Turning off air suspension when towing?

[ESnyder]

Questions about the adjustable suspension in our 2006.

When towing anything heavy, it goes into low mode. I don't like the ride height for this if on any kind of uneven terrain, and it puts the safety chains, etc. lower to the ground. There is an "OFF" button for the suspension, but it doesn't seem to actually turn it off.

Is there a way to set the air suspension at the mid level mode and just keep it there?

Thanks!

ES

 

[PADDO]

AHC dropping to Low is normal behavior for an overloaded system, and this will be exasperated if it's under maintained and way out of factory specs. The OFF button comes into play for things like hooking up trailers or putting on chains, actions where you don't want the system self adjusting height for safety reasons. If you turn the system OFF when stationary it will automatically turn itself back on as a function of vehicle speed. OFF at N it will turn back on above 50mph, OFF at L or H and it comes back on at a lower speed. Basically, its not designed for normal highway driving in the OFF mode or any mode other than N. If you regularly tow and its overloading the system you're probably a good candidate for air bags, something like Firestone 4124s or Air Lift 1000 series. But before you consider installing air bags I'd recommend you ensure you're up to date on your AHC maintenance - baseline the hydraulic fluid (it's not an air system like Range Rover) with new fluid and purge any entrapped air, check vehicle front and rear heights and measure your neutral pressures with Techstream to determine how much your torsion bars need adjusting and if you need new rear coils/spacers.

 

[ESnyder]

Good explanation and I suspected that the default engages under load. Would low fluid explain why the system self adjusts the height frequently up or down, seemingly at random?

 

[PADDO]

Self adjusting height to achieve level is the active part of Active Height Control, so yes it's normal for it to do small front or rear adjustments as the vehicles attitude changes when pulling up to a stop light, or passengers get out or starting after being parked for a while for example. If your fluid level is seriously low you will eventually draw in air and the pump won't be able to make pressure and the system will time out and turn off, so small height corrections aren't a symptom of low fluid. If your fluid level is at or above the MIN line on the reservoir you're ok.
Edit: above MIN whilst at Normal height on level ground

 

[TXLX100]

Good explanation and I suspected that the default engages under load. Would low fluid explain why the system self adjusts the height frequently up or down, seemingly at random?

No, but you'll want to ensure the fluid is at an acceptable level in the resevoir so that the system's pump can operate properly and not overflow the resevoir.

The system adjusts up or down automatically to maintain the height setting (low, neutral, high).

 

[TeCKis300]

AHC dropping to Low is normal behavior for an overloaded system, and this will be exasperated if it's under maintained and way out of factory specs. The OFF button comes into play for things like hooking up trailers or putting on chains, actions where you don't want the system self adjusting height for safety reasons. If you turn the system OFF when stationary it will automatically turn itself back on as a function of vehicle speed. OFF at N it will turn back on above 50mph, OFF at L or H and it comes back on at a lower speed. Basically, its not designed for normal highway driving in the OFF mode or any mode other than N. If you regularly tow and its overloading the system you're probably a good candidate for air bags, something like Firestone 4124s or Air Lift 1000 series. But before you consider installing air bags I'd recommend you ensure you're up to date on your AHC maintenance - baseline the hydraulic fluid (it's not an air system like Range Rover) with new fluid and purge any entrapped air, check vehicle front and rear heights and measure your neutral pressures with Techstream to determine how much your torsion bars need adjusting and if you need new rear coils/spacers.

Nailed it.

To the OP, 'L' mode is normal and expected for a the AHC system beyond its constant height weight threshold. Just like a normal suspension car would sag with too much weight...so does the AHC system, beyond a certain weight limit.

Like PADDO mentions, you may need to do some maintenance on the suspension. I have an '06 as well and I've added a 10mm spacer over the rear coils and increased the pre-load on the front torsion bars, as they're tired after so many years. The front AHC pressures are back in spec, but the rears are still slightly out of spec, which basically puts more of the weight load on the AHC system. This decreases the constant height threshold of the AHC system.

You'll probably want to add 20mm spacers to the rear or buy new coil springs to put everything back in spec. Or the quick and dirty (but flexible) fix would be airbags.

 

[deanfun]

Like PADDO mentions, you may need to do some maintenance on the suspension. I have an '06 as well and I've added a 10mm spacer over the rear coils and increased the pre-load on the front torsion bars, as they're tired after so many years. The front AHC pressures are back in spec, but the rears are still slightly out of spec, which basically puts more of the weight load on the AHC system. This decreases the constant height threshold of the AHC system.

You'll probably want to add 20mm spacers to the rear or buy new coil springs to put everything back in spec. Or the quick and dirty (but flexible) fix would be airbags.

Where'd you grab your 10mm spacer?

 

[PADDO]

10mm spacers don't really achieve that much of a pressure reduction, maybe 0.2 or 0.3MPa is my experience, not really worth the effort. Go for 30mm at least to make a tangible difference. At present I'm running 40mm on 6 year old coils for 6.1-6.2MPa. I'll install those 40mm spacers over new coils I've yet to install to get the rear pressure even closer to 5.6MPa. Of course it's important to know what your initial pressures are so you can target and fine tune for your preferred pressures.

 

[ESnyder]

Good info. spacers or new coils will get the back end back up in spec to counteract the sagging aged system. This would help the L setting not be quite so L.

All this against the open question about how much I should really be towing with my wife's daily driver

Thanks, MUD!

 

[nahtnoj]

Yeah, no one has asked yet how much weight.

I towed a ~3,000lb trailer last summer with no issue. Pretty sure my springs are on the tired end of the spectrum.

 

[PADDO]

Good info. spacers or new coils will get the back end back up in spec to counteract the sagging aged system. This would help the L setting not be quite so L.

All this against the open question about how much I should really be towing with my wife's daily driver

Thanks, MUD!

The vehicle is rated to tow 5000lbs with 500lb tongue weight maximum. It crosses into overloaded territory at 1260lbs of cargo and passengers (4x150lb people and 660lb cargo) so with three or four normal size passengers, junk for a week trip and 500lbs of tongue weight you're quickly pushing/exceeding the design limits for normal operation. Now these specs are based on a system that has neutral pressures in the design ranges, but we know static pressures go up as torsion bars and coils age and sag. Accordingly, a system that already has high static (neutral) pressure will exceed the maximum pressure thresholds, as measured by the system's pressure transducer (this is the transducer output that Techstream reads to populate the pressure fields in the AHC live data test) more readily when loaded causing the AHC ECU to prohibit leveling back to Normal height for example and command it to drop to Low. Bottom line is for maximum tongue weight and cargo capacity you need to keep neutral pressures at their design points, if you're neutral pressures are high then you sacrifice full load capacity.