Hi All,
1998 3.2 sport, low mileage and used as a ' weekend ' car. I started it a couple of dags ago and noticdd the light and dashboard lights flickering. After a couple of minutes the dash display reported gearbox and stability faults. The gearbox gave a very hard thump when I put it into reverse. I switched off and today fully charged the newish quality battery. This time the lights would not come on. I had originally thought it may be alternator but now think it is an ecu issue?

 

It may be a weak battery or perhaps the instrument cluster is failing? The cluster is part of the CAN communication buss and if the buss is not communicating correctly, you'll get a number of reported failures. These cars are very sensitive to battery voltage so I'd start with that check...

 

Dear David,
thanks for your reply. I too suspected battery, athough it's about 12 months old and regularly charged with my c-tek charger. I charged it fully before starting today on the indacted fully charged battery when I got all of the faults, so as you suggest it may be instrument cluster related. The very hard lurch going into reverse and the gearbox fault warning is odd however.

 

Did you check the voltage on the battery terminals while the engine is running?

Otherwise, low alternator (and battery) voltage often causes false gearbox faults to be desplayed, hard shifts and restricted performance.

 

Dear M. Stojanovic,

Thanks for your reply, I will take it into my local garage for testing. They are backed up at present with work, so it we be a couple of weeks or so I think before they have the time to get to it. I was hoping for an easy fix!

 

Perhaps you can just buy a multimeter (£10-20) and check the voltage yourself. Very easy, takes a few minutes.

 

Yes, of course! will do this later today.
Many thanks!!

 

While the battery could be perfect, the ground connection may not be. It is a good idea to
check the ground connection just to remove that from the suspect list.

 

Please find and read ALL TSBs related to your car.
Many issues have been noted by Jaguar and possible solutions given.
This TSB may or may not help.

 

Hi Randy S.
Thanks for that advice, I checked the earth strap and it does appear to be secure. Further to the advice to measure the voltage to the battery with a multimeter, static it measured 12.1v and running 13.4v but surging to 15.3v momentarily with a drop in engine revs, which to my mind suggests a failing alternator?

 

12.1 static voltage means that the battery is at about 50% charge. You should immediately fully charge it to prevent its sulfation (loss of capacity).

The fluctuation of the alternator voltage may not mean there is something wrong with it. I had similar fluctuation on my car once and found that it was caused by deteriorated crimp of the battery positive terminal to the cable (the one that runs from the battery to the "megafuses" in front of the spare tyre). The crimp looked fine on the outside but it was not good inside. I diagnosed this when I found out that the section of the positive cable near the battery terminal was rather hot after just a few minutes of car idling.

It appears that a poor contact in the crimp (causing some sparking inside) causes the current flow into the battery to rapidly fluctuate which confuses the alternator and causes it to excessively fluctuate its output. I suggest you first check whether any of your battery cables (positive or ground) is getting warm/hot near connections to its terminals. If yes, you will need to replace that cable. Battery cable crimps looking good on the outside but bad inside seems to be a fairly common problem on our cars. I made new positive and negative cables myself - I bought a length of heavy gauge cable (100% copper), suitable cable terminals and a hydraulic crimping tool (you need hydraulic because of the size of the terminals). Never had flickering again. Perhaps you can find a shop which can make these cables (they are not cheep as Jaguar parts).

In addition to checkig the temperature of the cables, you should also open the"megafuse" box, undo the nuts, clean well all connecting surfaces (cable terminals to the fuses) and reinstall. Be careful not to overtighten the nuts. Also check the engine ground strap connections. Only if the cleaning of connections and replacing the battery cables (if found to have poor crimps) does not solve the problem, then you can suspect the alternator. If you determine it is the alternator, you may need to only replace its Voltage Regulator which is not too expensive and is very esy to do.

 

Dear M.Stojanovic,

Many thanks, that is very useful information!!

 

The first step when you run into any electrical glitch in these cars is to do a hard reset. Remove the negative cable from the battery, touch it against the positive terminal for 10 seconds, then reconnect it to the battery. Sometimes it's just that simple. Many times, actually. Try that first before moving on to the other suggestions.

 

Thanks for that tip re the hard reset. Have charged battery and tested again with multimeter. Shows 12.6v at battery but ranging voltage when running from 13.1v to 15.7v with intermittent drops in tickover engine speed as if alternator is tripping on and off with accompanying strange noises. Local garage booked up at present, they suspect alternator problem. Will update when problem identified and rectified.

 

15.7V is over voltage. Broken alternator may whine strangely when putting high voltage out. Voltage is high but current is low.

 

Yes, I do think the alternator is the problem. Dealer installed new 'engine pack' at 47k (nikasil issue) current mileage 110,000 but expect that original ancillaries refitted.

 

would you be able to take a photo of the cable to the mega fuse box that you have done the repair on thanks again!

 

Remove the two trunk and battery floor panels/covers. Remove the spare tire. You will see clearly the black box that has the battery positive cable going to it. Remove the covering to the box and there’s 3 megafuses inside. Not only can the positive battery cable get hot and fail but, so can the negative cable as well. *Carefully* snug the megafuse nuts as I’ve seen them loosen up over time. If it looks like something has melted, it’s likely the battery needs to be disconnected, remove the megafuse box assembly, disassemble the fuse from the box and see if there’s any signs of discoloration as overheating causes that. Clean, tighten the nuts and reinstall the black box in the spare tire well.