[Nyevol]

In Suspension Control System module in the Service Manual there are literally 50 pages of diagnosis of different scenarios and dozens of codes that could indicate what the problem is. You need to start there. You will need a dedicated Nissan OBDII reader that has ability to access all vehicle systems. Go to “E-SUS” module and read codes.

If you have an older compressor that runs in environment with road salt and moisture (i.e Rust Belt) the compressor is a common culprit of all problems. It develops internal leaks. They can be small but if you load the vehicle up it needs to work extra hard and if it runs for 180 sec and cannot achieve proper height it will shut down completely until you turn the ignition off. This resets the malfunction condition (but the code should stay in the history) and it could be one of the scenarios. This code is C1808 but again there are many others for many other scenarios so you need to know what the code is.

If you have an old compressor, and don’t want to get the dedicated reader ($300+) I would just buy a new compressor and see if this fixes it. In 9 out of 10 times it will as this is the weakest link in the whole air lift system. Shocks, airlines and height sensor failures are less common.

Pete. Thank you very much.

 

[Wifeysride03]

Pete32500, thanks for the write up! Project was completed today and the rear end is back to normal.

 

[Pete32500]

I am glad to hear it all went well! You saved ~$600 but what's way more important is satisfaction of a well done project. That is priceless .

 

[Wifeysride03]

Not sure if you able to help me but now the rear suspension is too high! Every time I start the car I hear the compressor running for 5 minutes. Not sure if there is something else I should check? Any suggestions would be appreciated

 

[Pete32500]

Please provide more information... How high is it? How much higher than nominal 35"? Compressor running for 5 minutes is not good. Suspension Control System should shut down the compressor after 180 sec running time. To achieve proper level it should take about one minute or less. Does the vehicle sags down after it sits overnight? Or it sits high and compressor runs for 5 min anyway? There is a way to set up the vehicle height but I am puzzled why this would be required. The compressor should get a signal to shut down once proper height is achieved.

 

[Wifeysride03]

Car in the garage, measured it was 36 1/2, started her up the compressor came on for 2 minutes and when the compressor turned off the car measured 37 and 1/4. That is from the ground the the fender.

 

[Wifeysride03]

Here are some pics

 

[Pete32500]

This is very unusual. Changing the compressor does not require any adjustment to vehicle height. The only reason to adjust the vehicle height setting is if the height sensor is replaced or removed and re-installed or if the entire air levelizer control module is replaced. See the service manual note:

"Air levelizer control module enables precise control, by acquiring memorized standard vehicle height and signal (vehicle height) from vehicle height sensor. For this reason, always set standard vehicle height after performing the following operations: • Removal and installation or replacement of vehicle height sensor • Replacement of air levelizer control module"

What is unusual is that the vehicle starts high and compressor keeps pumping to get even higher. Have you always owned this vehicle, especially when the compressor was operational and you know the height was properly set? Or is it possible someone messed with the height sensor, or it was bumped and you didn't know it was set wrong because the compressor was not working before? This is really puzzling...

Anyway, it would be good to see what codes you are getting, if any. This would narrow down diagnostics to specific section as it would point you to understand where the problem is. Either height sensor, compressor, control unit and so on. For this you will need a dedicated nissan diagnostic tool (such as Foxwell NT710 with Nissan software) that can connect to the suspension module. Here are the codes:

If this is the case that the vehicle height is properly set but the compressor keeps pumping over the reference height you would likely get this code.

Below is diagnosis procedure:

Which in my opinion the most likely scenario is the height sensor problem (bumped, damaged, moved, improperly installed, not set correctly) and if no obvious findings then set the standard vehicle height.

You can reset and set the vehicle height with Nissan CONSULT. I am not sure if Foxwell can set it up since I never need to changed that. I do know Foxwell can activate the compressor or exhaust solenoid to raise or lower the vehicle so my guess is it has that action.

If you don't have the tool that allows you to do this I think the trip to the dealer will be needed...unfortunately...

 

[Pete32500]

Take a look at post #4 of this thread. This is how the sensor should look like. Mounting bolts should be centered in sensor slots and there should be some threads visible of adjusting rod. This is how the factory would install it.

 

[Pete32500]

And of course I wouln't be myself if I didnt check...Foxwell NT710 does have a functionality to set the Standard Height Level. It is in E-SUS module under Special Functions... knowing is better than wondering....

 

[Wifeysride03]

Thanks Pete, I made an appointment with the dealer and the service advisor stated the suspension needs to be recalibrated. I have an appointment for Thurs and will keep you updated

 

[Wifeysride03]

Hey Pete, just wanted to give you an update. Unfortunately my wife was fed up with the vehicle from not starting at the first try a couple of times to the suspension. She traded in her vehicle. Sorry I was unable to come up with the problem. It’s still a great car but she just wanted to upgrade. Thanks again for your help.

 

[Nyevol]

Pete. Thank you very much.

Pete,

Thanks again! Another very happy QX80 owner. No more sagging. Order the compressor from ebay and installed it in less than an hour and a half thanks to your write up. I was lucky. I do not live in the rust belt so all the bolts came off with ease.

 

[Pete32500]

Pete,
Thanks again! Another very happy QX80 owner. No more sagging. Order the compressor from ebay and installed it in less than an hour and a half thanks to your write up. I was lucky. I do not live in the rust belt so all the bolts came off with ease.

Excellent! 1 1/2 hr is really good. I am glad my write up was useful. This is not difficult and yet you saved quite a bit of money over to what dealer charges.

 

[rwehling1008]

Does anybody know if the air compressor will run while driving? The Infiniti mechanic said it does not. Since weird.
Also I have put air bags in the rear coil spring on our QX56 and QX80 which helps when towing.

 

[Pete32500]

This doesn't make any sense and would defeat the purpose of the self leveling system. Below is the Air Levelizer Control System description.

"Based on the signal from the vehicle height sensor, the air levelizer control module operates the air compressor (exhaust solenoid) and controls vehicle height so that it remains at a constant height. This operation occurs if vehicle height of vehicle rear is judged to be 15 mm (0.59 in) or more or 15 mm (0.59 in) or less than standard vehicle height, continuously for 30 seconds, when engine is started."

In other words, once you start the "engine" the system will analyze the vehicle height for 30 sec before it activates the compressor or exhaust solenoid and adjusts the height if needed. In the description it says nothing that the vehicle needs to be stationary. Imagine the scenario that you load the vehicle, hook up a trailer, start the engine and start driving. If the system only operates when the vehicle is stationary it would rarely work, which makes no sense at all.

Interestingly, the system gets input from ABS actuator and electronic unit for vehicle speed but this is only used for detection of height sensor performance. It looks for a condition of no change in height (using the sensor voltage) for 100 hours of driving over 2km/hour . If this occurs it will flag a code C1806 indicating height sensor malfunction.

You can simply test it. Load the vehicle, start the engine, wait for the compressor to kick in and start driving...and you will hear it running until height is achieved. Mine would kick in all the time, while driving, and this is how I knew it started getting bad. It shouldn't really kick in when driving that often as this indicates a leak in the system.

 

[rwehling1008]

Agreed, I think it would run while driving. When I was a towing a camper, I would get gas, start the car and the compressor would kick in to level the vehicle.
When I stopped again for gas, the car was sagging.
The dealership checked and no codes were logged indicating issues.

 

[Pete32500]

I would guess the compressor is wearing out and it developed small internal leak(s). When you load the vehicle with a heavy load/trailer it has to build up even higher pressure to level the vehicle and, due to these potential leaks, it cannot achieve the proper height within 120 seconds. Then it shuts down and will not activate anymore. As you continue driving the compressor continue leaking, as the heavy load keeps "pushing" on the air system and you keep losing the pressure until the rear just sits on the coil springs, without any assist from the air shocks. The compressor will not re-activate until you turn off the vehicle and restart it. I am not sure if the E-SUS module codes are stored. This could be the reason the dealership could not read the codes. If I had this situation I would hook up the Nissan code reader and monitor as I drive with the trailer. If your compressor is old I would start with replacing it. This is the most common culprit of all rear suspension leveling issues.

 

[rwehling1008]

Thanks for the feedback. On our 2011 QX56 we had similar issues and the dealer was able to local the codes to determine what to replace.

So the compressor will only run 120 seconds and then stops whether or not the correct is achieved?

Again, thanks for the feedback.

 

[Pete32500]

There are a few conditions in which the air levelizer control module will go into fail-safe mode and will shut down the compressor. For instance If you "significantly" overload the vehicle, the compressor runs for 120 sec and is unable to achieve standard vehicle height position. Or if there is a leak, which it would result in pretty much the same condition. There is also cumulative operating time of the air compressor of no more than 180 seconds in one ignition cycle. Meaning that if you start driving, compressor runs for 90 seconds to set the height, but there is a leak and compressor needs to pump more air 3 more times for 30 sec, then it will shut down and will no longer restart until you turn the vehicle off and on.