Sometimes when I try to start my 2001 XK8 I will get "trac fault" and "ABS fault" and "transmission fault" and "engine failsafe mode" and the car won't turn over. But it's not always that way. I can come back a while later and it starts with no problem. Loose connector(s)?

 

It very possibly needs a throttle body. With the fault messages you’re experiencing, and the fact that the “engine failsafe mode” message generally only comes on with throttle body failure or brake pedal switch failure, that’s what I would be considering. I have a 99 xj8 vdp and everything should be the same.

 

Any codes? And does this happen only when cold, only when warm, or both?

 

It's not frequent enough to tie it to anything. I drove today and car was OK hot and cold. Where would I see codes?

 

Sorry, should have been clearer, OBD II codes determined from the car by connecting it to a code reader. The car keeps track when things go wrong (often keeps track of things like you have seen), and it can give you an idea of what has happened. Autozone or Advance Auto can read the generic codes for your car if you drop by and ask them. That might be your first best bet. The dealer or local independents can likely tell more, but will likely cost something.

Does it ever do this while you are driving?

 

What is the battery voltage when this happens?
You need to diagnose things if you want to repair it.
We can all guess but there needs to be tests performed at the time this occurs.

Low battery on these cars is a common problem. How old is the battery?
Maybe a load test on the battery?
Maybe look at ALL the modules for network codes?

bob

 

when I first bought my car, an ‘02 XKR, I had VERY same issues as you do. After doing a lot reading on this forum, I decided to purchase a new AGM battery ( NAPA Premium Series) even though the existing battery performed OK. .

More importantly, I put my Battery Tender leads on the car permanently, and always hook up the tender whenever the car will be sitting overnight or longer.

That’s all it took to banish my electrical gremlins. These cars are very particular when it comes battery voltage, but the fix is generally not difficult or expensive.

Z

 

Battery was a problem with my car also. I was told(by dealer, of course) that the batt was new. Not the case (imagine that?). Replacing batt took care of most of the codes.

 

I bought a code reader today and will see what it says. And I will check on the battery today. The problems haven't happened when driving, just when trying to start. Stay tuned.

 

I get a code P1642 which translates as CAN DATA BUS- circuit malfunction. Well, that's not very specific. Time to check on the battery.

 

Battery is a Bosch, looks new but can't find a date on it. Measures 12.3 no load, which seems a bit low. I put a charger on it and we'll see what happens. Next week I'll pull it and test it at a garage.

 

Bosch 49-850B, SKU 9073755: bosch Standard flooded lead-acid. Cover over vent caps, but the vent hose wasn't connected. I use Optima AGMs in my other cars, but they don't seem to have a group 49.

 

If I need a new battery, Costco has the Interstate H8 (49) AGM for $178. What brands have you had good luck with?

 

Battery check is great, as Bob noted, often a source of electrical gremlins.

If the battery is good, and you still get this, it's indicating a CAN bus fault, means the electrical connection between the ABS module, transmission control module (TCM), engine control module (ECM), gear illumination module (receive only), and instrument panel (INST) is shorted somewhere, or one of the modules is having difficulties. First and easiest thing to try is to take the easy connectors off (ABS, driver side/front of engine, TCM and ECM under the box, passenger side near the firewall) and clean them with electronics cleaner on both the module side and the connector side. Unfortunately, this can be very easy to troubleshoot, or very difficult, or somewhere in between. Something helpful, perhaps, would be the electrical diagrams

http://www.jagrepair.com/images/Auto.../jagxk2001.pdf

 

Well, several hours at 8 amps and the battery is supposed to be 100% charged now. Went for a drive. Then checked and the code did not come back. Not sure if that is a definitive test. Will continue to monitor for codes and the battery state. Thanks to all for helping. Will update if things change.

 

NAPA sells a very good AGM battery for our cars.

Z

 

In July 2018 I installed the Bosch vented AGM battery that Pep Boys sells. They very kindly gave me one free to replace the failing Bosch vented wet-cell battery I had purchased from them less than two years before. No problems thus far with the AGM version....

 

4 days have passed. No codes except P1111, a Jag code meaning "systems ready." Went for a spin, came back and shut it off. Tried to start and got the string of bad msgs and no crank. Battery read 12.3, which the charger says is only 65%. I'm thinking I have a bad alternator or battery. Charging now and we'll see. Hope it's the battery, that's a quick and cheap fix.

 

a new battery is a definite plus. However, in my view it’s only 1/2 of the solution to the slew of error messages. Even with a pristine battery and an adequate charging system you STILL HAVE a car full of wiring, connectors, and electronic circuits that are 20 years OLD. These components do NOT conduct electrical current and voltage like they did when these cars were new.

No way.

You can economically mitigate the effect of this aging by keeping your (new) battery hooked up to the battery tender of your choice whenever the car is not in use overnight or longer. Is this a bandaid ? Yes it is . But it sure beats replacing the aging wiring and electrical components. And it works (without breaking the bank) for many of us who have experienced the same irritating error messages.

Z

 

Aha! After a few hours on the charger the car started. Now...with the car running I read 14.1 volts at the battery, which would indicate the alternator is OK, n'est-ce pas? With the car off the battery reads just 12.3, not a good number for a freshly charged battery. I believe a new AGM is in order. Any comments from the peanut gallery?