Hi Folks, I love this forum, so much good information. My wife purchased a 2004 Supercharged XJR with just under 88K miles from an online dealer. Everything has been great after some initial repairs (tires and a very bad tie rod.) Rides great, sounds good, shifts smooth, etc. We have put only a few hundred miles on it.

Earlier this week I replaced the dash wood trim panels. For safety I disconnected the negative terminal since I was working around the passenger airbag.

On our next drive, we drove a few miles and parked. When restarting the vehicle 30 minutes later, the shift from park to reverse was rough and we got a transmission fault. It shifted to drive fine, and drove fine the few miles home. We restarted and the light went off and all was fine as we took it for a 10-20 mile drive.

Yesterday we got in, and it did the same thing, Rough shift from park to reverse. My wife pulled it out of the garage and put it in park and turned it off. A few minutes later, she restarted and the same thing happened, rough shift to reverse and drive. We just put it back in the garage.

The battery is from 12/21 and seems fine. I disconnected it, cleaned the cables (they really didn't need it) and put it back on. On start it still had the fault and I waited for it to idle lower and put it in reverse, which was rough, so I just put it back into park and left it.

I also checked the transmission shifter cable (two bolts) as some have mentioned, but those appear to be fine.

It seems like the disconnect of the battery triggered this, but I'm not sure.

No trans dipstick that I can find to check.

Anything I can try, or do I take it to the local Jag dealer to get its codes pulled. IF that, do I drive it there, or have it towed?

Tkanks for any help!

 

Ok, some starting points...

1. Get the battery checked at Autozone or Advance or PepBoys...the random fails and rough idle just might be a dying battery. If you have trickle charger, hook it up overnight and see if errors go away. Also, if the existing battery is old style with caps that can be removed, make sure liquid/acid level is good in all 6 cells.
2. Retrace your route that you were working behind the dash panels. Make sure you did not accidentally disconnect or knock a key ground loose.
3. If you can get ahold of a cheap code scanner, check faults and fault code/description and post them here. There are some real sharp fellas who can point you in right direction depending on the fault code.

Keep asking questions when you learn more.

 

There is no transmission dip stick. Probably OK if no obvious leak underneath. I think there is an update for the transmission which may not have been done. An ATM reset and reflash would not hurt.

 

With 88K miles consider a transmission pan and filter replacement and a fluid change. We really can't help unless you can get the car scanned and report back what codes you find?

I think your OK to drive it to the dealer BUT be aware we have had reports of Jaguar dealers refusing to work on cars over 10 years old.
Might be worth a call before you drive down there?
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In fact, Jaguar dealer said just that, nothing older than 2012. Recommended a -place 2 hours away in another state. I have can tool in hand and will be diving in today. Thanks for the help!

 

Update and resolution (I think)

Based on ctsemicon's advice I hooked the battery up to my trickle charger. The light on charger went green sometime near to 24 hours. I charged it with the battery out of the jag, just to be really safe. I put the battery back in, and immediately started the car and saw the tans fault light still on, shifted to reverse which was hard with a lurch, then put it in park and shut it off. I then ordered the code scanner based on the advice from several of you here.

My code scanner arrived today and I dug in. First, I went down and started the car to back it out of garage. Immediately I noted the tans fault light was off. It shifted like butter and I backed it out and parked it. I think the battery had to be hooked up for awhile to do its thing.

Code scanner came back with TCM P1794: Battery supply malfunction.

Door module had a battery error too.

Plus a couple errors related to parking assist and rear sounder that are not battery related and that I will get to.

Searching that error I see things about corroded TCM connections, but this may just be bad battery given the door module battery error too. Time will tell. Given the approach of winter, I think I will replace the battery in the spring!

Thanks to ctsemicon, oldkarz, and clubairth1 for your help.

On to the next bug after a fun drive!

 

You might consider replacing the battery, sooner than later.

 

Just a note on corroded TCM connections?
Don't ignore that because the 6 speed ZF is famous for a leaking sealing sleeve at the TCM (Actually ZF calls this "Mechatronic") connection.
Have you inspected this? It's the large wiring connection on the back of the transmission up high. It's the only electrical connection to the transmission. Make sure it's dry with no transmission fluid present.

But I found this thread and it points to something different? Code P1794
They mention an auxiliary battery that is mounted inside a module behind the glove box? Now this is a LR and NOT a Jaguar but same company.
LR Error P1794

That maybe in error as I found this definition of the code?




Here is the entire thread and I think you need to remove the TCM plug at the transmission and make some measurements?
Gearbox Fault

Of course if things are working just ignore it for now?
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Glad to see your making great progress!..some additional notes;

1. It is always a best practice to short the red/hot/positive lead to a ground when disconnecting battery. After you disconnect the positive lead, wait about 10 minutes, then touch the positive lead (the cable, not the battery) to a known good ground in the trunk for a few seconds. I have never researched to understand why, but I find discharging any possible residual energy (capacitors?) in electrical system seems to prevent spurious faults when reconnecting.

2. You will find numerous threads on a appropriate battery for the XJ8/X350 forum. I have a personal opinion that if cost is no object, the Bosch AGM seems to work best. However, its hard to find and I have had excellent luck with the Duracell AGM that Sam's Club sells. But there are as many opinions as there are batteries. Any good, AGM Group 49, preferably sealed not the open cap type will get you 3 years plus.

Best of luck, enjoy the car, they are they last of a dying breed.

 

Thanks again everyone. I'm peeling the onion on this one!

Last nights drive threw the transmission fault for low battery and the car didn't want to shift to 4 or something.

Decided to acquire the new battery today after some more spurious faults

New battery in place and hooked up scan tool to check codes from night before. Saw an existing fault that said right rear brake light is shorted to battery, as well as the TCM battery one. Started it up and tested all the lights. Everything working. Cleared codes and took a drive. Got the same fault and read the codes:

TCM fault for low battery (P1794 Battery Supply Malfunction.
Drivers door module low battery
Saw an intermittent fault too, where the high beams would not switch on, but then did a minute later when we tried again

Sounds like an electrical issue? Ran the scanner as wife drove and monitored voltage, it stayed in the 14-15 range.

Quick poke under the dash to Investigate the TCM, didn't see any obvious moisture. Haven't pulled the connector yet to check for corrosion (to late in the day for me lol)

Those three errors seem to point to some sort of bad connection or wires crossing. Anyone ever see this type of thing before.

 

When doing any battery disconnect, you need to reset the car's computers and modules, which continue to store some faults and other information for a bit until their internal electrical storage is discharged. You need to short the Positive and Negative cables together for several seconds, or maybe even a few minutes. This performs a hard reset of the various modules. Then the cables can be reconnected to the battery. This process cures many mysterious problems.

 

Took it to a somewhat local place (45 minutes away.) The found rodent damage on some wires and fixed that as well as disconnected and reconnected a bunch of connectors. Things works great now.

 

Any chance you can tell where the damage was? Maybe help point someone else in the right direction?
Lot's of time that occurs because the car has been stored for some time.
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