Discovery II SLS probem

Vehicle - 1999 Discovery II, Bosch 4.0 engine, ACE and SLS, 187,000km's (112,000 miles)
Couldn't see an answer to my problem in the SLS posts so thought I would ask.
Start truck, SLS light on dash flashes, compressor starts and rear suspension inflates, compressor shuts off but SLS light stays on permanently. If I back down the curb and stop, compressor kicks in and raises truck. If I stand on step (7 seater) at back, truck sinks, compressor kicks in and raises height. By the way, what is the correct standard height and where do you measure it?
When I bought the truck the previous owner (my nicest word to use) was driving with a broken rear sway bar link. Replaced both, air bags look good. Picked up a SLABS ECU from a guy breaking a 2000 with ACE, put it in and the SLS would not function at all so put the original back in. Haven't fiddled with the sensors yet but assumed if the suspension was raising level and stopping they are okay?
Talked to the dealership and they want $400 to try and diagnose it, they said it is harder on the older models. That didn't fill me with a lot of confidence so I figured I would ask the experts.

Worth getting a Nanocom or a Hawkeye code reader

You say that when you start the rear suspension inflates, by how much? The vehicle shouldn't sink when you stand on the rear step.
As MJI says, you ought to try to find a Nanocom or Hawkeye diagnostic code reader, but I would say that it really sounds like an airbag problem. They might have looked OK, but you won't necessarily see a leak just by looking.
Bags are easy enough to change, make sure you change both at the same time.
As to the normal ride height, I can't give you an actual figure right now, but the vehicle should "look level". Before you start getting into ride height sensors and all that goes with them, I'd make sure that the bags are right first.

brian47 said:

You say that when you start the rear suspension inflates, by how much? The vehicle shouldn't sink when you stand on the rear step.
As MJI says, you ought to try to find a Nanocom or Hawkeye diagnostic code reader, but I would say that it really sounds like an airbag problem. They might have looked OK, but you won't necessarily see a leak just by looking.
Bags are easy enough to change, make sure you change both at the same time.
As to the normal ride height, I can't give you an actual figure right now, but the vehicle should "look level". Before you start getting into ride height sensors and all that goes with them, I'd make sure that the bags are right first.

Click to expand...

Sitting over night (or when you get out) from the floor to the bottom of the wheel arch is 29.5", when started it raises to 30.75" (1.5" or about 38mm). When I stand on the step (just like someone using the occasional seats) it goes to 31.5" roughly, it's tough to do on your own because you lose a bit of height when you hop off the step by the time you get the tape set. I thought that was were the self leveling bit came in, if you had a trailer or more weight in the back?
But just taking the time to measure it points to a problem, I thought it was lowering then coming back to standard height but it appears to go higher.....hmm? Taking it to my buddies shop in 30 minutes to do the soap test, I'll let you know. As for 'looking level', always looks like it could do with being higher a the back (or lower at the front I guess).
Thanks for the responses.

MJI said:

Worth getting a Nanocom or a Hawkeye code reader

Click to expand...

Been trying to avoid that but you may well be right, I could almost buy one for what the dealer wanted just to look at it.

Canadian Phil said:

Sitting over night (or when you get out) from the floor to the bottom of the wheel arch is 29.5", when started it raises to 30.75" (1.5" or about 38mm). When I stand on the step (just like someone using the occasional seats) it goes to 31.5" roughly, it's tough to do on your own because you lose a bit of height when you hop off the step by the time you get the tape set. I thought that was were the self leveling bit came in, if you had a trailer or more weight in the back?
But just taking the time to measure it points to a problem, I thought it was lowering then coming back to standard height but it appears to go higher.....hmm? Taking it to my buddies shop in 30 minutes to do the soap test, I'll let you know. As for 'looking level', always looks like it could do with being higher a the back (or lower at the front I guess).
Thanks for the responses.

Click to expand...

Did the soap test, no apparent leaks on either bag. I'm starting to lean toward sensors but it is level side to side so I would be surprised if both are wrong in the same way. I guess instead of buying a Hawkeye I could convert to coils if I can't find a solution to the dash light.

Canadian Phil said:

Been trying to avoid that but you may well be right, I could almost buy one for what the dealer wanted just to look at it.

Click to expand...

Mine has paid for itself.

Only thing which got my ABS sorted in 2014

Canadian Phil said:

Did the soap test, no apparent leaks on either bag. I'm starting to lean toward sensors but it is level side to side so I would be surprised if both are wrong in the same way. I guess instead of buying a Hawkeye I could convert to coils if I can't find a solution to the dash light.

Click to expand...

Need a Hawkeye for that as well.

Just get one or a Nanocom and fix it properly.

They are worth every penny

Don't go changing anything yet. Get the fault code read first and go from there. The best way to test air bags is to run the engine until the car has leveled out, switch off, shut all doors, open the tail door, jack up under the tow bar about 2 inch then remove the jack and shut the tail door. If the car now goes down too the bump stops you have a leaking air bag.
It doesn't sound like you have a leaking air bag though, I would expect a faulty height sensor, but get the codes read.
The suspension height is set with height blocks that fit on the axle.

Canadian Phil said:

Been trying to avoid that but you may well be right, I could almost buy one for what the dealer wanted just to look at it.

Click to expand...

That might be what you're thinking right now, but what will you do when the next fault appears and you have to go back to the dealer to have the codes read again?

owl said:

Don't go changing anything yet. Get the fault code read first and go from there. The best way to test air bags is to run the engine until the car has leveled out, switch off, shut all doors, open the tail door, jack up under the tow bar about 2 inch then remove the jack and shut the tail door. If the car now goes down too the bump stops you have a leaking air bag.
It doesn't sound like you have a leaking air bag though, I would expect a faulty height sensor, but get the codes read.
The suspension height is set with height blocks that fit on the axle.

Click to expand...

I think I might breakdown and get the codes read, probably a good idea, I know others have said the same. There is something counter-intuitive (that really means I don't understand it) about the system, it doesn't seem as if it should be that complicated.......... until you add a computer I guess. I like things I can fix with a spanner[old English word that translates roughly into wrench]