I recently picked up a 2005 XJ8 with only 28K miles for my daughter...I have never really worked mechanically on Jags but I've owned an auto body shop for over 30 years in the Los Angeles area - so I am not a novice either. For the life of me, I cant reset the check engine light on the XJ8. I finally gave up on trying/using my Snap-on Mt2500 and the SOlus system and took the car to the dealer to have it reset. Unfortunately, the light came right back on. Their code is : High Low voltage Fault and of course the nice tech service advisor told me that I should buy a new alternator, battery and cables. I have tested the elctrical system myself several times...The battery shows a steady 12.7 and a 14.7 when the alternator engages. The car runs perfect, no dimming lights, no issues. Can someone think of a reson for that code? Does the alternator have a bad regulator (maybe?) Any input would be greatly appreciated!

 

If it is the alternator, that should be covered under the original warranty, after all, its just at 3 years old. You remember your warranty expiration date? High/Low fault...can't be cables or battery if you are getting those readings. Once the MIL was reset, did you get an immediate reappearance once started...and before it was driven away from the dealer? What sensor detects this High/Low reading anyhow...is a module connector perhaps not secured in the car somewhere...you know, that monitors this? thinking out loud...

Just a tip - if you feel the need, if you want to (or plan to reset the indicator and read Jag codes frequently), look into the AutoEnginuity scanner for Windows. It works like a charm for about $500.

Did you ever get your buyout-totaled 04 XJ started BTW? You didn't post any updates since October on that issue.

 

Yeah - I got the 04' started. I plugged/unplugged a couple of the coils, pushed all the fuses back into place and it started right up. As far as the 05' XJ8 the codes re-appear (according to the dealer right away) so the light goes right back on. Like I said, with my scanner I wasn't able to reset it at all. Obviously the dealer is able to connect and retrieve info from the ECM. The funny thing is I didn't get any code # from the dealer - just the High/Low voltage issue - so I assume that is what their scanner reads. It's just odd that they suggested replacing the Battery, Alternator and connecting cables (in that order) I Imagine that they've seen this issue before. It just seems like a remove/and replace until you find the bug thing...I was hoping that they would pin point/troubleshoot more accurately. Again, any input would be welcome!

 

See if you can get a code number, if possible. There are a couple techs on here that are pretty good at diagnosing from just the code, and can at least give you an order of importance of things to try for the fix. If your scanner doesn't read it, the engine codes can most often be read by any good scanner, an autozone, o'reileys, etc can scan them for you at no charge. My autozone had problems with mine, however. That's when I bought the software that i recommended.

 

I tried 3 different scanners, 2 of the gave me the "no codes found" one gave the P1000...The dealer did not give me any code number for the check engine fault. It did give me a code for the ABS fault which the car was showing also( 1145 - ABS sensor) but for the check engine - only the "High/Low Voltage" thing. I was aware of the ABS sensor but I wanted to play it dumb and see if they actually give me the correct reading (which they did). Interesting, No?