So, for over a year now my 2004 xj8 has had the "Dsc Not Available", etc. random warning lights and it's time to get serious about fixing it. It also doubles-up the mileage on the odometer (speedo is accurate though) and the wipers creep up on the windshield. Another thing is I lose the speed-sensitive steering after turning the wipers on (strange). The only code had to do with the throttle pedal sensor (not the throttle body sensor).

It started last year when we finally started to get some rain, I checked/cleaned the drain pipe near the cabin filter but that wasn't the issue. It was pretty clear already. I also replaced the battery with the one recommended from Home Depot. Not that either. Also bought the cheap throttle body sensor off ebay but it caused more problems, not fewer so I put the original back in. I have also bought a new throttle body/mass air-flow sensor for $268 off ebay but haven't installed it yet. I thought I'd try the battery cable shorting trick first but I'd like to know the exact procedure for doing it first. So...

Do you disconnect both cables first before touching them together? Is the key in the On position or not in the ignition at all? Seems to me doing this the wrong way can cause an electrical meltdown!

I can't work on cars where I live so if this doesn't work (and I'm not expecting it will) it's off to the repair shop. I'd have them check the ground connections by the lights first.

Thanks! Gene

 

If you are going to 'short' the terminals together, both terminals must be removed from the battery, starting with the negative terminal first.

What is the age and condition of the battery? A failing or weak battery will cause all sorts of electrical 'faults'. When you have the terminal leads disconnected, use a voltmeter to see what the voltage is across the battery terminals. If the reading is less than 12.5 volts, the battery must be replaced for the vehicle to function correctly.

 

+1 on the above. Also do not have ignition on. Keep key out.

 

Replaced the battery 6-8 months ago. Thanks for the help!

 

Grounds connections likely IMO.

 

I hope you're right. Cheap and easy fix, if done carefully. Thanks.

 

What is the voltage across the terminals with the ignition in the off position?

 

Battery charger says 2.2 volts, 63%

 

If you have access to a voltmeter, use that to get an accurate reading of the battery voltage. Perhaps it is supposed to be 12.2 volts according to the charger?

 

Ya, that was a mis-print. Should have said 12.2 volts. I'll see if I can scare up a volt meter. Thanks.

 

If the voltage is indeed only 12.2, the battery should be replaced.

You can try charging it overnight and take another reading to see if it goes above 12.5 volts.

 

I have just fixed exactly the same symptoms in a 2005 XJ8! Wipers creeping up the glass, all kinds of warning lights, odd steering feel....the problem was in the two ground connections behind the headlamps. Remove the nut, remove the wires, clean everything and lightly sandpaper the surfaces, refit tightly. Problem cured 100% instantly - no warning lights, no wiper creep and the car runs as new. You remove the plastic shield at the front of the engine and you will easily see a ground connection on each side behind the headlamp units. Magic!

 

Super! I'll work on this over the weekend. Thanks!

 

I would also recommend using Gardner-Bender Ox-Gard after cleaning on both the post and the ground connector tabs. It's a conductive grease that will keep corrosion out, and is specifically made for just this type of connection.

 

Thanks for the tip!

Looks like I'm busy the next two weekends so it might be a while before I get to it. BTW, the only code that came up was for the throttle pedal sensor, but if the electrical system went all catty-whompus can you trust the codes anyway? Just a thought.

Again, thanks to everyone for all the help. I never would have bought a Jag without internet forums!