Had my 2000 XKR on a battery tender for a few months while I was abroad working in the Middle East, and the car was down for "suspension Fault" on the dash. My intention was to replace the CATS suspension with standard Bilstein shocks, as I was having difficulty locating, and justifying the extra cost over the advantage of handling on the road. Suspension control module in trunk disconnected to allow message to clear on the dash. Front shocks fitted and new Welsh mounts fitted,( no previous experience, so can't judge yet). Ran the car for a week without a single cough, splutter or burp.
Come to the day before I leave for Iraq, and I need to move the car an inch to allow the beer fridge to open in the garage, and the usual start sequence occurs, turn the key, and it just cranks, but doesn't fire. Keep trying, but nothing, then CEL comes on, ASC & TSC warning, Incorrect part fitted, then restricted performance. Checked codes but could not establish link with both of my scanners.
I tried a hard reset but got no improvement, charged the battery and again, no improvement. My next course of action was to disconnect the battery and leave it on a trickle charge until I return from Iraq, which is 5 weeks time.
Does anybody out there have a similar experience to this?

 

Yes, Pete . . . anytime the battery voltage falls low enough to just start the car, but has so little to properly run the ECM > PCMs comms.

Long experience teaches that "charged" or even "fully charged" means nothing. Minimum 12.6V or you invite precisely those faults so, to that end, your battery tender or smart charger is essential . . . but I would add another . . . a cigar lighter USB charger that includes a central LED voltmeter for live, all the time battery and alternator monitoring. Cost $5 on eBay, although I picked up 5 for $15. Compare that to a damaged, life shortened battery.

Plenty of threads and posts here and on companion forums (XJ8 and S-Type of same era and electrical architecture) that list exactly this combination of faults. If you can't charge and maintain battery to high levels, replace. Using a smart charger, you can't overcharge any battery, so keep it connected until you use car. Only once car is running and voltage has dropped from 14.5V to a steady 13V, is the battery "fully charged". Suggest you use search tools and read extensively.

Only then, read codes, report any, but don't be surprised if all your "faults" magically disappear!

Best wishes,