Gearbox Fault, Parking Brake Fault & Cruise Unavailable

[agbrowne]

I thought that I'd explain a problem that I've just had with my 2007 XJR Portfolio...

The symptoms were initially as the title of this thread, but gradually deteriorated to the point where the car wouldn't start at all. I also got some pretty crazy, unrelated faults, such as when the temperature gauge went down to zero, the high temp warning light came on and the cooling fan started up at maximum speed! For those who have any knowledge of these cars, they will probably immediately be thinking along the lines of a CANBUS problem... Well, the CANBUS was receiving false data, but there wasn't a problem with the CANBUS itself as you will see if you read on.

It all started when I drove the car out of the drive a couple of days after a drive down from Edinburgh. As soon as the car started moving, the yellow brake warning indicator came on, the orange "lozenge" warning light came on, the messages in the title of this thread were displayed and the car refused to move any further. I switched off, waited a few seconds, then re-started it. All the warnings disappeared and the car appeared to drive normally for a while.

Then the problems started...

The drive became very jerky, almost as though the gearbox was slamming in and out of gear and randomly changing gear. The warnings re-appeared and at one point, the car decided to randomly apply the handbrake. Luckily I was travelling quite slowly at the time, so I gently drove it home, trying to keep up as constant a speed as possible so as not to damage the transmission.

Following a lengthy call to Rob Jenner (Thanks Rob), we came to the conclusion that it might be one of the following:-

1. Battery.
2. A break in one of the CANBUS connectors under the transmission tunnel cover.
3. The under bonnet earth points.

To address No1, I replaced the battery with a fully charged good one (I have two good batteries -- Long story but that's another subject) but the problem was still there.

To address No2, out came the transmission tunnel cover, the display unit/radio and the J-Gate. A thorough inspection of all the wires and connectors revealed nothing and the problem was still there.

There are three under bonnet earth points which are sometimes prone to corrosion. To get to them, remove the bonnet slam panel and you will see them along the front of the upper cross-member, behind the headlights. Two on the left and one on the right. They have been known to corrode and even to break off. If the latter happens, then they need to be re-made, preferably with aluminium bolts. If you use bolts made of any other material, then galvanic corrosion will start and eventually, they will go bad again. Assuming that the earth points are intact, clean them up and re-make them. Do not, repeat NOT apply copper grease to them! If you do, they will corrode very rapidly indeed! I just cleaned mine up and re-assembled them dry. Also do not swing off the spanner. If you do, they will break. According to Jaguar, they should be tightened to no more than 6nm. In other word, just nip them up. Cleaning these earth points also had no effect on this fault.

A couple of days later, I tried again, only to find that the fault had got so bad that the car wouldn't even start. After thinking about it in depth, and another phone call to Rob, I concluded that the car didn't know what gear it was in and was possibly "thinking" that it wasn't in park. By this time, I had various audible warnings going off at random times such as the parking sensors, and the "out of park" warning, even though the lever was in park.

I had recently had the gearbox oil and filter changed, plus the connector sleeve. I strongly suspected that the problem was down to the gearbox connector, which was impossible to get to unless the car was on a ramp. For reference, the connector is at the rear of the gearbox, on the right hand side and tucked away up above the rear gearbox mounting.

I spoke to Barny Jones, of Barny Jones Jaguar, who is an independent Jag mechanic near Farnham. He thought that it might be the J-Gate at fault and agreed to lend me a replacement. this was duly fitted, but to no avail.

I got the car recovered to Barny's garage, which required me to get it out of park manually. For those of you who don't know how to do this (which is probably most of you), there is a small two-sided cam which looks a little like a tiny butterfly nut, on the passenger side of the J-Gate housing. To get to this, you prise off the J-Gate surround trim, insert a screwdriver down the side of the J-Gate, in front of the cam and keeping the screwdriver upright, push it rearwards. This takes a bit of practice, but once you get the hang of it, the park lock will release and you can move the gear lever. Obviously, take steps to ensure that the car isnt going to run away when you do this. Either chock the wheels or ensure that the handbrake is applied. Cover the footbrake as well, remembering that there might not be any power assistance!

Barny changed the gearbox oil once again and whilst the pan was off, checked all the electrical connectors, finding them to be in order. The car then started and ran whilst he refilled the gearbox. With the engine running, he happened to move the gearbox connector loom and the engine suddenly stopped and the faults returned.

After some diagnosis, there was found to be no 12v feed to the gearbox. Together, we tried to trace the loom, removing the cabin air intake to get at the gearbox loom connector and the engine ECU connectors. These were all found to be clean, dry and in good order. The gearbox loom connector was duly opened up and continuity checked between it and both the gearbox and the under bonnet fuse box. A break was found between the connector and the fuse box.

The loom in question comes from the fuse box and routes round the back of the engine bay. Rather than dismantle the entire rear of the engine bay, which would have taken ages and cost me a fortune in labour, we agreed that the best fix was to run a new wire from the fuse box to the gearbox loom connector, bypassing the break. This enabled the gearbox ECU (or TCM) to power up and start talking to the CANBUS again. the car then started and ran perfectly.

The problem was that with the TCM not powered up, the car had no idea what gear it was in or what the transmission was doing, hence all the faults and weird unrelated errors. Once 12v was applied to the TCM again, everything went back to normal. I'm going to keep an eye on it all because I realise that the damage might not be restricted to the 12v power lead in whatever connector there is, buried in the depths of the rear of the engine bay, but for now, its fine. If I ever have cause to dismantle the rear of the engine bay for any other reason, I'll fix the connector properly and remove the "rabbit-run" wire.

[J44EAG]

I assume that is you, Alistair?

Thank you for the heads up on this fault. These complex repairs can be a nightmare with just one fault causing masses of issues and the possibility of many hours of diagnostic work. What to say? We just have to keep at it with these now aging cars.

Mike

[Norbertflyer]

Had the same symptoms, Gearbox fault, ABS not available, cruise control disabled. OBD2 Bluetooth car scanner app suggested speed connection to rear right wheel fault. Took wheel off, released the connector and squirted a bit of Halfords electrical contacts cleaner in. Reset the connector a few times and cleared the fault codes. Drove it round the block. All sorted. Richard