So, my SLS is doing something weird. I recently got my Disco back from my mechanic after they were troubleshooting some wiring harness issues related to some sensors with the transmission. It drove great coming home. I parked it, (not my daily driver) and noticed a few days later that the left-rear air shock was completely flat. This has happened before and I just fire it up and it pumps right back up again. No big deal. Well, this time it didn't. The right-side seems low also, but it's not flat. After poking around a little I notice that I don't hear the compressor running. So, I try pressing the lift button. Nothing. The little dash light lights up while I'm pressing the button but goes out when I release it. I tried driving it 15-25MPH around my neighborhood to see if it would level out, but it didn't. I checked the 2 related fuses and they are fine. (checked with multi-meter).

I popped the relay out, and connected it to a 12V supply I have, and it clicked, and the contact side tested ok for continuity. This is what I think the problem is, but I'm not sure how to troubleshoot it, I have some theories, but they probably are based on a complete misunderstanding of how the system works.

The problem(I think): The relay is only seeing 4V when the key is on, or the engine is running. Which clearly is not enough juice to get the relay to click. No matter what I do, it just sits at 4V. I shorted the contact side of the relay and the compressor fires up and runs. No air is going into the bags though. I've sprayed windex on all the hoses and connectors (which were replaced under warranty about 6 years ago, along with the air bags and still look band new) and I don't see any leaks. I pulled the connector off the back of the fuse panel and tested the leads for voltage. Grounds have continuity to the frame and battery ground, and the lines you would expect to be 12V are 12V - Except 2. Those show 4V. One of them I'm pretty sure is the SLS, I'm not sure what the other one is though. Hopefully nothing I have (stability control?). The 2 pins that show 4V are right next to each other on the connector and one has a Orange/White wire going to it and the other has a smaller gauge solid brown wire.

I've been studying the WAVE manuals and it doesn't seem (or at least the one I found) to have a great functional description of the SLS system. What it FEELS like to me is that the SLABS ECU might control valves or something, and it doesn't know the compressor is running (when I manually turn it on) so it's not directing the air where it needs to go. If I get the correct voltage at the relay, I think the ECU would control the valves properly and I'll get air.

Anyway, I'm not a mechanic so I'm probably talking straight out of my boot here, but this is what I'm observing. The mechanics solution was to wire in an external switch to turn the compressor on/off. I THINK with my testing I've proven that THAT won't work.

So I guess the questing I need to answer is, Why is the coil side of the SLS relay only getting 4V?

Any suggesting on getting my 2003 Disco 2's left butt cheek off the ground would be great.

THanks,
Brian

 

if it was fine before maybe mechanic messed it up? Trace the harness they worked on.

 

X2.

If im reading this corrextly, you don't feel like taking it back, and you feel adventurous, here is your diagnostic flow.
Find the end point of the two wires that are providing 4v. Do a resistance test, end to end. You seem to be pretty handy with a multimeter, so this should be relatively easy. If it's reading anything higher than 0.2 ohms, you have a high resistance. If it read 0.2 ohms, you need to find where those wires are getting power from. If it's the slabs ecu, you may need to replace the ecu.

But I'm just a grease monkey... so I may be wrong.

 

Firstly have you tried reading the fault codes?

Has the compressor filter behind the drivers side rear light ever been cleaned?

Has the SLS compressor ever been changed/renewed or refurbed i.e new piston ring?

It sounds like an SLS sensor problem or leaking air bag suspension. Why were the air bags and lines replaced under warranty on a 12 year old D2? it's way past it's LR warranty.

Try cleaning the SLABS main plug and the SLS plugs into the sensors first. Spray them with electrical contact spray.

 

Yeah, that's what I figured. The mechanic made is clear that he has no interest in working on it. I don't have a whole lot of options where I live so I figured I'd see what I could do on my own before taking more drastic measures.

 

Thanks. I was looking for the end of that harness when I decided to post my issue here. I'm not sure where it goes. The WAVE manual says the SLABS ECU is under the driver side dash, so I assume it goes there. There's a WHOLE mess-a-wires in there but I didn't see that ECU. Maybe I need to pull that foam thing down. However, the bundle of wires ALSO seems to go to the main ECU which I could get to easily, but I didn't see the white/orange or brown wire I was looking for. Looks like I should probably get back to looking for the SLABS ECU. Thanks.

Brian

 

There are no dash error lights, so I assumed there would be no codes.


If it has, it wasn't by me. Didn't know that was there.

Not sure. I'd have to look at the old service records. It looks SUPER clean, practically brand new, so I'm thinking it was replaced with the warranty work that was done. Maybe not.



I agree with you on the sensor. I should try reseating those and maybe trying to clean them up a little. As for the warranty, I had an extended warranty on it through 100,000 miles or 10 years. at about 96,000 the rear suspension wouldn't hold air anymore, so I got it replaced JUST under the warranty. That was about 6 years ago.[/QUOTE]

Will do!

THanks!