Jaguar XK8 Window Problems
On the XK8 a door window that drops further each time and won't come back up has usually lost its learned limits: a two-minute relearn fixes it, and a weak battery is why it keeps coming back. If the glass rises the moment you let go of the handle on one door, look at the door-open microswitch in that lock; if window, mirror and locks die together on one door, look for water in its plugs and switch pack. On the convertible, a rear quarter window that won't go up is either a broken regulator cable or the roof not telling the module it's closed.
How bad is it · Safe to drive
Safe to drive; just keep the glass shut
Nothing here affects how the car drives. A glass that won't come back up leaves the car open and lets rain in, and a door you can't shut without timing the handle is a nuisance, not a danger.
Which one applies to yours depends on your symptoms, your model year and what has already been done to it.
Likely causes, most common first
Read the check cost before the odds: a free check that rules a cause out beats a likely guess that costs money.
The window has lost its travel limits, usually through a weak battery
The frameless door glass drops a little when you lift a door handle and comes back up when the door shuts, so it clears the roof or hood seal. The door module learns where fully up and fully down are, and it loses that memory whenever the voltage falls below about 10 V: after a battery disconnect, or a tired battery dipping during cranking. The door modules and the ABS module are the first to forget, and a battery can still crank briskly while being too weak for them.
The glass drops further each time you touch the handle, doesn't come back up when the door closes, or stops auto-raising altogether. Often right after battery work or a spell standing, and it comes back within days if the battery is the cause. A glass frozen to its seal on a frosty morning can lose its limits the same way.
With the door shut and the ignition on, run the window fully down and keep holding the switch until it clicks, then fully up and hold until it clicks again. Do both doors; roof up or down makes no difference. If it doesn't hold, charge the battery fully and have it load-tested: for example, a battery that still cranked well tested at 339 CCA against a 600 rating.
The relearn itself cures the symptom in two minutes; do it from inside with the doors shut, and some cars need the switch held closer to 10 seconds before the click, or a second go on the passenger side. To stop it returning, charge or renew a tired battery, using a memory saver while it's out, check the terminals are tight after any disconnect, and keep a maintainer on a car that stands or does short runs. A battery cut-off switch means a relearn after every disconnect, so a maintainer is the better choice.
The door-open microswitch inside the door lock
A microswitch built into the door lock tells the car the door is open. The same switch holds the glass down and lights the courtesy lamp; when it fails, the module thinks the door is shut and raises the glass again.
One door only: the glass dips while you hold the handle and rises as soon as you let go, even with the door open, so you have to time the handle release to shut the door. That door also gives no courtesy light, no puddle light, and no DOOR OPEN on the message centre. The opposite failure, a switch stuck closed, leaves the glass down after the door shuts, keeps the door-open warning on and stops the fob locking the car.
Open each door in turn and watch the message centre and the interior lights. If one door gives no DOOR OPEN and no light, a relearn won't help. Before buying the lock, press the jamb switch by hand and look at the harness where it bends between the door and the pillar, because a broken wire there does the same.
Renew the door lock assembly with its microswitch; a good used one does the job. The microswitch alone is also sold, part C2N1908 — allow most of a day, as the outer handle has to come off first. The two door modules share a part number but are programmed for their side, so if you swap them to test, put them back or the driver's central locking stops.
Door glass out of alignment
The glass is set by alignment pins held with lock nuts. If the nuts loosen, the glass binds in its seals and can't make its little drop cleanly.
The glass drops only a fraction when you open the door and stutters, as if it can't decide which way to go, until you push the door past the roof seal. Often wind noise at the quarter window too. On the convertible, a rear quarter glass that stops a quarter of an inch short of the door glass.
Battery and relearn first. Then take the door trim off and check the lock nuts on the alignment pins.
Realign the glass to the workshop manual setting and tighten the nuts. Silicone on the roof window seals cuts the friction further. If a rear quarter glass doesn't meet the door glass, adjust the door glass first — it sets where the quarter glass has to stop; a new quarter regulator always needs setting up again.
The driver's door module — failed, or switched off by a door it thinks is ajar
The driver's door module runs both the window and the mirror. It switches them off if it thinks the door isn't fully shut, and it also stops if it loses power or ground through the harness that flexes at the hinge.
Driver's window and door mirror stop together, both the switch and the auto drop, and may come back on their own. With DOOR OPEN showing while the door is shut, and memory, mirror and courtesy lights also dead on that side, the module itself is a strong suspect once its three microswitches test good.
Make sure the door latches fully and the car doesn't think it's ajar. Then check the plugs and the harness running from the door to the A-pillar for water, corrosion and broken wires.
Cure the door-ajar fault or the broken feed first. If the module really must go, match the part number from the VCATS label in the boot by the spare wheel, last three digits included — the last two letters give the market, and a mismatched one needs programming. A used module with the right number does the job, for example about £27 against £80–150 new.
Water in the door: a corroded switch pack or door-to-body plug
Water finds its way into the switch packs and the plugs where the door harness meets the body. Corrosion there breaks the signal and earth paths the door module depends on, so window, locks and mirror drop out together and come back when it dries.
Driver window won't move or auto-drop, the doors don't lock on driving off and the alarm thinks the driver's door is open; it returns every few days. A used door module helps for a few weeks, then the fault is back. Or one door goes completely dead — window, mirror and lock — with good fuses.
Unplug the door harness where it enters the A-pillar and look for green corrosion; check the door module's earths with a test light rather than a voltmeter. Then open the switch packs, the mirror joystick pack included, and look at the circuit board.
Clean every plug and relay contact on that circuit and refit with contact grease; tighten loose sockets in the A-pillar plug. A corroded switch-pack board can be saved by bridging eaten tracks with fine tinned wire and recoating it.
A seized window motor
Corrosion and old grease inside the motor gearbox can lock it solid.
The glass doesn't move at all on the switch, and with the motor out the shaft won't turn even with a wrench.
Take the motor out and try to turn it by hand; bench test it on 12 V.
A seized motor isn't necessarily scrap: strip it, soak it in brake cleaner overnight and flush it with contact cleaner until the fluid runs clean, then dry and reassemble. A quick clean isn't enough.
A broken cable in the rear quarter window regulator
On the convertible each rear quarter window is driven by a motor and a cable regulator. When the cable snaps or tangles, the motor runs but the glass isn't held.
One quarter window won't rise; you hear the motor run on the switch, and the glass wobbles loose by hand.
Listen at that window while someone works the switch. A running motor with a loose glass is the regulator, not a relay or the module.
Renew the regulator. A cable repair kit exists but tends to fail again, so a sound used regulator assembly is the surer route. The workshop manual does the job with the roof taken off. As a stopgap the glass can be wedged shut, but then leave the roof up, since it can only lower with the quarter windows free to drop.
The roof system out of step, so the quarter windows aren't told to rise
The quarter windows rise only when the roof switches, the latch and the rams all report closed. If a cycle was interrupted, the system stays out of sequence and leaves the quarter windows down; the front glass can misbehave too.
A Hood latch failure message after the car has stood in the cold, the roof switch only lowers the quarter windows, and they won't come back up. Or the front windows play up and a relearn doesn't fix them.
Relatch the roof by hand with the Allen key at the header, then press close on the roof switch, or close it with the door key if the switch does nothing.
Worth trying before any parts: relatch by hand, then run a full cycle. With the front windows down, open the roof fully, then close it and let the quarter windows finish until the roof latches and the chime sounds.
A broken signal wire from the roof: ram connector or header wiring
A microswitch on a lift ram and wiring through the windscreen header tell the module the roof is fully up. A broken connector or wire there makes it think the roof is still open, so it never raises the quarter windows.
Both quarter windows stay down after the roof closes, typically soon after work on the rams, a quarter regulator or the windscreen.
Inspect the connectors on both rams and the wiring in the header above the screen. Check the quarter window relays in the boot: early cars have an up and a down relay per side, later cars a split relay per side. The roof module wiring diagram shows which pin needs a good ground. Swap the left and right relays to rule them out before chasing wiring.
Repair the broken connector or wire. The corroded connector under the rear seat is on the convertible top page.
Lost feed to the window switches
Both door switch packs take their supply through one small fuse in the passenger-side fuse box and several connectors on the way to the doors. Lose that feed and the switch can no longer command the glass, even though the motor and the module are fine.
The glass goes down but rises only part-way, then stops answering; pressing the switch just clunks the door lock. 12 V jumped onto the switch feed brings it back for a moment.
Unplug the switch pack and look for 12 V on its brown/white feed with the ignition on. If it's missing, work back from the fuse box through each connector on the wiring diagram; with the pack out, a meter across its pins tells a dead switch from a dead feed.
Worth trying before a module or a switch pack: renew the fuse and clean or remake the connector where the feed is lost.
The order to check them in
The point of the order is money: each step either rules a cause out or makes the next one worth doing. Green is free, amber costs a little, red is the one to arrive at last.
Know what's normal
The door glass dips a little when you lift a handle, rises when the door shuts, and dips during the roof cycle on the convertible. Only a drop that grows or a glass that won't come back is a fault.
freeRelearn the window
Door shut, ignition on: run the glass fully down and hold until it clicks, then fully up and hold until it clicks. Do both doors.
freeCharge and test the battery
If the relearn doesn't hold, charge the battery fully and have it load-tested; a good crank proves nothing here. Keep a maintainer on a car that stands.
a maintainer or a batteryCheck the door-open signal
Open each door and watch for DOOR OPEN on the message centre and the courtesy light. A door that shows neither has a failed microswitch in its lock or a broken wire at the hinge.
freeRun a full roof cycle
On the convertible, if the quarter windows stay down, relatch the roof by hand with the Allen key, then open and close it fully until the chime.
freeListen at a dead quarter window
Motor running and the glass loose means the regulator cable. Silence means the relays in the boot, the roof signal wiring or the connector under the rear seat.
freeCheck the door harness and latch
For a driver's window and mirror that die together, check the door latches fully, then unplug the harness where it enters the A-pillar and look for water and green corrosion; open the switch packs too. No 12 V on the switch feed sends you back to the fuse box.
freeRenew the faulty part
Door lock assembly, quarter window regulator or door glass alignment, whichever the checks above point to.
used lock about £80; regulator moreWhat it usually isn't
Don't spend money here first:
If none of this finds it:
On jagaux.com
- Jaguar XK8 Convertible Top ProblemsIf the roof itself won't move or latch, or the quarter windows drop while you drive.
- Jaguar XK8 Key Fob Not Working, Alarm or ImmobiliserIf the locks and alarm misbehave along with the windows.
- Jaguar XK8 Radio Code After Battery ChangeIf the radio wants its code after the battery was disconnected.
- XK8 fuse boxes, including the boot boxFind the quarter window relays and fuses in the boot box, drawn.
- Jaguar VIN decoderConfirm your exact model year, engine and factory options before ordering parts — free.
Ratings, fuse numbers and torque figures vary by model year and market. Read the legend on your own car before pulling anything, and use the figures in the manual for your car, not the ones in a video.
Check your VIN: exactly which car you have and which bulletins apply to it.