ok jag lovers.....lets get this sorted once and for all!!.......I have a problem.....ive read forums around the globe and many people have a similar problem........but no one has bothered to post a fix........


There are several jag heros on here that give loads of advice,...massive thanks to them......lets see if WE can post a proper solution to the dreaded ...P1797!!


is it the buscan wires......is it the neutral switch.......is it the internals of the merc box.........ive had all of these from jag dealers!!....so which is it??


My woes are on here and other forums to read...in a nut shell, she throws up the code....most of the time she drives fine even when shes showing the problems on the dash.......the dash goes mad with stability fault, gear box fault, hand brake fault, ABS fault and the needles drop for 6 seconds then goes right again.......every 2 mins or not for a week......sometimes the box goes into spasm.......slips, jumps through the gears and is undrivable.... a restart fixes it for a bit...some times..SO WHAT THE HECK IS IT GUYS!!!!!...if its a component such as ECU, TCU, J GATE, ABS unit etc. I can swap them for parts from ebay and if no better re sell them......if its a buscan wiring fault can I simply slip in a pair of wires between the box, TCU, ECU etc.........come on guys...some one must know the fix to this dam fault......there's a bottle of good scotch in it for you and im not joking!!!!!!!!

 

Could you give us some background on the car? Has the engine or trans been out at any time?

It *seems* like you may have a faulty connector or connection...... does it happen on cold/hot days in moisture or when dry?

Try disconnecting and reconnecting the harness plugs one at a time starting at the engine bay... Also, have you double checked the bulkhead connection?

Since it is throwing multiple codes, it would be logical to think that it is a connector that is associated with ABS etc.

We'll get er done, just a matter of time.

 

Unfortunatelly, there is no straight answer to your question. The ONLY way to fix her, is going by the process of elimination. Start at the simple one, and progress from there. EVERY problem has several possible fixes, and only by eliminating them one by one, you will find the right fix.

The main thing is,.....understand the code, figure out WHAT can throw it (multiple sources), don't cut corners, don't rush, and you WILL find the solution.

Of course, we'll help as much as we can over the keyboard.

 

unfortunately she's out of MOT at the mo....and the little darling that had her in to diagnose the fault also tested her and failed her due to the ABS light coming on.....even though he knew dam well there's no fault with the braking system......what is it they say about dark alleys and no witnesses!!......
I bought her cheap from ebay (ok....alarm bells rung with me too)...she drove great on the hour test....but as I hit the motorway the amber gearbox fault light showed and she was stuck in 4th (?) for 200 miles......the fault cleared at the petrol station and didn't show again for 200 miles over a week.......the seller said it had popped up a few times before he had parked her up for 6 months.....that battery has been tested and shows good...........the indi I took her too said his jag scanner only showed a dash board fault so I got another XJR unit and the dash madness continued.........but as she's out of test I've not had her on the road since...need to change the rear sub frame mounts....Im clutching at thin air here to find the fault as P1797 seams to have different meanings depending where/who you talk too including jag dealers!!

 

Since you're in England, I would start with ALL the grounds (inspect for corrosion, clean, reconnect), then,.....as Snyder suggested, all the electrical connectors (inspect, clean, spray with contact spray, reconnect). This should keep you busy for a while!

After every "round" is completed, do the "hard reset", test drive, and continue. Document everything you've done, and post it here. Between all the brains we have here, I am confident we can figure it out.

It's just a car after all. Finicky, and temperamental (like all felines!), but NOT smarter then the collective brain power available on this forum.

 

Has the engine bay been "cleaned"; as in the detail shop turned on the pressure washer to give you a "Clean" Jag ?
even though the battery "tested" good how old is it?
Next would be to trace the harness and check connectors

 

I agree with MyTurn. This is where I would start as well.

Even though it isn't the cheapest starting point, I would change the battery first. They don't last long if they just sit.

 

I can understand you're exasperated but....you've had the fault over a year? can you confirm how the car behaves?

You might as well drive a Porsche into a Jag dealer's with this model, it's ancient to them! A more likely answer is to find a bloody good Jag indy in your neck of the woods, there's a few in Yorkshire! It can be any number of things from the TCM, connections, wiring, ECM.
Battery has been known to trigger this when it's about to expire.

You're trying to get it MOT'd?

 

generally she drove spot on even with the dash board going silly with all the faults showing up, but when I had it to the Indi at Harrogate she drove like a pig, stutters and jumps, then felt like the box was slipping, I pulled over and restarted her and back to normal!........this comes and goes but until I can get an MOT on her im a bit restricted as to what I can do.
Ive just got a spare j gate unit to swap on to see if that makes any difference....

 

I copied P1797 DTC summary information into this JPEG file:
https://www.dropbox.com/s/t1ghgwmgs8...n%20WA-580.jpg

Here is a list of P1797 issues threads (10 of them) with their weblinks and posts (that point to the fault and possible resolutions):

https://www.jaguarforums.com/forum/x...unction-40136/
post# 10

https://www.jaguarforums.com/forum/x...-button-96323/
post# 6

https://www.jaguarforums.com/forum/x...esolved-70570/
post# 1 & #4

https://www.jaguarforums.com/forum/x...es-help-79945/
post# 3

https://www.jaguarforums.com/forum/x...p-codes-73087/
post# 7

https://www.jaguarforums.com/forum/x...t-codes-72181/
post# 1

https://www.jaguarforums.com/forum/x...-please-58419/
post# 8

https://www.jaguarforums.com/forum/x...ed-help-41080/
post# 2

https://www.jaguarforums.com/forum/x...ng-fine-37088/
post# 2

https://www.jaguarforums.com/forum/x...-99-xjr-29774/
post# 2

https://www.jaguarforums.com/forum/x...ii-codes-2912/
post# 2

Jim Lombardi

 

In my thread above ('97 XK8 gearbox fault codes ) I incorrectly attributed the problem to the TCM. It was actually caused by the Ultragauge not being forced to run with 9141 protocol. When I swapped the TCM I unplugged the Ultragauge to Use the AE software and forgot to plug it back in.