Hi All-

I had a strange occurrence with a mass outage of many components at once, and I'm looking for the common denominator. I was driving my 2001 XJ8 home this evening. While sitting at a light, the radio started powering on and off for a minute and then just died. The light turned green, so I hit the gas. The engine revved, but the transmission wouldn't catch. If i slowly accelerated, I could get the car to drive, but it felt like a manual tranny right before the clutch burned out. While making the turn at the light, I noticed my power steering was out. I then tried rolling down my windows, but got nothing. The cpu screen in the dash then displayed that my brake fluid was low, then the parking brake indicator would randomly flash on and off. I know my car isn't completely possessed, so I'm wondering if anybody knows what controls all this. What's the common denominator other than the computer itself? Hopefully the car's computer didn't fry itself.

You insight is greatly appreciated.

 

Pals, first off, welcome to the Forums. I think you will find that you will like this site and there are tons of very helpful people here. But, we do ask a simple thing of you. Please stop by the "New Member" section and introduce yourself. We pride ourselves in being a different sort of car group and we like to get to know one another. This also gives you a chance to meet/learn who the movers and shakers of the group are.

Now, for your problem. I would venture to guess that you are having an issue with your alternator which is driving the system voltage down, leading to an under voltage condition. This will cause the electronics to do strange things. This can be caused by something as simple as the battery starting to go (if you can start the car and the motor cranks over with authority, then it is not the issue, but if the motor seems to roll slowly and takes a few seconds for the motor to finally catch, the battery would be a good place to start). Granted, it can still be a computer issue as the ECM controls the alternator, which then controls the car's voltage. If it is starting to fail, it can drive the alternator to do all sorts of things. Could also be the alternator going too.

I would say to first get your hands on a multimeter to see what voltage the car is running at. You can simply connect the multimeter across the battery terminals and the battery should be at 12.6 VDC (if not at 12.6 VDC, that can be either a bad battery or a potential alternator related issue). Then, if you watch the multimeter as you crank the car, you should see the multimeter drop into the 11.0 to 11.5 VDC range and then suddenly jump up to around 14.4 VDC as the motor fires. If you see the voltage drop to around 10.0 as the motor is trying to be started, then you have a weak battery and most likely need to replace that before going much further.

Once the motor catches and the voltage jumps up to 14.4 VDC, you will see it remain there for a short period of time (30 seconds or so) and then it will slowly lower to 13.7 VDC. Once at 13.7 VDC, it will stay there regardless of what you start in the car. But, I would recommend turning on the dash fan to max air flow (A/C on), headlights on, and the seat warmers (large electrical load). The multimeter should not have really moved while doing this. If the voltage did move, then you are looking at a bad alternator most likely. If you are seeing the voltage jumping around without starting anything electrical, then you are most likely looking at a bad wire between the battery and the ECM (this wire senses the voltage and allows the ECM to correct this) or you have a battery cable that is starting to go and it is causing a high resistance and driving the car's voltage down (but, this should be seen with the starting of all the electrical stuff and will show itself by having a dark spot in the battery cable where the cable is getting very hot).

If you need more help, let me know. I will assist however I can.

 

Thanks Thermo...Looks like you may have nailed it. After I posted my thread, I went back outside to start up my car for further testing, and it wouldn't turn over. I yanked the battery and hooked it up to a charger, and sure enough, it was dead. It's on the charger now getting it's juice. A full charge will be enough to get it back to my shop to test, and I'm sure replace the alternator.

Thanks again.

I'll hit up the newbie deal for an intro.

 

Pals, do not jump on the alternator quite yet. The new cars are very sensitive to electrical issues and something as simple as the battery starting to go will be enough to raise major heart ache like you saw. Get the battery load tested to make sure that it is ok (probably won't be) and then measure the car's voltage when the motor is running. Then see if you have an alternator issue or not. Jaguar alternators are pretty robust and normally do not need to be replaced. There is always the oddball out there, so, I am not ruling it out. Just past experiences has shown it is not likely.

 

Thermo.

I did a load test on the battery and its fine.

 

Thermo, thanks again for you help. With a fully charged battery, everything is back to normal. The alternator now has a high pitch whine, so it's clearly toast. Gonna r&r the alt.