OBDII wiring, fuse & relay

[ptjs1]

I wonder if anyone can help me with a problem I have on my 1997 RHD XJ8 4.0 Sovereign.

The OBDII port has not functioned in the 5 years that I've had the car. My dealer is not able to interface to it and when I plug in my Bluetooth module, it doesn't even indicate the power light.

I have wondered if there's a break in one or more of the wires through chafing. However, it's extremely difficult to access any slack on the wires to the plug without taking out the scuttle panels and centre console.

Today, I wiggled the plug and could hear a clicking sound behind me when the plug wires were moved. On closer scrutiny, I tracked the sound down to a brown relay in the RH heelboard fuse and relay panel.

The problem is that I don't know what is this relay and also which is the correct fuse(s) for the system. Because I have a very early 1997 car, Jaguar didn't seem to have any owners handbooks for the new XJ8 and the car was supplied new with an x300 handbook!

Captains Jaguar cathouse diagrams are hard to track down these days but the 2000 MY diagram seems to indicate that the fuse is in the LH heelboard not the RH heelboard. I don't know if 1997 cars are different.

So, I'd be very grateful if anyone knows:

-What is the correct fuse (or fuses) that control the OBDII plug?
- Is the brown relay in the RH heelboard also controlling the power supply?
- Does anyone know the pinout of the OBDII plug, in particular which are the direct and ignition-controlled pins + also the earth pins? I could then run independent power and earth wires to these pins to eliminate any issues that might exist with these wires.

Tks for any suggestions

Paul

[ptjs1]

Well, I just checked that LH fuseboard and there was no fuse in position 4 which the 2000MY diagram indicated was the OBDII fuse. So I put a 5a fuse in and it immediately sparked and blew as I pressed it in.

So I guess that might indicate that the power wire is grounding out somewhere between the fuse and the plug?

If I now knew the pinout of the plug, I suppose I could run a (fused) wire direct from the battery side of that fuse junction direct to the OBDII plug and see if that solves my issue?

Paul

[ptjs1]

Sadly no responses here, but I managed to get the info I needed and a wiring diagram via another Jaguar website forum.

Well after 4 days effort it's finally sorted!

I had established that without the ignition on, the brown auxiliary circuit relay clicked every time I wiggled the OBDII plug. Also, the direct battery feed fuse blew every time I put a fuse in. So, an inadverted earthing of the live circuit on wire 16 seemed likely.

Lying upside down in the drivers footwell, I quickly realised that Jaguar had tried to minimise the wire lengths and I would be unable to access more than the last 2 inches of wires leading to the plug. However, I could just see that a number of the wires had chafed about 6 inches back (there are a lot of sharp bare metal edges down there!).

It seemed that the only way I could realistically access the chafed area would be to take out the aircon controls, the radio, and unfortunately the whole of the centre console. I could then try and thread the OBDII plug back into the area behind the radio and try to sort the chafed wires from there.

All of the above eventually came out and then I did something that no owner should ever do! I unbolted the bracket that holds the OBDII plug to the outside of the forwrad part of the transmission tunnel. Big mistake! The bracket is attached on the inside of a tubular bracket that is bolted to the transmission tunnel and which seems to provide support to the whole of the dash. As the bolt came out, the tubular bracket dropped 1" and I knew straight away this was going to be a complete pain to get back in place.

I carefully cut free some of the ties around the loom and now managed to wiggle the OBDII plug back behind the radio recess. It still wasn't easy but I could just reach the chafed wires. I separated the wires with small strips of rubber between them and then put a new fuse in #4 in the LH heeelboard and connected the battery. The fuse didn't blow! I then connected my Bluetooth OBDII module and it lit up! I started the car, launched the app on my smartphone and Bingo! All the readouts were working andIi could scan for fault codes (although because the battery had been disconnected, it didn't find any!) I did notice that one of the lambda sensors was almost flatlining without the expected fluctuations when I blipped the throttle. So, I'll need to check that out.

I then carefully (and with difficulty!) put some small strips of insulating tape around the chafed wires, threaded the plug back to its mounting point, checked it was still working and started the reassembly of the car. It took me a whole day (Yes!) to get that tubular bracket lined back up with the captive nut. Everything else was ok.

So, after 4 days I now have my OBDII plug working. 4 days to put a bit of tape around a few wires! Don't you just love the x308?!

Paul

[J44EAG]

I thought you had a bad back! I know what that is like but in the end you JUST HAVE TO TRY TO FIX IT. Then you feel satisfied!

Well done, Paul. Nasty job and not the type of work I enjoy. Hats off to all those who are able to do some of this extremely fiddly and inaccessible work. It always worries me that if I make a mistake with car electrics and electronics, I might make things worse and bring the the car to a permanent halt.

I have a car that has lost the -Ve ground feed to the cigarette lighter. Probably just the connector on the unit but how on earth does it come to bits?

Failed electrics fill me with horror. The amount of dismantling can become quite daunting. Off with the bumper to gain access to the heater valve....

Nice one, Paul.

Mike

[ptjs1]

Tks Mike!

Yes, I am between back operations, but it's amazing how you can seem to shut out the pain when you're focused on achieving something mechanical that requires a lot of thought and concentration. I was dosed up on painkillers every 4 hours and lay in a hot bath twice a day during this work.

The one good thing about the x308 compared to the x350 is that you can get the drivers seat to recline right back. With a pillow on the floor of the footwell to support my head, lying upside down put me in such a contortion that every bit of me hurt as much as my back!

I've got pretty slim hands but even so they are now covered in cuts and scabs! The amount of sharp metal around that dash frame is lethal! I did take care to wipe all the blood off the interior as I went along!

Working on anything behind the dash does make you realise the enormous electrical complexity of modern cars. With the huge fuseboards open behind the heelboards and in the boot, it did make me think back nostalgically to the 4-fuse holder in the 1968 mini that I learnt to drive in! I do wonder if a complete reshell and rebuild of such a car as the x308 will ever be an economically viable proposition?

Paul