Jaguar S-Type Battery Drain, Battery Flat Overnight
With a good battery, the S-Type usually goes flat because it never goes to sleep — it thinks the key is in or the ignition is on. I'd look first at the ignition switch and lock cylinder, and the flap in the key slot: cheap mechanical fixes that come before any fuse hunt. A healthy car settles to about 30–40 mA, but only after about 45 minutes.
How bad is it · Safe to drive
Safe to drive — the risk is being stranded
A battery run completely flat a few times loses capacity for good, and on this car a weak battery throws a shower of unrelated faults. If the headlamps come on by themselves with the key in your pocket, fix it before you next leave the car overnight.
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 ignition switch or lock cylinder doesn't return fully to off
The key turns the lock cylinder, whose shaft turns the switch behind it. A worn switch, or a shaft tip worn loose in it, leaves the switch short of off — the accessory feed stays live.
Key out, yet the radio or clock stays on, the chime sounds, the remote won't lock; headlamps may come on by themselves. Turning and pulling the key in one movement makes it worse.
Pull the radio's switched-feed fuse with the key out: if the radio dies, the switch is still passing current. A mushy detent at 0 is a clue. Before buying a switch, check how tightly the cylinder shaft fits into it.
A new ignition switch — a known issue on early cars. If the shaft tip is worn, a new switch won't help: build the tip up with steel epoxy and file it to fit, and the detents come back crisp.
The key-slot flap sticks — the car thinks the key is in
A switch in the lock cylinder, pressed by a small spring flap, reports whether a key is present. Stuck open, it keeps the car awake.
Door chime with the door open and no key in. A new battery goes flat like the old one.
A few drops of silicone or lock lubricant on the flap, then work the key in and out until it closes every time.
Lubricate the flap and work it until it closes; the car then holds its charge for days.
Early cars: bulletin S414-02, the junction-box feed
On early production cars high resistance in the feed to the main junction box stops the system shutting down. The cure is a bypass lead from the body module on the left kick panel to the junction box on the right; a dealer can check the VIN range.
With the car off, a relay in the boot fuse panel is warm. The headlamps flash every half hour or so while parked.
Feel the relays; ask a dealer to check S414-02 against the VIN. No tell — look elsewhere first.
Fit the bypass lead. It can transform the drain — for example from about 3.5 V lost in 24 hours to 0.05 V — but not always: sometimes it changes nothing, or cuts 5 A to 1.5 A and the battery still goes flat.
Left awake: key at position I, or a cover over the exit lamps
The key left at position I keeps the accessory circuits live. The exterior lamps stay on for about a minute after you leave; cover the car too soon and they may stay on all night.
Totally dead in the morning, sometimes with the radio or other modules behaving oddly afterwards.
Key out, not just turned back. Let the exit lamps go out before covering the car. Even at Off, a key left sitting in the barrel keeps a separate key-in contact live to the immobiliser, enough to flatten it over a couple of days.
After a really deep flat, charge the battery with the earth lead off until it fully recovers; the modules then come back to normal.
A tired battery left standing for weeks
Even asleep the car draws a little for the alarm and the memories. Over weeks unused, an ageing battery falls below what the security system needs to let the engine start, and every deep flat shortens its life further.
Flat only after a long lay-up, not after a weekend. The security light flashes at key position II and the engine won't start, while the boot lamps still work.
Find out the battery's age; past about four years, replace it. Then charge fully and measure the locked draw — if that's normal, the battery itself is the fault. After many complete flats, try a known-good battery before hunting for a drain.
A jump start gets it going; a maintenance charger keeps a rarely used car ready.
A battery loose in its mounting
A battery that moves strains and loosens its connections, and a poor connection looks like a flat battery.
Flat only now and then, better after a jump that jolts the cables.
Make sure the clamp and both terminals are tight.
Tighten the clamp and terminals.
The dealer transit wiring in the boot
New cars carry a transit isolation relay that the first dealer removes, tucking its wires away. The loose connector left in the boot can corrode or sit in water and cause all sorts of electrical trouble.
Water in the boot well; a small white plug with loose wires near the battery negative or the right rear lamp.
Find it, dry it, tape it off and tie it up clear of water.
Worth doing: tape off and tie up the unused connector, and keep the boot well dry.
The alarm backup sounder and its internal battery
The backup sounder carries a small rechargeable battery. When that fails, the car keeps trying to charge it.
A drain with nothing obvious left on and the alarm otherwise normal.
The silver sounder sits forward of the engine-bay fuse box — lift the box, or go through the right front wheel-arch liner. Unplug it and see whether the drain stops.
Worth trying: leave the sounder unplugged, especially if age or water has got to it.
Measure the draw properly, then find the circuit
The car shuts down in stages. Reconnecting the battery or opening a door or the boot wakes the modules again, and it takes about 45 minutes to fall to 30–40 mA.
More than about 50 mA after the car has been left undisturbed for well over half an hour.
Ammeter in the negative lead; open doors and boot and close their latches with a screwdriver. Lock it and wait — for example, from about half an amp to 50–55 mA over a day. Then pull fuses one at a time; each disturbance restarts the wait. Quicker, and without waking anything: read the millivolt drop across the metal link of every fuse in all three boxes. A fuse with no drop feeds nothing; the one that shows a drop names the circuit. A clamp meter at a sensible price can't read low enough.
This finds the less common ones: the alarm bonnet switch, a wiper motor that keeps trying to park after switch-off, or on a 2.7 diesel a failing secondary coolant pump relay. Also a telephone and navigation feed in the boot on a car with the phone hardware fitted but never activated — about a quarter of an amp — and a fault traced through the front electronic module by unplugging its connectors one at a time, with another 45-minute wait after each.
A lamp that never goes out: glovebox, boot, puddle or courtesy
Each of these lamps has its own switch or timer. When a switch sticks, the lamp stays lit behind a closed lid and keeps the circuit awake all night.
A steady draw of a few hundred milliamps that never falls away, often with the radio or lamps the only suspects.
Check that the automatic lamps are set off when parked, then look into the glovebox, boot and footwells in the dark with the car locked. Press each lamp switch by hand and watch the lamp go out.
Worth trying: free or replace the sticking lamp switch.
A relay stuck on, such as the A/C clutch relay
A relay whose contacts weld or whose coil stays fed keeps its circuit running after shutdown. It may do it only some nights, which makes it slow to catch.
A drain that comes and goes; a relay that's warm when the car should have been asleep for an hour.
After the car has shut down, feel each relay in the fuse boxes for warmth and read the millivolt drop across the fuses. Swap a suspect relay with an identical one and measure again.
Worth trying: replace the warm relay. The A/C clutch relay in the front fuse box is a known culprit; a CD changer that stays awake is another.
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.
Key out: is anything still alive?
Radio, clock, chime with the door open, headlamps. Any of these means the car thinks the key is in or the ignition is on. One exception: a radio switched on by hand with the key out is allowed to play, and turns itself off after about an hour.
freeFree the key-slot flap
A drop of lubricant, then key in and out until the flap closes.
freeEarly car? Feel the relays in the boot panel
Warm with the car off, and headlamps flashing now and then: ask the dealer about bulletin S414-02.
freeCheck the battery clamp and the boot transit wires
Dry the boot well, tape off and tie up the loose plug.
freeMeasure the draw after 45 minutes
Latches closed with a screwdriver, nothing disturbed. 30–40 mA is healthy.
a multimeterSuspect switch? Check the shaft first
A worn lock-cylinder shaft makes a new switch misbehave the same way.
a switchHave the radio code before disconnecting
And expect the windows and parking brake to need re-initialising.
freeThe fuses named above — where they sit
The highlighted position is the one the procedure talks about. Pulling a fuse is a stop-gap, never a repair: check what the circuit feeds before you pull it.
Circuit descriptions from the Jaguar handbook, 2007 edition, p. 9, 10. Drawing by jagaux.com from the factory electrical guide. Fuse layouts change between model years — read the legend on the lid of your own box before pulling anything.
Circuit descriptions from the Jaguar handbook, 2007 edition, p. 7, 8. Drawing by jagaux.com from the factory electrical guide. Fuse layouts change between model years — read the legend on the lid of your own box before pulling anything.
What it usually isn't
Don't spend money here first:
If none of this finds it:
On jagaux.com
- Jaguar S-Type Won't Start, No CrankIf the battery is fine and the starter still does nothing.
- Jaguar S-Type Central Locking ProblemsIf the doors lock and then unlock themselves, or one door won't lock or open.
- S-Type fuse boxes, 2000Early layout; other years from the same page.
- Jaguar radio code generatorFree. For when the radio asks for its code after the battery has been off.
- Jaguar S-Type Headlights Not WorkingIf the sidelights stay on after you lock up and flatten the battery, the light stalk is a suspect.
- Jaguar S-Type Water Leak, Water in BootDamp-weather drains often start with water in the spare wheel well.
- Jaguar S-Type Parking Brake FaultIf the electric parking brake locks on whenever the battery runs down.
- Jaguar S-Type Wipers Not Working, Wiper LinkageIf the battery goes flat since the wipers stopped short of park.
- 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.