I have had issues with my 1999 X308 126k not holding the battery charge, ie after a day or two I got traction control failure messages and and radio would switch off. Since the battery was old (4-5yrs) I just bought a new one to see if this sort things out. It did not.

However although I have no warning messages or warning lights on the dash I now suspect the alternator after following the fault finding procedure. Which is basically switch all electrical loads off and start the car when cold. Then disconnect the battery neg. Theory being if the car engine stalls then the alternator is doing zip, if the engine continues to run then you have chance to measure the charging voltage. In my case the engine stalled. Conclusion duff alternator or wiring. Connections all look good.

So am I am now at the point of thinking to get a new alternator. There appear to be me to be about two choices. a) Original DENSO alternator for about £600, to expensive for my liking. b) Ebay, britishparts, sng barret supposed Denso part for roughly £150. If go I with option b) will I get an alternator including a the regulator module or is this always an 'extra' item ?

I would be hacked off to order a new alternator only to find the regulator was really the issue or indeed vice-a-versa if the two items have to be ordered separately.

Regards
Neil

 

The modern alternators require a feed back circuit E.G. battery to produce current. The battery feed back determines the output of the alternator. Take the battery out of the circuit and alternator voltage goes to zero. The alternator comes as a complete unit iwth all controls internal. Before going that route let's try a few more tests.
1. After sitting overnight use a multi meter and measure the voltage on the battery at the battery terminals. Then measure the voltage at the battery cable connections.
Are you getting the same reading? If not remove the cables and clean the interior of the clamp and reinstall. Your overnight reading should be 12.6 to 12.8 volts.
2. If you have 12.6 to 12.8 then we can proceed to the next test. Start the engine and let it warm up. Then turn on the AC, headlights, radio, and windscreen heaters if equipped. This will place the maximum load on the system. Now using the meter again check the voltage at the post and connectors. you should now be iin the range of 13.6 to 14.5 volts. If you are in that range then there is nothing wrong with the charging circuit, if the battery voltage is beginning to drop then the alternator isn't keeping up. Now that leads to the next check.
3. If you now know the charging circuit is working then the most likely problem with the battery going flat or weak is a parasitic drain. Try the tests listed and report back what you find. If it is a parasitic drain I can give you the info needed to find it.

One other item to check and clean is the engine ground strap running from the engine to the chassis. It is located under the frame about a foot back from the right side tire. Corrosion there will affect the charging circuit.

 

Dang it Vern, posted just before me, so I cut my post down ...so +1 to Vern's post.
Your aspect is correct, the battery initially is simply to start the car and the alternator takes over and powers the car from there on and recharges the battery.
Have you checked on simply getting it rebuilt? Usually its a cheap voltage regulator that may simply need replacement, where a good shop will test and verify and bench test generally for much less.

 

Not a good procedure. NEVER disconnect the battery while the engine (the alternator) is running as this may result in the alternator producing high voltage spikes which can damage the car's electronics.

As advised by Vern, measure the voltage on the battery terminals (battery connected) while the engine is running. You can do this with everything off and everything on to see how the alternator copes. You should see 13.5 to 14 volts on the battery in both cases.

 

 

Here in the colonies, most towns larger than 100000 citizens have some guy (or more) that rebuilds starters and generators. When I had this problem, I tried to get the alternator out of the Jag -- bolts too tight/not strong enough/corroded in. Priced a replacement at my Indy, at my dealer, called the local rebuilder. He was five miles away: by the time my wife and I got back home in her Maxima, the rebuilder called to say the Jag was ready. $100 less than dealer or Indie, and price of a rebuilt unit at Advanced Auto (the chain for car parts). Solved all issues.

The rebuilder will replace the worn parts; turn or sand the armature; check all wiring, including the battery. And since almost all alternators today are from the same OEM suppliers, they are able to repair all cars.

 

You are right, I found the same procedure in my Jaguar Workshop Manual. To never disconnect the battery while the engine is running has been a general rule for all cars and this is the first time I see that it is allowed (in the case of Jaguar X308). Probably Jaguar electrical system has a built-in protection module that prevents the high voltage spikes from the alternator (when running without battery) from reaching any of the car electronics.

 

Finding a local rebuilder is always a good start -- next would be finding the OEM part number and getting a factory rebuild or new outside of the dealer network. In the USA most of the rebuilds are junk -- as are the Chinese clones.

 

If you buy a new alternator, it will be complete; bolt-on and plug-in. £150 at Barratt is a very good price as it is a genuine Denso, same as the £600 one but just without the "Jaguar" logo. You will notice that the part number for the 600 one is LNC1800AA (OE) and for the 150 one is LNC1800AA# (OEM). Without "#" means genuine part obtained from Jaguar; with "#" means obtained directly from the same manufacturer (Denso) who supplies to Jaguar. The only difference between the OE and OEM is probably less strict manufacturing quality control for the latter.

An option is to buy parts, the rectifier, regulator and the brushes and rebuild your old alternator. These are super easy to replace. I recently rebuilt my alternator with parts from "alternatorparts.com":
Rectifier: https://store.alternatorparts.com/in...ternators.aspx
Regulator: https://store.alternatorparts.com/in...regulator.aspx
Brushes: https://store.alternatorparts.com/pa...ternators.aspx
However, these parts will cost you about £130 including shipping to the UK.

 

 

Absolutely. You can keep the old (failed) alternator, rebuild it with the parts I mentioned in my earlier post and keep it as spare.