My wife drives a 2005 XJ8 and she told me tonight that the Car Too Low light has been on for a few days. She said she can hear scraping a little from time to time.

We used to get an Air Systems Fault when the weather was real cold, but now the Car Too Low light is on constantly.

I'm not very familiar with air suspension. Can someone explain where the components are and where I should begin the search for the problem?

Thanks in advance.

 

First thing to check is the suspension COMPRESSOR RELAY.
I have replaced many relays and sent the customers on their way.
The contacts get burnt from the high load and constant cycling when the air springs get older and seep.

Could be a failed compressor or faulty sensors etc.

There might be fault codes logged in the suspension module?

bob

 

Thank you for your reply. It would be great if it was just a relay. The relay is R1 in the engine compartment fuse box. I'll check that out in the morning.

 

Is the car really low (because then it should not be really driveable)?
It seems that on some cars, if you have the red light with suspension too low signal, the compressor does not restart unless you erase the DTC. Even more, the compressor may not sart even when the engine is ignited with the car remaining in Park.
Not the case on mine where the compressor starts on Park when too low and may also sart when driving, even at very low speeds.
So listen to see what happens.
Then, either the compressor or one or your shocks may be on their way out.
Look at the varios threads on the issue

 

Hi RLB828,

I second paydase's concern that if the car is sitting so low that one or more tires are rubbing against the wheel arch liners, the car should not be driven until the problem is resolved.

Bob's recommendation to check the air compressor relay is a good first step. The fog lamp relay is R6 in the same Front Power Distribution Fuse Box where the air compressor relay is R1, so you can try swapping those relays to see if the compressor will run.

Knowing how the system operates will help in your diagnosis. See the summary at this link:

Air Suspension & ECATS Summary: Components & Operation

If the pressure in the system is low, perhaps due to a leak, the compressor should begin running shortly after the engine is started. It will run for up to 120 seconds unless you put the transmission in gear, at which time the compressor will shut off. It will typically not run again until the vehicle speed exceeds 25 mph, or the engine is shut off and restarted.

On our '04 XJR I have experienced the situation paydase described in which the compressor would not run again until I cleared a stored Diagnostic Fault Code (DTC). Many of the DTCs related to the air suspension are proprietary Jaguar codes with the prefix letters C (Chassis), B (Body) or U (Undefined or Network). Most standard OBDII scanners can only read the P (Powertrain) codes, so you will need to find a shop with the necessary diagnostic equipment to read and clear the proprietary Jaguar codes.

If the compressor won't run after you swap relays, it might be worth doing a hard reset. Disconnect the negative battery cable and touch it to the positive battery cable terminal (the battery will be out of the circuit so you don't have to disconnect the positive terminal). Hold the terminals firmly together for at least 30 seconds - two or three minutes might be better. This may sufficiently clear module memories so the compressor may run again.

The most common problems with the suspension seem to be the air compressor relay; a worn piston ring/seal in the compressor that prevents it from pressurizing the system as quickly as the Air Suspension Control Module (ASM) expects; and an air leak somewhere, typically at an air hose fitting, an air spring top seal, or an air spring bladder.

Please keep us informed.

Cheers,

Don

 

One air spring leaking badly will cause the whole car to drop, because the ASM tries to keep the car level at all times. While doing this, it will eventually detect the car is too low from the height sensor readings and put up the red light and warning text. Don't cause any more damage by driving the car until it has been investigated.

There will be fault codes that will indicate where the problem is located , or may be located. However, if the compressor has failed the car will eventually drop, and if an air spring has a bad leak it will also drop and the compressor wont be able to keep up with the leak.

 

Thanks everyone for the great input. The air compressor is coming on so the relay is not the issue. If there is an air leak big enough to cause this problem I should be able to hear something shouldn't I? I'm assuming the next step will be to check and see if the compressor is putting out enough volume to pressurize the system. Where is the best/easiest place to check for air pressure? I'm guessing it's going to be right at the compressor.

 

Most likely a leaking air spring. Drive a bit, then check clearance on tires. Let it sit overnight and check clearance again.

 

And take note after letting it sit overnight if it is just the front that dropped or the rear or both. The front is on a single solenoid so both sides would drop. The rear has independent ones for each wheel so could only drop one side. That would point you in the direction of a potentially leaking shock.

If you start the car and let it run at idle does it come to ride height at all?

 

I appreciate the info. It's all good info, and I'm grateful to learn it but I'm afraid I wasn't clear. Let me clarify. The whole car is already too low. It doesn't raise up when you start the car even though the compressor comes on.

I realize that the problem may very well be a leaky air shock. My question above is about the best place to check to see if the air compressor is putting out enough volume to pressurize the system. I don't want to put out the money for the shocks and then find out the compressor isn't carrying the load. So, I'm trying to find out if there is a port or valve for checking the system pressure.

 

All the TSBs I have are loaded onto this forum somewhere and GUS has them on his site.

bob

 

It may be in many places: compressor seals, connectors and airlines all around, valve block in the trunk, top of each air shock.
Try to listen carefully, hood open to start with.
In my case there was a clear whistle noise that increased when the compressor started, at that was easily traceable to be on top of one air shock; when I put my hand there, I could feel air blowing.
If not, open your boot/trunk and remove the spare wheel: the valve block is there.
For the compressor, you have to dismantle protection panels in the left front wheel arch, the compressor is behind the bumper.
Good luck!

 

Thanks! Sounds like a Saturday morning job.

 

I had a problem with my right rear being somewhat low after resting all night. It was only that corner and quite noticeable.

I loosened then carefully re tightened the inlet on top of the strut and that cured the issue for me.

So in my case only one strut was causing the problem.

Seems unlikely that all four in your case would develop leaks at the same time?

 

I found mine by making a dish washing liquid and water mix and then painting it on and around the air lines at the top of the shocks. Bubbles will show up if it's leaking. Other places to check are the manifold block and the reservoir both of which are in the trunk.

BTW- if the compressor cannot pressurize the system after running for a couple of minutes it will give up in order to not burn itself out and set a fault.

 

Thanks for the reminder of the soapy water test for leaks, raschwar.

Just for clarity, the compressor doesn't flag any faults itself. Its runtime control resides in the Air Suspension Control Module (ASM), and the 120-second maximum runtime is part of an algorithm programmed into the ASM to prevent compressor overheating, since in the Jaguar implementation there is no temperature sensor on the compressor as there is in some others (Audi, for example).

I don't know how long the ASM gives the suspension to reach its calibrated height, but on our '04 the compressor is generally allowed to run at least a couple of times before the AIR SUSPENSION FAULT is flagged.

Cheers,

Don

 

Thanks for tidying up my rather glib explanation. Hope I didn't mislead.