2003 XJ6 X350. For the last few months the rear suspension seems to be stuck in firm mode. There are no dashboard warning lights, and SDD shows no error-codes. Running SDD live data tracker, I can see rear suspension switching between soft and firm as expected (firm when stationary, and on excessive cornering/braking). Suspension works perfect in all other ways - always levelling perfectly, never sinking. Tried disconnecting the battery over night - no change. From the forum threads it seems very unlikely it is the ASM. It also seems unlikely that both struts will not react on "soft"-voltage being applied from ASM, as both left and right side is firm. Help.....

 

If you're seeing the ASM commanding the rear damper setting changes, (hard/soft), and nothing happens at the shocks themselves it implies a circuit failure between the ASM and the shocks, but this would cause an error code. The Hard setting is with no volts supplied, the Soft needs a voltage to the shocks. So, to go from Soft to Hard the voltage is switched off.

Any event you can think of that might have caused this issue ? A braking problem which throws an error code may cause a Hard default.

 

Hi a04054,

Those are curious symptoms. It would seem unlikely that the ECATS solenoids would fail in both rear air springs/dampers, unless an electrical surge damaged them, but we would expect that to trigger the CATS FAULT warning on the instrument cluster. If the electrical connectors on the tops of the dampers were disconnected, or their pins were bent causing an open circuit, we would expect the same.

The ECATS valves in the dampers are controlled by the ASM via Pulse Width Modulated (PWM) signals. It seems possible that corrosion on or looseness of electrical connectors, or corrosion on ground points could cause a problem with either the signal amplitude or quality, interfering with correct ECATS valve operation.

It would be worth cleaning the electrical connectors at the ASM and the ground it references. The electrical guide shows the ground on the right side either under the rear seat or the rear door trim or rear floor carpet, but on some cars I think the ASM is grounded on the rear inner fender with the Rear Electronic Module (REM).

According to the Electrical Guide, three of the four ECATS solenoid circuits pass through a black 8-way electrical connector under the rear center console. Curiously, the circuit for the right rear solenoid is shown to connect directly between the solenoid and ASM without passing through this connector, which could either be due to the proximity of the ASM or to an error in drawing up the schematic.

You can download the Electrical Guide here:

Jaguar X350 Electrical Guide 2003.5

Just thinking out loud, it would be worth reviewing the conditions that cause the rear suspension to go firm but not the front. For example, the rear is supposed to go firm to reduce squat during acceleration. I wonder if a problem with one of the accelerometers, the brake switch, brake pressure switch, engine torque signal or their CAN signals could cause your symptoms without triggering a DTC? Or, is it possible you have DTCs for one or more of those but had not associated it with the suspension?

Cheers,

Don

 

Thanks for your answers.

My understanding is that the sensor(s) I select in SDD shows the actual output from the ASM. Can't remember exactly, but it is named something like "left rear damper state". I take this to be the signal sent to the dampers after all the logic is calculated. Watching it switch between soft and firm as conditions change (hard braking, standstill, cornering) tells me no other sensors or stored DTCs are inhibiting operation.
That leaves electrical issue as the remaining possibility. From experience with Citroen suspension (it also uses "cut-up" 5 Volt signal to keep hydraulic valves open), the output Transistors tended to burn out. I take it this is not common on the ASM?
For testing - supplying the damper with a steady 5 Volt signal would not instantly kill the coil/valve in the damper? Would it even survive a permanent 5 Volt signal...?


Regards
Glenn

 

One would THINK that IF 0-5Volts are the parameter's that adjust things, then you should be fine. But that is only a guess, on my part!!!!!

 

Hi Glenn,

Our moderator Cambo tested the actual signals from the ASM to the solenoids and found them to be pulse width modulated with an amplitude of 5 volts, a frequency of 400 Hertz, and a pulse width of 1 millisecond. He posted a photo of a scope display of the signal, but the photo has unfortunately disappeared.

It is likely that briefly applying 5 volts DC to the ECATS solenoid would do no permanent harm, but if you fry your solenoid, please don't blame me!

One thing I may have forgotten to mention is that if your version of SDD offers the option of resetting/reprogramming the ASM and if you're using a good stable interface cable like a Ford VCM or Drew Technologies Mongoose, it might be worth a try. Jaguar insists that whenever module programming is done, a low-noise stable power supply with a current capacity of at least 50A must be connected to the battery to maintain system voltage and current during the procedure. Jaguar specifies the Midtronics PS-550C, but some of our members have found working alternatives. Jaguar warns against using a battery charger for this purpose since many "smart" chargers vary their voltage while charging and may even pulse the voltage to reduce sulfation on the battery plates.

Cheers,

Don

 

Haha! (or maybe it is more Ahaaa).. Did an experiment this afternoon: Unplugged the electrical connectors at the rear struts, and connected some 200 Ohms resistors in the connectors to keep the ASM happy. No alarmlights lit, and the suspension stayed level (have learned that just unplugging a strut raises the rear suspension quite a lot).
Rolling out of the driveway it was immediately clear the suspesion was stiffer. Out on the open road there was no doubt - the suspension was meaningless firm - almost like riding on the bumpstops!
Reconnected the struts, and the suspension got back to its normal "somewhat to firm".

This tells me everything is actually working - even the damper solenoids. What has happened over the last few months is that the dampers have gone from "borderline soft" to "somewhat to firm".
The car has rolled 200,000+ kms (130,000 miles), so I guess the dampers could be worn out. Read in another thread about how the gas in the dampers kept the oil from "going bad" - would expect a worn damper to go soft, but maybe the oil has gotten contaminated in some way, increasing the damping ability...?

Anyway, I guess new struts is the answer to this one.

Regards
Glenn