My 2002 XJR has been acting up recently .. just under 70k .. garage queen. It was used often when first purchased .. after a few years of ownership I took an overseas position -- car sat in the garage. When I returned it would occasionally throw the fail safe/ restricted performance warnings .. also the ABS/ TRAC. I was advise to exercise the TPS/PPS by pushing the pedal to the floor 40 times every day prior to starting the car. This eliminated the problem after about a week ... have had no trouble for years.

About 6 months ago I started to get the ABS warning occasionally ... rarely at first .. then every time I used the car. A few months ago while driving to my country place from NYC .. just as I was pulling in to my driveway ..the car went into restricted performance . The car remained at the house for a few weeks as I tried to figure out what to do with it .. every time I tried to move it .. restricted performance/ no ABS/TRAC. Getting numerous codes -- mostly the PPS. A couple of weekends ago the car stopped going into restricted (not sure why) -- still no ABS/ TRAC. I decided to try and drive it to my house in Philadelphia ...near the mechanic. It went into restricted 4 times on the drive -- I had to pull over and restart .. did not think I was going to make it. Went out of the country again .. car sat for three weeks. Returned to a dead battery -- unusual. The battery is not new .. but always showed full voltage and quickly started the car ... I guess you can see where this is going.

I jumped the car and drove to Pep Boys with the ABS/ TRAC warning in my face -- $120 later and new battery ... I start the car ........... no warnings. I drove the car around for a few days -- close by ... no warnings. Monday I drove it to NYC -- Tuesday from NYC to Hartford .. and I just drove back to Philadelphia from Hartford this afternoon ........ nothing .. no warnings.

I guess the battery was weak ?? Every time I got the failsafe -- the car was coasting at slow speed (coming up to a traffic light)... I'm thinking that at low RPM's maybe the alternator was not keeping up or the volts were not stable .. the battery being weak was not able to stabilize the voltage -- I have no other idea.

I'm really shocked .. I know all to0 well about the need for a good battery ... but this really surprised me.

 

What amuses me about these cars is the way the batteries don't give you any normal signs they're on their way out. On a normal car you'd get signs like a sluggish starter or something, but these either spend their time throwing codes or, as in my case, start normally forever then won't turn over when you really need it to.

Now when I buy a new battery I put a label on it with the purchase date on, then when the guarantee expires I replace it. If something happens before then I get it dealt with through the store I bought it from.

Glad you solved your issue though.

 

I'm one of the people alway talking about needing a good battery ... I never suspected it. It tests fine .. but it did go dead .. or bellow start volts after three weeks. To be fair to the battery -- I started the car many many times with little driving ... car started perfectly every time. No headlight dimming ... etc.

These cars can be frustrating, in that the faults are intermittent. Thinking you fixed something, only to discover you actually did nothing.

The fact that I would not get a drive cycle without the ABC/TRAC prior to the battery replacement ... and after it never came back is telling. I only thought about the coasting/ alternator output theory after I got the new battery.

The AC compressor clutch on both of my current X308's creates a current/ volt fluctuation .. my prior one also. I'm wondering if it could have been the clutch engaging as I was coasting into a light that cause a volt drop and the car to enter failsafe? The AC is powerful -- maybe it has a larger compressor and so need a more powerful clutch? The compressor on my X300 was huge -- the x308 has a different one .. so I don't know .. hope I never see mine.

This is so strange -- I'm searching for some logical explanation.

I hope this was the fix .. I was about to take off the Tbody and send it out -- same with the ABS pump

 

If you're going to regularly leave it for a while (more than a week), you should get a battery maintainer. I have a couple of Noco Genius tenders that work great.

The problem is that when the battery is left for longer than that without charging, you start sulphating the plates, and losing capacity.

 

I connect my 911 to a maintainer as it will go dead in a month -- my old SL can sit for months and months and start right up -- That battery is from 08.

I use a maintainer on my tractor !

 

"my old SL can sit for months and months and start right up"

The fact that it will start up is a poor indicator of battery condition. It only takes 5-10% of the rated charge capacity to start the car. Even a battery with no load at all (probably the case in your old SL) will slowly self-discharge, and any time it is at less than 100% you start losing capacity, permanently, to sulphation.

It is common to assume that an old battery, like your one from 08, is fine as the car still starts. However, it could have lost 90% of its rated storage capacity, which isn't so great, is it? That's why they seem to suddenly fail. The capacity finally dips below what's needed to start the car, probably on that really cold morning.

 

LOL I gave someone a jump-start once with my first car, and later that day MY battery was dead! It would seem I'd given the lad I jumped all my juice!

 

Update: With no issues popping up -- figured I would risk the old girl and take her to Maine for some late mid-state fishing. Took the back way from NYC -- and really got on her. Came back to PA Friday .... never a warning light. The ABS warning never coming back is a real surprise.