahara, poses problems with its new Active Height Control (AHC).

As Toyota tends to introduce new systems in the Sahara (after the Lexus) and then add them to other models like GXL GoSeeAustralia thinks it is worth discussing the problems created by the Active Height Control system and the method GoSeeAustralia has devised to allow suitable set up of a Hayman Reese or similar towing systems.

The AHC causes problems with adjustment to our Hayman Reese hitch system and workarounds have been devised to get a workable outcome with this vehicle. GoSeeAustralia has approached Toyota via phone and email for some technical information but so far we have no response.

Editors note: If in the future we hear from Toyota we will adjust this feature as appropriate.

First we need to explain how the AHC works and its design according to whatwe can glean from Toyotas owner material. Our phone call to Toyota got us to the help desk and their information is unfortunately in error and contrary to the manual.

This table from the Landcruiser manual is an overview of what is intended with the AHC system

Older Hayman Reese tow hitch showing the height adjustment holes
Older Hayman Reese tow hitch showing the height adjustment holes
Low ModeNormal ModeHigh Mode
At Vehicle stoppage
Yes
Yes
Yes
Under 30Km/h
No
Yes
Yes
Over 30 Km/h
No
Yes
No

Toyota says that the vehicle cannot be raised if the load exceeds the following

Up to 4 occupants* plus 280 kg in normal mode

Up to 4 occupants* plus 150 kg in high mode

* Occupants average weight is 75 kg

Toyota says that - If the above load capacity is exceeded then the desired vehicle height may not be obtained even if the height select switch is pushed. And adds If the vehicle height cannot be raised in normal mode and the height control indicator indicates LO this is because the vehicle is loaded too heavily. Under these conditions, drive your vehicle with due care

The Toyota manual sets the following loading and towing capacities for the Sahara.

Max towing - 3500 kg

Max ball loading - 350 kg

Gross weight on vehicle should not exceed 3260kg

Kerb weight (from Toyota Website) 2675-2710kg

Therefore max overall vehicle load 550 585kg

The normal method of fitting the Hayman Reese system (simplified) is to -

1. Adjust ball to be same height as the caravan cup (with van levelled).

2. Hook up the van so normal ball load is on the vehicle.

3. Add the torsion bars and adjust up so that vehicle is level again. (GoSeeAustralia does this by measuring the height from under the guards to the ground on front and back wheels. We maintain the same differential after the caravan is hooked up which allows for the vehicle to be proportionally lower for the additional tow ball load.)

But here is the problem. If the vehicle with Active Height Control has its engine running it will immediately adjust the vehicle to level itself without the fitting of the torsion bars.

Secondly, depending on loading, it may go into the low mode (LO) which is about 5-6cm lower than normal height. Further, it appears that the way the Active Height Control adjusts to equalise the vehicle height is to not only raise the back but also lowers the front of the vehicle to match the rear.

So after trial and errorour suggested method of set up on our company Sahara with AHC is:

1. Adjust the tow ball to be same height as the caravan cup (with the caravan levelled).

2. Move the vehicle ready for attaching the caravan and switch off vehicle.

3. Hook up the van so normal ball load is on the vehicle.

4. Add the torsion bars and adjust up so that vehicle is level again.

5. Measure the height of the ball and start the vehicle.

6. Re-measure the ball height, if the ball has lowered turn off the vehicle disconnect the caravan and reset the height of the tow ball on the vehicle up by the difference lowered (on the GSA Sahara this was 5cm).

Loading up the torsion bars
Loading up the torsion bars

The rest is trial and error depending on the vehicle load and tow ball loading.

If the height changes with say fuel load because of the difference between empty and full as it passes through the sensors limit setting then the tow ball may need to be adjusted to split the difference.

This means a balance depending on the load and fuel use during a trip so as not to be at one extreme or the other.

To use the Sahara as an example on the differences in ball height with ball already set as per the GoSeeAustralia method described above

44.5cm unloaded

33cm with caravan hooked on but no torsion bars added

35.5cm bars added and loaded up

37cm after Sahara started

It should be noted that there is a 7.5cm difference in the height of the vehicle from start to finish.

A possible solution could be to add air bags that can be pumped up to take some of the load. This has not been tried but it seems to be a reasonable option for owners who constantly tow heavy loads.

Editor's Note also see:

Hayman Reese hitch fitted with dual cam sway controller
Hayman Reese hitch fitted with dual cam sway controller
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