Thanks again Thermo. My mechanic replaced the positive cable (only) today and the 2 volt drop remains at approximately the 2 mile mark.

Could the negative cable ALSO cause this issue?

I will give all of your info to my mechanic. Hoping something works soon!!

 

Yes, it could be caused by the negative battery cable. Like I mentioned with the alternator wire, the negative battery cable can do the same thing. This is where putting a multimeter across the battery can help determine what is going on. Your mechanic should know what checks to make for that. If he is in doubt, let me know and I will give detailed instructions on what to do.

 

Thank you so much, Thermo. I will give all your notes to my mechanic tomorrow and hope that something wonderful results. I really appreciate your help!

 

Thermo - Why would it be that after the voltage drop (14.6 to 12.6) I can turn the car off, wait a minute (or less), turn it back on and the voltage is back up to 14.6 where it stays for another 2 miles - and it then drops down again.

If it were a matter of overheated wires (bad ground or connections), they wouldn't cool down that quickly, would they?

Obviously I am not a mechanic, but doesn't this sound like something going awry in the ECU?

I haven't had a chance to do your suggested test yet, but very much appreciate all your advice.

 

CaliforniaGirl, keep in mind that if you have a bad wire, depending on how it is failed can cause all sorts of different indications. You also need to think about how the engine moves when you say start the car. It moves much more during starting that it does at any other time. This "shaking" can move the wiring just enough that it makes contact again. I do agree that the bad point would probably not cool down quite that fast, but if it is right on the cusp of being a problem, a little bit of cooling can do wonders.

I wish I could have you come over to my place as I could put my multimeter on the car and get most of the questions answered in no time flat. While I do live in California, I live in California Maryland (yes, it is a town in the state of Maryland).

Just to give you an idea of what is going on, when the voltage drops from 14.6 to 12.6 VDC, what you are seeing is the alternator's output falling to essentially the battery voltage. You can think of it as the alternator is not outputting anything and you are simply running off of the battery. This is why the voltage doesn't drop all the way to 0 VDC.

 

My mechanic replaced the negative battery cable today and checked the voltage at the battery (between 12.2 and 12.7). I again drove off after starting the car with the voltage on the TEST display at 14.7 - 14.8. Again, after approximately 2 miles, the voltage dropped to 12.8 - 13.0 range.

My mechanic says that as long as I am above 12.4 the battery IS being charged and I should not worry.

Since I have been reading the TEST mode, the battery light has not come on, however, it does not seem right to me that the voltage should drop this substantially at the same point in each drive.

Is there any way that this could actually be NORMAL? Could it be that the ECU is instructing the alternator to charge at 14.7 - 14.9 for a certain period after startup to compensate from the loss of charge AT startup, but then, after reading the battery (if it is almost fully charged) adjusts to a lower level (12.7 - 13.0)?

I DID run your suggested test today (revving the car to 4000 RPMs in neutral after the voltage drop) and the voltage did NOT rise. It stayed at 12.9 with NO accessories running.

My mechanic also claims that the "first thing" he did was check the field voltage going to the alternator from the ECU and that this, too, was all good.

I need to take a short trip (200 or so miles) this weekend and don't know if I should rent another vehicle or if this one is safe.

Yes, I, too, wish I were in YOUR California so I could get this solved.

Thanks for your ongoing help. It truly is appreciated.

 

CaliforniaGirl, the ECU (what is controlling the alternator) is programmed from the factory to artificially raise the voltage output of the alternator right after start up and hold it there for a period of time until it thinks the power pulled from the battery to start the car has been replaced. So, yes, for the first 2 minutes or so, the voltage will be higher than at other times.

Having the voltage remain the same while revving the engine is telling me that the ECU is controlling the voltage, not being limited by something else.

Please keep in mind that the ECU senses the voltage at a different point than the output of the alternator. It actually measures the voltage inside the cabin of the car. I know, confusion (blame an engineer on that one). The best advice I can tell you is to find a friend with a multimeter. Set the multimeter to the 20V DC scale. Put the red lead on the battery + terminal and the black lead on the - terminal. Make sure the multimeter leads are touching only the center post of the battery, not the battery cable clamp. With the car off, it should be at 12.5-12.6 VDC. With engine running, it should be up at around 13.5-13.7 VDC. I would not necessarily go off of the instrument cluster. As long as your multimeter is reading over 12.6 VDC, then your battery is being charged and the alternator is handling everything.

As for your trip, hop in the car and go. It sounds like the battery cables were not helping things out and with the new cables installed, you should be golden now. Enjoy the kitty!!!!!!!!

 

I think I may actually be able to sleep tonight thanks to you.

Yes, my mechanic measured the battery terminals and found a range of 12.4 - 12.7.

With the engine running, it was 13.0 - 13.2 (not as high as what you suggested, but better than before the salvaged Jaguar alternator and new battery cables were installed).

Today, it was 110 degrees F. in Los Angeles and (while running in TEST display mode) the car stayed above 12.4 (closer to 12.6 and 12.7) even with the A.C. running.

No battery light came on - MUCH to my relief.

Tomorrow is supposed to be another scorcher and my PTSD will probably force me to check the numbers until the heat dies down - BUT, at least I do not feel compelled to trade my car immediately!

Many, many thanks to you for your smart and steady responses to my plight. I am very grateful and so is my "Jackie."

 

CaliforniaGirl, take it easy. All is good now. Besides, have the people at the far end of yoru trip have a nice bottle on ice waiting for you to give you something else to be looking forward to than worrying about the voltage of the car. That or find someone to drive the car for you so you can be in the back seat drinking a few there.

Just a brother in arms helping out those around me.

 

Dear Brother in Arms - You HAVE been a very big help - and it seems to have some good advice on conquering worry as well. I will remember your kindness!

 

CaliforniaGirl, pay it forward. Find a fellow brother/sister in arms and show them some love when they are feeling down. I am sure you can relate to them better than I ever could. Sometimes what people need is not money, but a helping/caring hand.

 

Yes, Thermo, thank you for MORE wonderful advice. I actually had an opportunity to pay (part of it) forward today and will remember to keep the caring coming. So very glad to have (virtually) met you. Hoping life is treating you as well as it ought.

 

100% Alternator. My first X Type acquired when it was 9 yrs 3 months old, after driving for a month, the batt lights lite up and its the alternator. Scrap the car on its 10th year. Bought another X Type, it was 7 years 4 months old. After driving for a month, batt lights lite up. Car dealer wanted to repair it and car was in and out of the workshop for 3 to 4 times and eventually i change a new alternator at my own cost.


I SERIOUSLY HAD ENOUGH OF THIS CAR. I AM GETTING RID OF IT.

 

Thanks to all for the great advice in this thread.

I have a fresh issue with my 2004 X-Type, would greatly appreciate any further advice.

Problem: The battery light is on, and the battery is clearly not charging, frequent jump starts required. The problem first occured 2 days ago, and has been consistent since.
(May be worth nothing that the last drive prior to this, the engine overheated to a "red light" degree just prior to reaching home & parking, overheating due to (probably) a failed Fan Control Module - awaiting replacement, due tomorrow. - perhaps the overheating accelerated a part failure?)

Alternator was replaced approx 3 months / 3000km ago with a refurbished one. Got the battery professionally tested today (on a "1 minute test machine"), result was "Good", but undercharged. I am unsure how accurate such a quick test can be?

Note: in my work on the car today, for some reason the headlights now stay on when the key is on. Turning the headlight knob on/off only results in changing the status of the dash lights - the headlights now insist in remaining on, until I turn the key off.
This means for most voltage tests below, you can assume the headlights are on....:-/

Status: She will generally start if it's been running recently...but if she's been sitting for more than an hour, then a jump start will most likely be required...

(Current testing, after sitting for an hour)
Voltage at rest: 12.5VDC (key off/headlights off).
Voltage with key on: 11.5VDC (headlights on)
<car would not start, jumpstarted again at this point>
Voltage (from multimeter): 13.8VDC, Voltage (from TestMode/Dash): 13.2VDC (0.6VDC difference)

Yesterday:
1) Revving to 4k would not trigger the battery light. But turning on the dash fans, then revving to 4k would reliably trigger battery dash light.
2) Voltage drop on cable from alternator to battery +ve, was 0.15v when idling (tested when engine was cold).
Today:
3) I replaced the +ve cable from battery to fuse box, with a 36" 4 gauge, sanding and cleaning all points. (Original cable was 26", available local choices were 24" or 36", I see now that by avoiding the original cable routing, I probably could have got away with even just a 12" cable...) The cable lugs that were immediately available to me,, have holes approx 2 or 3mm greater diameter than the original - not ideal. But well seated
4) If anything it now seems, if anything slightly worse - in that the battery light now comes on almost immediately - < 2 min.
5) The headlights now stay on when the key is on - the headlight control knob now only affects the dash lights.
6) With battery light on, revving to 4k with no accessories, results in no voltage changes - seems stable, about 13.2VDC as per dash reading.

Based on this thread, I think my next move is to change the battery -ve ground cable. Thoughts?

Questions:
1) Is 4 gauge fine fine for replacing the cables, or should I use 2 gauge?
2) Is it a (significant) issue that the cable lugs are a few mm bigger diameter than the posts they are on? (Assuming they are clean and well seated, with correctly sized washers). I was not able to quickly source a cable with the exactly correct lugs (as they are different on each end), and I do not have a crimper at home to make my own. There will be a few square mm near the center of the lug that are not making contact.
3) Why do the headlights now not turn off when I turn the headlight knob to the off position? Stuck relay? Perhaps a relay welded closed from one of the jump starts?
4) What is the precise procedure to check the voltage drop across the -ve ground cable? Should I check from the battery -ve terminal to the bolt that connects the cable to the engine block? Or should probe a clean spot of the engine block or chassis instead? Is a test when idling fine, or should I get the engine nice and hot first? (easily done with a broken fan control module

5) Can I 100% eliminate the alternator & battery from this equation, based on the above test results?

5) Is it likely to be something other than the -ve ground cable? Have I missed something?

Any pointers greatly appreciated! I love this car, but she takes some work indeed...

 

As per your lights, my understanding is Canadian Jags have DRL (daylight running lights) on all of them. In fact Thermo (a guru here) has advised more than 1 person if they wanted that here in the U.S. a quick way is to buy a Canadian light switch and change it out. He also has another way of doing some work behind the switch with wiring to get the same result. So I believe that "worry" is actually how they are supposed to work.

As per your battery test. You really need a load type test which is not a "1 minute test". They told me 30 minutes for mine and it actually took 45. It fully charged the battery then puts a load on it.

As for battery volts, looks low at rest. When started, the correct alternator for our Jags has 3 time settings based on load, need, etc. It then charges at 15+ volts for one of 3 given periods, then reverts to the 13+ V. You can do a search on here for specifics of exact numbers and times if interested. Posts by Thermo are very precise, exact and easy to follow. Thermo and others also have a very simple test to check for a battery cable problem, just search.

 

Lights: Thanks for the info. The behaviour is definitely new. Last two years the car is parked 2"' in front of brick wall, so every night I would see the wall light up when I turned on the lights. The most logical explanation I can come up with is perhaps I accidentally fixed a broken DRL circuit? (When installing the cable to underneath the fuse box, I noticed mild corrosion in a number of areas, so I cleaned up many contacts...)

The jag always had lights on at the front (small bulbs inside the high beam enclosure). But now it is the low beams that are on all the time....I would really prefer this wasn't the case, for example driving through a campground slowly at night, I don't want to blind other campers...

Do you know if the DRL lights for this model are the small (dull) lights inside the high beam enclosure, or should it use the standard low beam headlights?

----

Thanks for all the other advice. I did a voltage drop test on all cables, while cranking the engine (great tip!), and the -ve to engine block was the culprit - 1.3v loss. Replaced it with a new cable, and all is golden, as is this forum.

To answer my other questions, for any later viewers:
1) Thermo recommends 2 gauge, although "you can get away with 4". I would recommend following Thermo's advice :-) In my case there was only 4 gauge available at this time on a saturday, and I needed the car, so I used new 4 gauge plus kept the original cable installed, until I can swap them out with 2 gauge later this week.
4) For checking the voltage drop across the -ve ground to the engine, it seems function to test on any (clean/secure/sanded) part of the engine block. Regarding heat: It seems reasonable (to me) bring your car up to operating temperature before performing these tests - as resistance increases with heat, and you want to test the cables resistance/voltage drop in real world conditions. (please do correct me if this reasoning is faulty)

Thankyou so much.

Julz.

 

The DRL are regular bulbs as are the high beams (H1) which makes carrying an extra bulb easy on stock X's. In mine, I have HID conversion on low (your DRL), HID on high (so 4 showing) aftermarket FOG matching (so 6 showing) 6,000k color of HID's & added 2- 20X 6,000k LED DRL light bars (8 showing) & left the halogen for brights. Changed all marker, interior, rear running and brake lights to LED. Left turn signal standard so I don't have to add the resistors to compensate and 400 lumen LED back up bulbs.

 

Tryed charging the a.c. kept blowing fuse someone stick a knife in the fuse slot an then it killed the car an the battery light came on an it blew a diffent fuse fixed that battery light stayed on. Cruise control unavailable has been on the dash for awhile before the battery light came on an and now the car is in restricted performance mode. Please help

 

Thanks, especially to Thermo, for all the sound advice. Have just hit this problem with my 2009 2.0 diesel estate. However, before tackling this I thought I may as well sort out my increasingly rattly crankshaft pulley (the noise was getting very embarrassing driving around town and worse still in underground carparks).

Nice easy job provided you have an extension for your breaker bar that lets you work outside the wheel arch.

Started the engine to enjoy the quietness and was happily surprised that the battery light did not come on. I've done a couple hundred miles since and still no light.

My best guess is that the crankshaft pulley was so bad that it wasn't driving the auxiliary belt 100 per cent effectively.

 

My battery light recently came on while driving normal speed just 2 days ago. I got back home, let the car run a while, and turned it off. I re-started the car and it was gone. Today, on the highway while merging into the left lane, it came back on. I tried turning on all the lights and stepping on the brake-- no differences. I drove it roughly 20 miles, got back home, turned the car off. I started it up again to go to the cemetery merely 0.8 of a mile away, and drove the cemetery and back home, and light did not come on. Just now this evening I was going to get a coffee, started it and light came on. Battery is brand new, less than 1 year old. Everything seems fine. Also, unable to pop good because the latch came detached from the lever, and the hood locks in 3 places it appears-- not sure now how to access the engine bay. Any advice, experience or tips will be greatly appreciated.

Side note. About 2 weeks ago I left the country so my car sat for about a week. I came back and it started right up. Possible influence? I am lost.