Disco 2 fault finding - dead air suspension

hi all,

it's been a fair while since I've posted on here - the disco has been running smoothly which was nice! But over the weekend the curse of the air suspension has kicked in and the air appears to be dead.

I'll add some detail to that! there are no faults showing for the air (the 3-amigo's are on but that's due to a fault wheel bearing/sensor which I'm replacing next weekend), and my Nanocom shows no faults other than the sensor for the ABS/speed.

Air compressor doesn't appear to run (ride height adjust does nothing) and the test/adjust options on the Nanocom appear to process ok on the device but there is no audible sound from the compressor or movement from the rear end..

Fuse in the passenger compartment is ok (have swapped it just in case but no change)

So hoping that someone can help with where to look next - i'm a bit stumped (not for the first time!)

Air bags were replaced (dunop/new) about 24 months ago and other than a fair few "upgrades" nothing affecting the air other than a 2" riser block under each back to level off with the front spring lift....

all/any suggestions welcome!

Hi. Check fusible link FL9 in engine bay fusebox, if it's OK remove relay R5 and make a bridge across the perpendicular cavities in the fusebox for a second(there is the relay's contact), if the compressor doesnt kick in means it's dead(or a problem on that particular circuit, not so common but possible). If the compressor kicks in with the bridge put relay R3(headlamp wash) there and see then. According to the results we'll speak again

sierrafery said:

Hi. Check fusible link FL9 in engine bay fusebox, if it's OK remove relay R5 and make a bridge across the perpendicular cavities in the fusebox for a second(there is the relay's contact), if the compressor doesnt kick in means it's dead(or a problem on that particular circuit, not so common but possible). If the compressor kicks in with the bridge put relay R3(headlamp wash) there and see then. According to the results we'll speak again

Click to expand...

thanks @sierrafery - will check this evening and update accordingly

hi @sierrafery - have tried the above and no joy unfortunately so assuming the compressor is dead! I think I may be going down the route of springs on the back now as I need it working (to tow my boat) and from a bit of googling the cost of a (decent working) compressor is going to be prohibitive

if you are not determined to downgrade it to coils you should make sure that the compressor is dead not a wiring issue by measuring for voltage in the compressor's plug with that bridge instead the relay, if no voltage in the plug can be as simple as a bad contact at the fusebox or in the black two pin connector with the compressor's feed near it(C0376)

sierrafery said:

if you are not determined to downgrade it to coils you should make sure that the compressor is dead not a wiring issue by measuring for voltage in the compressor's plug with that bridge instead the relay, if no voltage in the plug can be as simple as a bad contact at the fusebox or in the black two pin connector with the compressor's feed near it(C0376)

Click to expand...

Thank you. Will attempt that this weekend

Towing. Keep air

similar problem ... both sides flat... checked fuse, relay and compressor... all ok.. had new bags about 4-6 years ago.
ran compressor for several minutes using a bridge across the relay socket... didnt lift up at all.
I think I have 2 problems, 1) the compressor doesn't come on without bypassing the relay, 2) when it is on the bags don't inflate.
I have a 1.8 ton caravan... and I've ordered the spring conversion kit... as I'm pretty sure it will be hassle free and wont let me down. (pun intentional)

As you'll convert it to springs maybe it's not relevant for you but maybe is usefull for others to know that you can't expect the bags to be inflated if you simply bridge the compressor relay cos the air supply valves are normally closed so to let air into the bags both valves must be energised at the same time

Well you certainly know your stuff... Thanks for the extra info. When I read this I did recall that when I bridged the relay the ignition and engine were off. So I've done it again with the engine on, (and all doors closed obviously)... and the bags have inflated. Yippee... So now we can use the car again - the kids will be pleased.
Maybe I wont fit the springs when they arrive but keep them as a back up.
To recap - the compressor works and the relay works. The problem seems to be that some element of the control system didn't send a signal to the relay to tell it to switch on.
I'm only guessing - but it seems unlikely that both ride height sensors would fail at the same time. The only other thing surely is the ECU - which also seems very unlikely as if it were to fail surly it would fail completely rather than partially.
So what could be the problem? Any further input you can offer would be gratefully received.
The suspension only went down the other evening when I had six adults in the car. Its possible the problem has been there for ages and I only noticed it because of this.
I'm going to pressure wash the underside, I've not done it for a few years. I've inspected the ride height sensors and although covered in muck they don't look like they could get stuck... but I'm sure a good clean wont hurt.
Thanks for your help. M

You need to plug in a hawkeye or similar to make sure that there is no "compressor duty cycle exceeded" fault code stored in the SLABS ECU cos if there is a leak the compressor works too hard to compensate for it and the ECU protects it with this default and the system will come to life only when that code is erased. To make sure it's not a leak disconnect the battery over night if you can and if it drops this way there is certainly a leak. 4-6 years can be enough for the bags to get "tired" depending on how and where the vehicle was used especially if they are aftermarket bags not genuine. This system is not very complicated once you can troubleshoot it properly and it's a big gain when towing