OK so as you all know i have been plaged with electrical problems on my 98 xj8l vanden plas. I got everything fixed except the issue with driver window and moonroof, all the wires look good, brand new battery, all grounds and power cleaned. Nothing helps but a hard reboot and then it only works for a day or so. What should i try next? Driver door computer? Im ag a loss.

Thank you in advance for and help!

 

Take the door trim panel off & check if the power is actually getting to the window motor when you press the window switches. If there's voltage at the motor but the window isn't moving, then the motor has failed.

If you are not getting any power at the motor, then it could be any number of things & you'd need to fault-find with a multimeter & work backwards until you find the point where the power is not present.

it could be the door module, it could be the fuse & relay-or it could be that the wires in the flexible rubber tubing between the door & the main vehicle chassis have fractured internally after many years of opening & closing the doors. It may also be corrosion on the electrical connectors inside the door-any water leaks into the door can cause corrosion to the electrical parts.

Electrical faults usually take time & methodical tracing to find the cause-although sometimes you can get lucky by replacing parts with guesswork

 

I believe its the door computer because a hard reboot fixes it for a bit. I can roll up and down the window lots of times and its fine. After its been parked for a while i start it up and the window and Moonroof go out. The local jag dealer told me based on his 30 years of jag service its probably the door computer. He said for 120 he can scan that computer and see what it says.

 

It depends whether you want to spend 120, or check the connections first inside the door itself to see if there's any obvious fault such as corroded connectors etc. If the wiring or connectors are faulty then a new door computer won't fix the fault.

There are 2 ways to fix electrical faults:

1) Replace modules & wiring looms until the fault is cured (expensive)

2) Methodically check the voltages at various points on the car using the circuit diagrams (much cheaper but much more time consuming)

My own personal preference is to start ripping everything apart & do the electrical checks myself, rather than pay someone to scan things & tell me what I could have found out anyway from the electrical checks with a multimeter.

For something like door switches & power motors, checking with a multimeter can trace the fault just as well as scanning devices. I leave scanning for faults for things like engine management, where scanners are more essential because of the huge amount of fault codes that can be thrown up for OBDII etc.

But for a door window not working, I'd be ripping the door panel off & measuring things inside the door with my trusty circuit diagrams on the seat next to me

 

I took the door apart already. Computer and plus look great, no corrosion rust or anything. When this happens the door computer clicks like its trying to power the window but no power to window motor. All the wiring looks good also. The computer controls the entire door, and i don't have a key fob so it could be a fault with the latch assembly too. Idk

 

Jamie:
If the module "clicks", then it should be a simple matter, using the schematics, to work through the motor power circuit. It is hard to explain how a hard boot would affect this problem. Maybe you just have a coincidence and not a cause and effect relationship?

Do you have the schematic printed, and do you need help stepping through the circuit with your multimeter?

 

There's only 2 wires to the window motor, so it should be easy to monitor the actual voltage there with a multimeter & see if power is present

 

The motor is for sure not getting power. Also when this happens the Moonroof messes up also. I open it and it closes a few seconds later on its own. From previous post the two issues are related somehow.

 

Well, if the sliding roof and the window function are related, it would be a signal from the Security Module through the SCP network to the BPM and then to the two control modules. I doubt that a flakey network by itself would cause the roof to open, so I assume it would be one of the modules. It would be worth trying to GENTLY heat the BPM and the SCLM modules individually with a heat gun to cause the case temperature to rise about 25 to 30 (F) degrees and see if you can "force" the problem.
My gut feelingis that it is likely the security module thinking that the "all lock" signal has been commanded. I bought a security module on ebay for less than $100. Of course, it is also possible that the network is being trashed due to a bad ground, bad network connector, or even a failed suppressor in the alternator. That last one should only cause the problem if the engien is running.

 

You could try this.
When the window is functional, lower all the way.
Now press and hold window down for a few seconds.
You might hear a quiet thunk.
Now raise the window all the way up.
Now press and hold window up for a few seconds.
Again, you might hear a quiet thunk.
Repeat this for the sunroof.

For the S Type, this is a form of reseting the window limits and auto-up and auto-down functionality. Same for sunroof.

What's it gonna hurt to try?

 

Ok i will reboot and try tomorrow. Its gotta be something in the door i never use the roof but i will do both and report back thank you guys!

 

Hi
Here are 2 Electrical JPEG files:

Driver Front Door Module Pinout Diagram:
https://www.dropbox.com/s/y32419gi4b...Out%20Info.jpg

1998 XJ Driver Front Door Module Functions Wiring Diagram (Window Lifts & Sliding Roof):
https://www.dropbox.com/s/6i14w8s3hs...ing%20Info.jpg

Click on the weblink and it will open to webpage, then click on image that on the webpage, then increase zoom level to 125%.

Jim Lombardi

 

Im getting so mad im about to sell it!!!!!!!!! Hard reboot.... Worked for 10 mins shut it off and restarted and NO driver power window and sunroof opening and closing on its own! I have had about enough!

 

You have capably worked through your other horrors. You just need to fix this one via logical troubleshooting. Start with the SCP bus diagram. See if you can find an SCLM to borrow or on the cheap. Try and identify the minimum set of events that seem to cause the action, then post the exact sequence.
As in, "I start my car normally, let it idle for ten minutes, then shut it down and remove the key from the ignition, I get out of the car and ten minutes later, the roof opens to full open then closes, then the horn beeps" Or whatever. You have a wierd one, but just like everything elso, the problem has a simple, but just well hidden answer,

 

I can second that advice-electrical faults very often have an exasperatingly simple cause which can throw up all sorts of odd behaviour on the complex electronic systems on these cars.

The only way to locate the fault is to sit down with a strong cup of coffee & carefully go through the circuit diagrams to try & understand how the systems work & are interlinked.

The cause of the fault is always a logical one-it can just take time to find it. I spent over 20 years as an Avionics/Electronics repair technician & sometimes we'd get faults that could take several days to pin down-even when working an 8-hour day in the workshops.

I printed out the full 150 or so pages of circuit diagrams for my 2001 XJR & keep them in a binder for reference. I find out as much as I can about how the systems actually work too. There's no easy way with electrical faults-you have to keep plugging away until you find the root cause.

Anyway, just imagine how you'd feel if you got so frustrated with the faults that you sold the car at a loss-and then the new owner finds that the fault was very simple & cost little or nothing to cure!

Use that as your motivation to keep fault-finding

Looking at my circuit diagrams, the Sliding Roof Control Module only has 8 connections on it:

1 for the ground
1 for the positive supply rail
2 for the motor
2 for the roof switches
2 from the Body Procesor Module

If you can establish that the 12v supply is present at the Module, then that rules out a fault in the first 2 connections from the list above.

The second 2 connections are for the motor-which is obviously working, so those 2 connections can also be ruled out.

The third 2 connections are from the roof switches-these can be ruled out as they are unlikely to both fail at once at the same time. Also, once the ignition is off & the car is in 'sleep' mode they shouldn't be 'active' anyway.

So this leave the remaining 2 connections, which go to the Body Procesor Module-this is linked via the SCP network to the Window Lift Control Module & also to the Security & Locking Control Module

One way to check these modules is to locate them & then 'tap' them with a screwdriver handle-very often intermittent electrical faults in modules can be traced by tapping them to vibrate any faulty solder joints inside.

The cheapest way to do this is to wait until the fault appears, then tap the modules to see if the fault goes away.

Alternatively you can try & borrow the suspect modules of see if you can buy them cheap off ebay. I'm thinking that because you've got 2 faults at the same time, the fault may be in a module which is linked to the operation of both the window & roof:

Security & Locking Control Module (SCLM)
Body Processor Module (BPM)

Then we have the individual modules:

Driver Door Control Module
Sliding Roof Control Module

 

The thing is i dont use the roof at all so its not that. Its been in the 20's here. It HAS to be me using the key to lock and unlock, somehow, i can rattle the door, rattle the door module, move around the wires, open and close the windows 50 times in a row. Then roll up windows, shut off car, lock door and later go unlock, let system check complete, start up and there will be no power driver window. And if i open the roof it closes all by itself. All the other windows and security system still work fine. Just those 2 things.

 

Im gonna try to hard reboot and NOT lock or unlock the doors and see what happens. This is scary for me because i have a high dollar stereo in the trunk. Of course i guess i could put it in valet mode and that would secure the trunk. Im at a loss. Does anyone have a key fob they would sell that i can program to me car?

 

The only other thing not working is the gas flap. It does not even move. Wonder if that could be an issue?

 

Well..... Its been a few days of not locking and everything is still working properly! What's this mean?

 

It means you are experiencing that special charm of Jaguar ownership. I'm betting the next time the roof opens will be in a freezing rainstorm!