P38 front window malfunction

Hi guys,
I spent a few hours working on the car yesterday, mainly for an oil-change. I just bought the car, so I wouldn't risk driving it on "someone else's" oil. I drained a measly 2.5 - 3 liters of sludge from the sump, so this wasn't a day to soon. I could actually hear the difference afterwards.

I then decided to try and cure the right front window, which doesn't move in either direction. When I push for window up, there's a beep and "window not set" is in the display. First, I checked every fuse in the car. All were ok, but I found an open space in the fuse box under the passenger seat, so I stuck a fuse in there for good measure (more of which later! ). No luck.
Next, I dismantled the central console switch panel, which was a fairly unserviceable unit. I found nothing wrong with it.

I then pulled the door panel off to check the actuator and connections. Nothing obviously wrong here, but I drilled out the rivets and removed the actuator for testing. Looking at the connector, there are 2 fat cables and 4 thinner ones. I figured that the fat ones must be power and the others signal cables, telling the computer the position of the window. So I hooked the corresponding power pins to a 12V supply and the mechanism churned merrily away (both directions). So the motor is OK.

I worked out that most - if not all - the cables from the connector originate in the "door out-station", so I pulled this apart. Now I understand why these cars suffer from electrical gremlins - it's like NASA in there!
I was surprised that this mega-computer wasn't waterproofed in any way, but I couldn't find any traces of moisture inside. What I did find was three relays. One of them clicks away when I operate the mirror, so I suppose the other two are for the window, or maybe one each for the window and door latch. Anyway, nothing clicks when I operate the window switch, so there's no power to the motor. And now I'm stuck.

I can think of a number of culprits:
- Defective out-station computer
- Defective relay in the out-station
- Another computer, controlling the out-station, is malfunctioning.
- The control-part of the motor is busted, so that the out-station isn't getting the right feedback.

Any ideas? Will a visit to the dealer and his diagnostic apparatus pin-point where the fault lies, or is my guess as good as theirs?

I checked the dead electric door latch as well and it was very wet to the touch, so I guess it's been killed by water. Can it be opened so that I can replace or repair the guts? The switching function is OK, as it actuates the other doors when I operate the lever.

After putting it all back together I got in to drive home, but WTF? The car wouldn't budge, there was a message in the display reading "transfer neutral", and it sounded like a bucket of nails when I stuck it in park. After quite a bit of hair-pulling, foul language and rage, I got on the computer and started investigating. I finally worked out that the missing fuse I'd replaced is supposed to be missing. It's to be put in for towing and disengages the transfer case. Pulled the fuse and everything was back to normal.

What a night!

Regards,
Henrik

Favorite is a failure of the window switch in the centre console. Go for the easy things first!

Datatek said:

Favorite is a failure of the window switch in the centre console. Go for the easy things first!

Click to expand...

I did check the switch. It's on a circuit board, so that would mean replacing the wole board, with all four window controls plus the mirror control. I do believe the switch is working, as the computer obviously registers that I push it (there's a beep and the "window not set"-message appears on the dash).

Could an incident with reversed jumper cables (sparks flew!) have fried something?

Does anybody know how much detail I could expect on the location of the failure, if I hooked the car up to a fault code reader at the dealer's?

Thanks!
Henrik

Henrik97 said:

I did check the switch. It's on a circuit board, so that would mean replacing the wole board, with all four window controls plus the mirror control. I do believe the switch is working, as the computer obviously registers that I push it (there's a beep and the "window not set"-message appears on the dash).

Could an incident with reversed jumper cables (sparks flew!) have fried something?

Does anybody know how much detail I could expect on the location of the failure, if I hooked the car up to a fault code reader at the dealer's?

Thanks!
Henrik

Click to expand...

Yes you certainly could have fried some of the electronics. They are very sensitive to reverse voltage spikes

Well, lads,
I've now witnessed the magical self-healing properties of the RR electrical system first hand. Pushed the switch again today while stuck in traffic and hey, presto! Works like a charm!
Don't know why, but it probably just takes a huge number of stop-starts for this system to reset after a flat battery.

I did pull the door apart and spend hours in there, but luckily I didn't get round to buying any parts before it cured itself!

Perplexing...

Henrik

Dodgy switch or bad connection, how long do you give it before the fault reappears?

Datatek said:

Dodgy switch or bad connection, how long do you give it before the fault reappears?

Click to expand...

As long as it takes, quite simply. I'm not about to start replacing parts and pulling things apart as long as it works. If we were talking about brakes or gearbox, it'd be a different matter, but a passenger window lift isn't exactly a critical component. I'm just glad it works again.