[R6UEN]

For the last month or two my XF has been juddering when pulling away. It didn't feel like an engine misfire, but more like the transmission slipping. At first I wondered if the wheels were spinning up - it seemed worse when the roads were wet or accelerating hard. I booked it in for a diagnostics check and had a two week wait. Of course, as soon as it was booked the juddering went away. I naively hoped the car had sorted itself out and so I cancelled the check and...yep, a few days later it returned. By now we were booked on the Le Shuttle to go to Bruges for a few days. I'd missed my diagnostics slot so I thought I'd chance it.

Needless to say, within minutes of the car consuming French air, the juddering returned and worse, the ABS warning light came on, so did the power steering light. In fact, every warning light & message you can think of. Now I wasn't unduly worried as this Christmas tree effect had happened before and was cured by turning the engine off and leaving the car for a few minutes. This worked again although the juddering remained. What's more I found the juddering seemed to occur when cruising at certain speeds and not just accelerating.

As we drove along my wife mentioned the stop-start had stopped starting...or stopping some months back. In the recesses of my mind I remembered reading in the forum about voltage drop in old batteries causing issues. Armed with a Belgian beer in the hotel, I smurfed the forum and reading the posts decided a new battery was needed - it was six years old after all.

This afternoon I have just installed a new battery and the car is transformed. No juddering - whether accelerating hard or cruising at 'those' speeds. I now realise this was the gearbox changing up & down at the wrong points. In particular it couldn't decide which gear to be in cruising at certain speed and would change up and down. I'd verified this by following a forum suggestion and manually changing up or down.

I brought an iCarSoft justifying it to my wife that a diagnostic check costs. It verified that the old battery was running at 11.97; the new one is 14.7v. There were numerous fault codes - the majority were historical data - so I cleared them all and took the car for a nice run. All remained cleared so I'm a happy bunny.

Thanks for all the posters in the forum on battery issues & replacement, they were very useful. And let me pass on two tips which I don't recall reading but catch me out when replacing the battery:

• Don't forget to set your Jaguar Remote App to "service". I didn't, disconnected the black terminal and within a minute my iWatch and iPhone were buzzing me to say the car was being tempered/stolen.
• I rang the InControl people to say "it's only me" except they couldn't trace the car via the registration plate. I'd failed to update the registration in the App when I put the private plate on and I couldn't recall the original plate.

 

[OBC John]

A story with a happy ending! Nice one.

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[FCS]

The info on here about battery issues is probably what has saved people the most money. XF's need the volts all of the time, not just to start. Glad you got it sorted.

 

[Gav]

I can only assume that a drop in volts causes the modules to behave unpredictably, and need rebooted as when the car is started the alternator will provide the power most of the time and this will be higher than the battery voltage.

 

[FCS]

I can only assume that a drop in volts causes the modules to behave unpredictably, and need rebooted as when the car is started the alternator will provide the power most of the time and this will be higher than the battery voltage.

I suppose it depends what is wrong with the battery. A shorted cell or shorted when hot would cause havoc with the charging system. Volts may then pulse up and down. I suppose a bad connection to the battery could also do it.

 

[R6UEN]

I agree about the alternator providing the supply at higher speeds. As it is, the juddering has returned, albeit not as bad as before. Definitely improved at lower speeds and now very smooth when crawling in traffic (perhaps when current is being drawn from the battery). So my elation is somewhat premature. The stop-start is really working well after 12 months - again at low speeds when the battery is involved.

I checked the codes and two faults show. One is the self-parking (which I've used only half a dozen times in 6 years) and the immobiliser. I suppose the latter could be failing intermittently, but thought that would feel like the engine mis-firing rather than transmission slipping. Besides don't immobilisers just work or not? The investigation continues...

 

[MalcXFR]

The stop-start is really working well after 12 months - again at low speeds when the battery is involved.

I'm glad this isn't at high speed

 

[Gav]

I agree about the alternator providing the supply at higher speeds. As it is, the juddering has returned, albeit not as bad as before. Definitely improved at lower speeds and now very smooth when crawling in traffic (perhaps when current is being drawn from the battery). So my elation is somewhat premature. The stop-start is really working well after 12 months - again at low speeds when the battery is involved.

I checked the codes and two faults show. One is the self-parking (which I've used only half a dozen times in 6 years) and the immobiliser. I suppose the latter could be failing intermittently, but thought that would feel like the engine mis-firing rather than transmission slipping. Besides don't immobilisers just work or not? The investigation continues...

The alternator will supply power as soon as the engine is started, not only at high speed.

 

[wilf]

......but maybe not enough for the full electrical load - it will need some revs to do that.

 

[Gav]

......but maybe not enough for the full electrical load - it will need some revs to do that.

Modern alternators will produce 30+A at idle and as much as 125A at 1250rpm or so enough at idle..

 

[OBC John]

Modern alternators will produce 30+A at idle and as much as 125A at 1250rpm or so enough at idle..

Yes, I'd be surprised if it's designed so you can drain your battery while idling.

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[cutlea01]

When was the gearbox last serviced? Although Jaguar say it's sealed for life, it isn't. Unless you consider it's life to be 80,000 miles. Maybe you need a fluid change (NOT flush).

 

[R6UEN]

Now that's something I hadn't realised. Cheers