Can anyone tell me what the sensor pictured below does, exactly? It came off my parts car and it looks brand new. Google or eBay calls it a suspension sensor and some searching didn't find any further explanation.

It will bug me until I understand what it does...

The part number is LJA 1975 AG

 

Looks like it's an accelerometer. Which makes sense when you think about CATS only engaging when it detects 'enthusiastic' driving
SNG Barratt - The Ultimate Jaguar Parts Specialist

 

So it literally detects if I am accelerating and/or braking more quickly than "normal"?

Cool. I wonder what it monitors in order to tell that. Wheel speed maybe? Angle/level of the car?

I love these cars.

 

+1 for grandell, its shown as Rain sensor on eBay, but described as suspension sensor in description... Jaguar XJ8 Rain Sensor - 2003 XJ8 - p/n LJA1975AG | eBay

 

Kinda... It measures g force, most likely vertically and laterally to detect body roll when you're cornering hard.
If you're accelerating and/or braking hard this will trigger body roll, but it's probably not directly what the sensor is measuring

 

How many CATS supsension sensors/accelerometers are inside the XJR? Two, three?

 

There are 3 accelerometers: one for lateral, one for front vertical and one for rear vertical accelerations (g-forces). This is how the system operates (quote):

'With the vehicle stationary, the dampers are in the firm setting, but will normally switch to the soft setting when the vehicle exceeds 8 km/h (5 mile/h); all dampers are switched simultaneously.

Sudden movement of the vehicle body, in response to road inputs, is detected by the vertical accelerometers, and the ADCM switches the dampers to the firm setting to give improved damping of the resultant oscillations.

When cornering forces are detected by the lateral accelerometer, the ADCM switches the dampers to the firm setting to reduce the roll rate and improve wheel control.

When the footbrake is applied, the ADCM receives a signal and calculates the rate of vehicle deceleration. If the deceleration rate is greater than a certain threshold, the dampers are switched to the firm setting to reduce the pitch rate and improve wheel control.

After the event has passed, the dampers revert to the soft setting.'

The system does not monitor how hard you accelerate so you can floor the accelerator whenever you like.

 

Hi MS! Thank you very much for your detailed answer - helps a lot.

1.) Where are the three sensors located? I seem to recall one being in the spare tire area near the fuel filter

2.) Are all three of them the “same” part, hence the same part number?

Cheers, Oliver

 

 

Sophisticated cars require sophisticated parts Measuring a sudden change of acceleration by
making use of inertia forces using solid seismic masses which convert into electric or magnetic
values certainly qualifies.

 

I forgot to put on my pic post, note that the description says front & rear Vertical. Apparently someone has found a way to get more power out of these cars than us...

 

The parts catalogue shows that all three are same - LJA1975AA, superseded by AB, AC and AD.

 

I believe they all function in the same manner, just oriented differently.

 

Guys, thank you a ton for your amazing help! This Forum is by far the best I’ve come across.

 

Your post made me think Randy. Can said seismic masses become "stuck" over time?

My suspension fault warning light came on (and off by itself) around four months ago and kept getting more and more frequent to the point where it came on (and off again) several times a day. My XJR is a daily driver for anyone wondering.

As I knew my CATS dampers, springs, control module and wiring are all new, I was convinced that the sensors must be the culprit. So I ordered newer generation ones (mine have the AA ending) and did change the location of the existing ones. Meaning I put the rear to the front and the front vertical to the lateral side etc. Whilst having them out I shook each sensor for some time before putting them back in their different location. Now the suspenion fault light comes on maximum once a week, despite frequent trips a day which is much less annoying than 15 times a day prior to that.

So maybe this helps someone to "fix" the issue whilst waiting for replacement parts.

The error codes are:

C1516 - 5 Volt Supply - Short Circuit on Battery
C1455 - Front Vertical Acc Sensor - Electric Circuit Fault
C1435 - Rear Vertical Acc Sensor - Electric Switching Circuit Fault

 

Another meaning of C1516 is "Roll Rate Sensor Signal Fault" which is more likely to be applicable than what the Icarsoft shows. This would relate to the lateral accelerometer. It is a bit strange (but possible) that you have faults in all 3 accelerometers. Well, they are now 25 years old.