Rear Suspension Losing Air

[pax]

I have a stock 2008 GX470. I can set the air suspension at any height and it will stay and not droop at all even after days. Bust as soon as I drive it, within a mile I am in the bump stops. At stop signs I can raise back up. I sprayed everything I can see with soapy water and can’t see any bubbles. Any thoughts where else to look for the leak?

 

[HomersCanyonero]

First, it won’t stay in hi when you are driving over say 25 mph. It goes back to normal height at some set speed.

Second, sounds like your height sensors might be bad. Are they rusted?

I know I tricked mine by lowering them with nuts and washers, so that I would get a 1” lift in the rear.

 

[pax]

First, it won’t stay in hi when you are driving over say 25 mph. It goes back to normal height at some set speed.

Second, sounds like your height sensors might be bad. Are they rusted?

I know I tricked mine by lowering them with nuts and washers, so that I would get a 1” lift in the rea

 

[pax]

When I start the car before driving, the height will say normal and never changes as it begins to sag. Before I start driving I have space between the bump stop and the axle. After a mile, I am riding hard on the bump stop. If I go low then high and back to normal, it goes back to the original height with an appropriate gap. Techstream shows the sensors responding to the height changes in unison so I would think the sensors are ok. Techstream also shows no codes.

When I bought the car, it had new shocks and sensors. I am guessing they had this problem and gave up after the parts cannon. The air springs look original, but I sprayed every possible angle and get no bubbles. Is there a solenoid that could be leaking air as I drive? Wouldn't the height automatically adjust, or does it need to wait until under 20mph like you have to wait to adjust the height while driving?

I want to keep the air ride as I tow a small boat and it would be great to not have to worry about sag when loaded.

 

[white_lx]

When parked, the active height control is inactive. However, the system is still pressurized and if your vehicle stays up when parked for days, there is no air leak.

Once you start driving, the height control ECU monitors the sensors and bleeds air if considers the ride height too low and runs the compressor when it thinks the ride height is too low. It is possible that your sensors are not set correctly or for some reason the values change when you start driving. It seems that the height control ECU bleeds off the air in the bags, unless there is a leak only while driving (very unlikely).

Did you observe the L&R height sensors while driving? And what are you seeing in Techstream for a 'normal' ride height and what are the values for a 'low' ride height? Is there a large difference between L&R? My readings: HI ~ 1.5 inch, N ~ 0.0 inch, L ~ -0.7 inch (negative).

[edit] One other method to differentiate between a leak and intentional bleed of the bags is to switch off the height control before driving and see if the suspension will lower with AHC off.

 

[Rednexus]

You could also have dry rot/micro cracks in the bags that sometimes open up due to jostling (causing a leak) and close up (no leak). That's how my bags were when I pulled them (intermittent leak). They looked OK from under the rig, but upon removal they had hundreds of very small cracks in them.

 

[white_lx]

You could also have dry rot/micro cracks in the bags that sometimes open up due to jostling (causing a leak) and close up (no leak). That's how my bags were when I pulled them (intermittent leak). They looked OK from under the rig, but upon removal they had hundreds of very small cracks in them.

Telltale sign would be the compressor coming on in that first mile of driving. If it is trying to make up for lost air, it would be a leak (or combination of many tiny leaks). If it is not coming on, it would be the result of the AHC ecu intentionally bleeding the air.

 

[pax]

When parked, the active height control is inactive. However, the system is still pressurized and if your vehicle stays up when parked for days, there is no air leak.

Once you start driving, the height control ECU monitors the sensors and bleeds air if considers the ride height too low and runs the compressor when it thinks the ride height is too low. It is possible that your sensors are not set correctly or for some reason the values change when you start driving. It seems that the height control ECU bleeds off the air in the bags, unless there is a leak only while driving (very unlikely).

Did you observe the L&R height sensors while driving? And what are you seeing in Techstream for a 'normal' ride height and what are the values for a 'low' ride height? Is there a large difference between L&R? My readings: HI ~ 1.5 inch, N ~ 0.0 inch, L ~ -0.7 inch (negative).

[edit] One other method to differentiate between a leak and intentional bleed of the bags is to switch off the height control before driving and see if the suspension will lower with AHC off.

I honestly didn't pay attention to the numbers, only that they are changing. I am going to check them tonight. Should they always match each other?

I am also going to try the off setting while verifying the numbers.

 

[pax]

Telltale sign would be the compressor coming on in that first mile of driving. If it is trying to make up for lost air, it would be a leak (or combination of many tiny leaks). If it is not coming on, it would be the result of the AHC ecu intentionally bleeding the air.

Interesting. I don't hear the compressor kick on while driving. I wonder if that points more towards an ECU issue?

 

[pax]

Problem solved. The sensors were not in sync. The readings were 2 inches off. Once I adjusted them to within .1 inch on level ground, everything leveled and stayed level. My guess is the dramatic reading difference confused the computer and it defaulted to deflate to avoid popping the bags.

Thanks for all the advice guys. You all got me looking in the right areas to find the problem.