I just purchased a 2005 XJR with 85k miles. When returning home i tried the ACC and it seems to work as there are no errors, but the system is clunky...meaning when it goes to slow down it slows down with hard braking. Then when the front clears there is hard acceleration. I did adjust the distance, but the whole experience is not smooth.

I've never had this type of option, but have read on this board all the praises (when it works!)....so i'm wondering if i maybe need a reset or is there some type of calibration? I didn't see any debris on the sensor and cleaned it with water/cloth.

 

You have to be careful that you don't try to cruise past, ie overtake, any vehicle that's actually moving ... even a slow moving cyclist will be detected and will set off the slowdown reaction, with the brakes if necessary. I know 'cos unwittingly I tried that when I was driving mine home straight after I bought it ! The guy behind wasn't impressed !

 

Well this behavior occurred while on the open highway cruising above 65 mph....it just doesn't seem smooth at all , but very jerky on braking and acceleration. Hard to describe, but not a pleasure to use so i'm wondering if this is 'normal' or i need to calibrate or check something. I don't have any warning lights or error codes for ACC.

 

Well, if it's as you describe and you're not passing anything then it certainly is not normal.

The only thing that comes to mind is that the detector unit, which is behind the bumper/fender cover (L/H of the number plate I think), may have come loose in some way and is somehow moving around which maybe makes the radar return from stationary things seem to be from slow moving objects.

Otherwise it must be some electronic fault within the unit and that's a specialist job.

 

THanks for the responses....and to be clear, i'm not passing anyone...just set cruise speed on major highway and set the gap....i purchased a Foxwell NT510 Elite last week and there are zero codes for ACC. I'll try to see if the mount is loose.

 

This is part of the section on ACC in the Driver's Handbook. I've highlighted part that might be relevant ...

The radar sensor is mounted behind a cover on the left-hand side of the lower cooling aperture, to provide a clear view forward for the radar beam.
• Only use Adaptive Cruise Control when conditions are favourable, that is, straight, dry, open roads with light traffic.
• Do not use in poor visibility, specifically fog, heavy rain, spray or snow.
• Do not use on icy or slippery roads.
• It is the driver’s responsibility to stay alert, drive safely and be in control of the vehicle at all times.
• Keep the front of the vehicle free from dirt, metal badges or objects, including vehicle front protectors, which may prevent the sensor from operating.
• Do not use ACC when entering or leaving a motorway.

 

I've come to like the ACC in my old Jag, though I only use it on long trips. Doesn't work well in busy traffic, IMHO

- Ditto: Make sure the grille, etc is clean in front of sensor (Try cleaning front of sensor as well)
- This is an early tech system; esp in the pre x356 models
- Mine will hit brakes when passing under a highway bridge on occasion
- Ditto someone pulling in front of me while cruising