I have only been taking the XJL around a block once a week for the last 4 months due to the covid and have noticed something odd. The rear suspension is getting lower and lower. I no longer hear the air suspension noises when the drivers door is opened either. No errors on the dash. Any ideas?


Thanks
TJ

 

Odd...I took a longer drive, 5mi at high speeds and everything is back to normal. I wonder if the car was in some sort of 'service mode' that cleared? I did replace the rear brakes and had not gone over 20mph or traveled over 1mi since install. This more typical trip put the system back into operation.

 

I'll speculate. Because many things draw current while the car is off and locked, I think the short drives you've been taking are not sufficient to charge the battery. The XJ manages the power draw and shuts down lower priority circuits until the battery is returned to a sufficient charge to run everything. Many of us have invested in a battery maintainer during this pandemic because we're not driving our cars enough.

 

Good thought, but there was a maintainer on the car.

TJ

 

Found it...mystery solved.

PRINCIPLES OF OPERATION - AIR SUSPENSION SYSTEM The air suspension module adjusts the quantity of air in the springs to maintain the rear suspension at the required height. The air suspension module calculates a target height for the rear suspension based on the average height of the front suspension. If the actual height of the rear suspension is outside the tolerance band for the target height, for a given length of time, the air suspension module then adjusts the actual height to the target height. The normal tolerance band is ±9 mm (0.35 in.). This changes to ±3 mm (0.12 in.) when the vehicle is parked for 5 minutes with the engine running and all doors closed, or by putting the air suspension module into a special mode using Jaguar approved diagnostic equipment. When a door is open the tolerance band changes to -5/+20 mm (-0.20/+0.79 in.). To decrease suspension height, the air suspension module opens the exhaust valve in the air compressor assembly and the air spring valves in the valve block to release air from the air springs. To raise the suspension height , the module opens the air spring valves to introduce air into the air springs using air from the reservoir and/or the compressor. When vehicle speed is 22 mph (35 km/h) or less, the air suspension module normally uses air from the reservoir when it needs to raise the rear suspension. This ensures that the occupants are not disturbed by noise from the air compressor assembly. However, if the rear suspension is more than 30 mm (1.18 in.) below the target height, and there is insufficient pressure in the reservoir, the air suspension module uses the compressor to lift the suspension. When the rear suspension is more than 50 mm (2 in.) low, the air suspension module also sends a signal to the instrument cluster on the high speed CAN bus to display a Suspension Too Low message. If the vehicle is stationary the message is displayed with an amber triangle warning indicator; if the vehicle is moving a red triangle warning indicator is displayed with the message.

 

On my X350, you had to get above 35 mph before the system would kick in and adjust ride height back to normal. I think the lack of more frequent use and just going around the block let things blead down causing your low rear ride height.

Is the X351 also air suspension at the front? Perhaps it is traditional springs in front? The X350s had a lot of problems with ride height in front due to the air shocks developing leaks over time. The rears did not seem to have the same problem. But without regular use, a slow leak at the rears would not be brought back up to pressure.

 

Mike... thanks for the info. The x351 just has rear air shocks. It seems like getting the car up to a higher speed corrected the condition.