Jaguar XF 3.0d Project part 3

Published on 1 March 2024 at 15:31

Well it was still raining today but fortunately Russell had put the Lotus Cortina up on the lift so I was able to back the Jag in and work in comfort. To cut a  long story short I had worked out that the battery monitor module was not talking to the rear body control module - BCM. It talks with something called LIN Bus, which uses a single wire - white in this case. I had found out that the wire went  up in to the boot lid, which is  a  common place for these breaking so that's where I thought my problem would be. The plan was to gain access to the bcm by removing all the panels and covers and then jumping the cable directly so it didn't go through the boot loom any more. When I got in there  though things quickly took a sinister turn. The first thing I noticed  is that the plastic casing was broken - never a good sign. Closer inspection showed there to be  green corrosion on some of the connectors, most notably the two on the bottom. When I removed those two I could see the problem instantly, the pin for the LIN bus connection was bent right  over, somebody had definitely been in there before and been clumsy. Sadly the pin snapped off when I tried to straighten  it as they often do. I had to remove the whole thing, take it apart  and solder a wire on the the back of the printed circuit board. I then drilled a hole, fed the wire through and soldered it to the wire going to the plug.

It sounds fairly  involved but the whole job took less than an hour and a half and my BMS error has now gone - the job was a good un. The good thing about this is that while you can buy a replacement used  one for a couple  of hundred quid it would need  to be programmed to the car's ecu, by repairing the old one that was not needed. I understand a  main dealer would charge about 1200  quid for this job so my little bit of wire wins in every way.

I was able to fix the plastic casing with a plastic welding kit, a great addition to any workshop, I have one at home that is mains driven but this one was rechargeable and did a great job.

Once done I hooked up my diagnostic box, reset the monitor and told it I had a new battery. Instantly the alternator voltage to battery went up to 14.8 volts, which confirmed that everything is now working. When the monitor does not report back the ecu sets the alternator to a default voltage of 13.8 and switches off the heaviest current drawing devices eg the seat heaters and the pre heater, I think it disables the heated front screen too, all those things now work.

So next job is  disabling the keyless  entry, I have no problem pressing a button to get in the car and I don't want somebody stealing it. I also have to install the tracker, useful if somebody does manage to nick  it and also if I forget where I have parked it. Again.

OOO almost forgot, the entertainment system  reset itself a couple of times and I notice it won't tune any DAB stations. This is almost certainly down to the DAB  module that lives beneath the passenger seat, where it gets nice and moist. When they play  up they break the MOST fibre optic circuit and the system shuts down. I am not too fussed on DAB, we don't get many  stations out here, when I listen to radio it's nearly always GHR, which I get on FM - it's better quality than DAB thanks to Tony sodding Blair's greed in going for the maximum number of licences rather than the best quality. I could bung a new module in there at a cost of just under 400 quid but I think a £6.50 bypass cable is the better option.

MoT is booked for next week, I am still trying to find out if the cam belt was done, it looks so well maintained that I can't believe it wasn't and I am pretty sure the original would have failed by now but I just can't take the risk. That will be a big bill but as I paid the right money for the car I can live with it.

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