How to diagnose air ride compressor

[ukrkoz]

2011 QX56 with 151 000 miles
Air/hydraulic ride in the rear.
Compressor and height sensors replaced 1.5 yr ago,

All was good for over a year.

Rear airbags stayed inflated as they should.

Last Saturday, I installed Firestone in spring air bags. Made sure not to damage anything along the installation.

Pumped them up and it all went well.

Yesterday, I noticed that rear is lower than front. Measured, indeed, was about half inch lower.

This is what I found:

1. one Firestone airbag is slow leaking air at the air line connector. Between the brass connector and bag itself, not from the air line to connector.

2. OEM air bags are completely deflated. They DO NOT leak air at all.

I put system in Aux mode and waited. Compressor will not come up.

I connected scanner and went into functions. Found Compressor in E-SUS section and it started from scanner without problem.

Apparently, compressor works fine.

Height sensors were replaced during the original replacement 1.5 year back.

What can prevent compressor from kicking in then?

Problem is, until I receive replacement Firestone air bag, I either have to let rear to sag completely or, pump Firestone bags every day, pretty much.

Could it be caused by Firestone bags not allowing vehicle to lower itself enough for the sensor to trip compressor?

It drives much better with both OEM and Firestone bags inflated.

[VStar650CL]

The levelizer system is supposed to operate anytime the rear height is more than +/- 15mm (about 0.6") from standard. If you have HBMC (hydraulic suspension) then it's a different animal, but I'm assuming you don't. The "standard height" is a memory setting captured by the controller using work support, so if you changed the compressor and sensor without initializing it, that could explain it not leveling correctly. It may have been a little off all along, but the one working Firestone bag is now holding it up enough to make the discrepancy noticeable. See SC-67 here:
https://www.nicoclub.com/service-manual ... %2FSCS.pdf

[ukrkoz]

Thank you.
I'll remove sensor tomorrow and jock it like as if rear is sagged. If comp comes up, I'll have to initialize sensors, I have that on scanner. Will work or not, I'll find out.
I'm thinking, maybe I simply should adjust sensor arm length. It's adjustable. OEM bags worked just fine until the F-stone bags were added.

[VStar650CL]

That's true, it's all dependent on the arm. Garage guys usually just mess with the adjustment until it works right, and honestly, I don't see any harm in doing it that way.

[ukrkoz]

Didn't have chance to get to the sensor yet, maybe in few hours but here's what I found:
C1805 code, Height control sensor down.
It showed yesterday, I cleared them all, took her for a drive this am (rear was still 3/4 inch up vs front, so OEM bags hold) - and that code returned.
I know, it's very simplistic, but the way I read it, it does say, that sensor reads CA position as lowered and no need to turn on comp, and then OEM bags slowly loose air, as they should.
Also, I did solenoid check, and I can hear it click, so no issue there.
I'm more and more leaning towards simply adjusting the arm on sensor to make it believe that suspension is slightly sagged. Error and trial, of course.
Does anyone know if there's pressure sensor in the bags, cutting it off preventing overinflation? Don't want to blow bags or burn comp, if I adjust it too much.
Oh, and I do have hydraulics. If it makes difference. Oil change is $852 plus tax dealer only, hence all this goofy stuff with Firestone bags.

[ukrkoz]

OK, not to overwork myself - I had hard labor 8 to 12 in property - I simply deflated Firestone airbags (FAB) and let rear to drop down to its normal height.
Keeping in mind that OEM bags were still inflated from yesterday's experiments.
Turned system on - comp will not kick in.
Maybe it's that stored code that prevents it, maybe height is at where it should be for sensors per OEM airbags.
I do need to do height adjustment procedure, but that takes lifting up the vehicle and I'm tired.
I'll do it next weekend.