I recently began the retirement of my wife's 2004 XJ8 and replaced it with a Genesis 5.0. The Jag has been a solid car despite being 16+ years old with just a tad over 129,000 miles. I planned to sell the car but other stuff got in the way so aside from giving it a thorough detailing I hadn't driven for almost 3 weeks. The other day I realized I'd let it sit and decided to take it out for a short warm-up run only to be greeted by the dreaded RP light. Not having the time right then to do anything I checked the battery and found it to be down to 11.9 volts at rest so I hooked up my battery tender and left it alone for about 3 days. I checked it again and it was registering 13.3 volts but the RP light was still on so I took it for about a 3-4 mile run so it could warm up and get some fluids flowing, especially through the injectors.

Still had the light so I dug out my dedicated laptop with the IDS/SDD software installed that I've used for the last 6 years to take a look at the codes that should be there. Keep in mind that there were NO OTHER WARNING LIGHTS. No ABS light, no stability light, no other lights at all and aside from the ignition interrupt at 3,000 RPM's that goes with the RP light everything else was operating as it should; or at least as much as I could test as I didn't attempt a brake lock-up. Anyway the SDD diagnostic gave me no clue as after 3-4 complete scans it came back and showed me NO DTC's (not even P1000) while at the same time telling me it couldn't communicate with almost ANY OF THE MODULES !!

Come on! How does it not communicate yet not tell me there are some DTC's? Wouldn't the lack of communications itself post at least 1 DTC? So here I am with an RP light and not a clue as to what could be causing it beyond a general failure to communicate.

Has anyone experienced anything similar? I ran the diagnostic at least 3 times from start to finish and kept getting the same results and I even asked it to show me any DTC's from any untested modules. NOTHING! How can that happen?

Bad cable??? Corrupted program?? Any clues?? What should I try next as it's over 100 miles to the nearest Jag dealer and just opening your hood costs you $1000.

 

The 04's used older IDS, that will not give you access to read the engine modules with most if not all code readers.

 

I do not have SDD, my scanner iCarsoft allows clearing codes if none are readable.
My wife’s 335i throws a fuel pump plausibility every few years. Shows a car lift and goes into limp mode. Clearing it with the BMW iCarsoft scanner gets rid of the warning light and restricted performance. I usually do it twice. Appears to perform reset without a readable code.

 

Yes the icarsoft i930, as well as my Launch clears all readable codes, on the 04.
But the 07's engine module will give info to the icarsoft where the 04 will not.

 

Sounds like your SDD is 'finito' I gave up on mine years ago.

If you remember it's a case of when not if.

Suggest you buy an i carsoft.

RP may be only TPS

 

Wingrider, I've used this software from British Diagnostics for at least the past 6 years and while it switched to IDS when it's hooked to my '99 XK8 it has always used the SDD side for my '04 XJ8 without a problem. This is the first time it has failed to read the modules. It runs the diagnostics recognizes the year and model and allow me to move around to various areas of the software but can only communicate with a couple of modules. Given that aside from the 3,000 RPM ignition cut-off everything works as it should. No warning lights, no instrument cluster problems, no switches or controls that refuse to function, etc.

The problem could still be within the software as after 6 years of use it's possible that something has become corrupted but it isn't due to the '04 using IDS which is simply not the case.

 

That possibility exists and if I have too I can reinstall as I have the original software stashed away and have reinstalled it before when an earlier laptop gave up the ghost. I rather not go through the hassle if it can be avoided since aside from this particular series of tests it has worked without a hitch. Even now there are a few modules it can see but only a very few and that makes me think the problem is within the cars many systems and are the result of its having sat for 3+ weeks and the battery voltage dropping below 12v.

Today I'll do a hard reset and see if that helps any.

I've always had a laptop dedicated to doing just the IDS/SDD software and the occasional OBDII for friends non-Jag cars who need their cars read so the system doesn't get used for general computing or web surfing. Most of the time that laptop just sits waiting for it's next job.

 

It could be your dongle rather than your software that is finito.
What do you use: a clone Mongoose or a genuine one?

 

If you want try it. Purchased and gave up trying to load software. Between the server, my bandwidth, and crap old Windows machine I never got all the software downloaded.
Purchased an iCarsolf and never looked back.
After watching Brutal spend 45 minutes coding a key with the real deal I decided the “factory” system is too clunky and SLOW. I can finish a scan with the iCarsoft while the IDS/SDD is loading up.

 

I've been slow to get back on this but I worked my way through the problem.

The initial problem was a restricted performance light. The car had been sitting for about 3 weeks and the battery voltage had dropped below 12v which is never a good thing with these cars. I attached my battery tender which brought the resting reading back up to just shy of 13v after a couple of days so I ran an SDD scan.

First mistake was in not also attaching a battery charger before running the scan. In the past I have attached a charger but this time I was in a hurry and not thinking. Anyway the SDD software is slow and clunky which is especially true as the version I'm using was first written back in late 2004 and has had no updates since. It's fine for my '04 XJ8 though. Anyway as I found out the scan itself puts over a 6amp load on the battery so that in short order you end up with an erratic set of results which in my case was an almost complete lack of ability to read any of the modules and therefore NO DTC's.!!

My next try after making sure the battery was fully charged was to run a scan with the battery charger hooked up. At this point I had to basically go through the entire set-up routine that the delivering dealer would have had to do back in 2004 I guess, even though everything was working despite the RP light. In the process I wiped out the offending codes, enabled a couple of features that evidently had never been enabled or were lost in a previous servicing prior to my ownership 7+ years ago. I didn't have to reprogram any of the major systems but just basically made sure they were all talking to each other.

The '04 XJ8 has been a trouble free car compared to my '99 XK8, at least electronically and the only time I've had to run a scan on it was a couple of years ago when one of the speed sensors for the ABS went south on me.

Lesson learned. Don't run a scan with a battery charger attached to offset the load imposed by the scan and don't let these cars sit idle for very many days without a good quality battery tender attached. They're inexpensive insurance against a buggered communications system.