My 2001 XK8 exhibited numerous intermittent faults: Check Engine, ABS fail, trans fail, etc. I replaced the normal battery with an AGM and that reduced the number of faults, but they still appear. I found that disconnecting and reconnecting the battery would clear most faults, or using an OBD reader to clear them worked. I have read that these cars are very sensitive to "voltage," and will throw these bogus faults. But I'm wondering if the sensitivity is to the voltage level or to electrical noise on the power system. Our cars have lots of digital boxes. Digital circuitry is typically sensitive to electrical noise, also known as EMI or spikes or other deviations from a clean stable +12 volts. Do we know the precise problem(s)? I am going to experiment with various electrical noise reduction methods to see if I can nail this down. Join me if you have info or ideas.

 

P,
It's related to voltage level not noise. Good question though.

New battery is good, but hey you wouldn't be the first of us to find that barely visible corrosion on battery (take that term past the battery connection to downstream terminals in the trunk too) and ground connections. 12volts isnt that much EMF.

Alternator checks good?
Is there a current draw with key out, car asleep? (For example be sure the ignition key gate closes with key out)

WTH, it's easy enough to measure current draw if you're cleaning the terminals. If it's high I'll show you how to find the short measuring voltage drop across the fuses' test points. Easy stuff.

John

 

I'll clean the battery terminals and other power and ground connections to eliminate them as possible trouble. I'll check for any current draw with the car off (I'm a EE and have the tools, etc).
I keep a battery tender in the trunk and plug it in whenever the car isn't used for a day.
Stay tuned.

 

To my knowledge, the issue is voltage. On a weak battery, when the starter uses up a lot of current, the voltage drops. That drop can put digital electronics in a funk, because the simple scenario is that digital electronics is either power on or off. I don't believe there is any factory testing going on with partial voltage and recovery from that state. Proper power is just assumed.

Start with checking the power block in the trunk. It is known to sometimes loosen up and provide weak power as a result. Also check the battery cables after a while. If they are hot, it means they offer resistance and dropped voltage. Replace them.

I know there are many views on this, but these messages are really meant to help you with the diagnostics. Resetting them over and over will not solve anything. On the face of it, trust these messages and work towards a root cause. While anything is possible, electrical noise is not likely to to be the source of these cascading messages. These messages sound like data bus errors, possibly pointing to bridge points like the instrument cluster. Have you checked the TSBs for these (jagrepair has them)? There was a VIN range of affected ICs, fortunately very fixable at home with basic soldering skills. Also, the ABS module and the IC host the terminating resistors to the CAN bus, which is required for proper operation, so a failed ABS module can crash the CAN bus, leading to many messages. Those would be my starting points.

Of course once you have specific messages, search is your friend.

Best of luck, keep us posted.