Jaguar I-Pace 12V Battery Drain, Car Won't Wake
The I-Pace has two kinds of battery: the traction pack that drives it, and the 12 V battery (two of them on pre-MY21 cars) that runs the electronics and wakes the car up. A pack that loses charge while parked, a dead car in the morning or a sudden Reduced Brake Pedal Feel warning is almost always the 12 V side. I'd start by looking at the hazard switch through the window 10 to 30 minutes after locking: if it is still lit, the car hasn't gone to sleep.
How bad is it · Garage, carefully
Don't ignore 12 V warnings — get it seen before relying on the car
When the 12 V supply fails the car can lose the brake booster, the park lock and drive, sometimes on the move. A Reduced Brake Pedal Feel or charging-system warning is the moment to act, not something to drive around.
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 car never goes to sleep: module software
After locking, the modules should shut down in turn. If one misses the shutdown message the network stays awake, the DC-DC converter keeps topping up the 12 V from the pack, and the pack loses several percent a night. Corrupted gateway module (GWM) software is a known cause.
The hazard switch stays lit long after locking. A 12 V monitor shows charging voltage, around 14.4 V, all night instead of a resting voltage. The phone may reconnect over Bluetooth hours after the car was locked.
The hazard switch should go dim about 10 minutes after locking, or 30 minutes if left unlocked. Ask the dealer for the software levels of the gateway, body control and telematics modules, and for bulletins SSM74458 (parked drain test) and SSM74531 (12 V flat after HV charging, the network kept awake and the GWM freezing).
Reprogramming the gateway module under service action N392, done with the Pathfinder tool rather than TOPIx Cloud: the 12 V settled to its resting voltage about an hour after locking. Updates to the GWM, BCM and telematics module cure the same fault.
A tired 12 V battery the car keeps charging
A 12 V battery with failing cells won't hold its charge, so the car keeps waking the DC-DC converter to refill it and the pack drains. When the 12 V sags, monitoring circuits are starved and report false faults such as Traction Battery Fault Detected.
A small overnight loss, for example 2–3%, for a few days before the car is found dead. Traction Battery Fault Detected, an alarm going off, or an app warning of a low 12 V, for example 12.1 V.
A Bluetooth monitor on the battery for a few days: a healthy one shows voltage falling gently at rest, a failing one dips below 13.0 V and spikes above 15.0 V. Have it load-tested; a no-load voltage reading proves little.
Replace the 12 V battery and have the software brought up to date at the same visit. Once a 12 V battery has been deeply flattened, replacing it is the safer choice even if it recharges.
Weak or loose auxiliary battery: brake and gearbox warnings
On pre-MY21 cars the small auxiliary battery feeds the brake booster, the parking lock and the front inverter. A weak cell or a loose cable there gives brake and gearbox warnings while everything else looks normal.
Reduced Brake Pedal Feel, drive with caution, a gearbox fault, the car refusing to leave Park or shutting down seconds after switching on. A code such as U3007-16 for the brake booster supply. The car may simply not move with a battery fault on the screen.
Measure both batteries: a starter battery at 14.47 V next to an auxiliary at 5.46 V leaves no doubt. Check the auxiliary terminals are tight before buying anything.
Tighten a loose auxiliary cable, or replace the auxiliary AGM battery (Exide EK151 or the JLR part). A recharge clears the message for a while, but it comes back.
The charging hardware: DC-DC converter or power distribution box
There is no alternator: the 12 V side is charged from the pack by the DC-DC converter, through the power supply distribution box. If either fails, new batteries go flat again within a week or two.
New 12 V batteries help only briefly. A monitor shows the small battery never charging while the big one is charged constantly. The hazard switch stays lit despite updates.
Log both batteries with Bluetooth monitors and show the logs to the dealer: they separate a battery fault from a charging fault. Software first, since an update to the BECM and BCCM got a non-charging auxiliary battery charging again.
Replacing the power supply distribution box (JT4A 48077, about £537 on one car) made the hazard light go out at rest. Other cars needed the DC-DC converter and the wiring junction box.
It's the key fob, not the car
A car that ignores the fob and the door button looks dead. With a flat fob battery, the car and its batteries can be perfectly fine.
No response to the fob, while a red battery-like icon blinks on the dash seen through the window.
Try the second fob before anything else.
The second fob opened the car; fit new fob batteries to both.
Accessories on the always-live supply
The OBD socket has an always-live 5 A supply. A dongle left in it, or a dash cam wired for parking mode, can drain the 12 V overnight. A pre-conditioning timer also runs when the car is locked and unplugged.
Drain that began after fitting a dash cam or an OBD reader for a phone app; 10% gone in two days with nothing else wrong.
Unplug the dongle and the dash cam, look at the pre-conditioning schedule, then watch a few nights.
Worth trying first: removing the OBD reader stopped the overnight drain on one car.
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.
Second fob first
If the car won't respond, try the other fob and a fresh fob battery before assuming a flat 12 V.
freeGetting into a dead car
The emergency key blade sits behind the driver's door handle cap; the bonnet has an emergency release cable in the front footwell, as shown in the owner's manual. The 12 V sockets switch off about 15 minutes after shutdown, so a booster plugged in there does nothing.
freeJump the 12 V correctly
Booster positive to the battery, negative to a body earth rather than the small negative post, so the battery monitoring sensor sees the current. With both batteries flat, the starter battery needs help too.
freeWatch the hazard switch after locking
It should go dim about 10 minutes after locking. Still lit after half an hour means a module is keeping the car awake.
freeUnplug accessories
OBD dongle, dash cam, anything wired to a permanent feed. Check the pre-conditioning timer.
freeMonitor both 12 V batteries
A Bluetooth monitor on each for a few days shows whether a battery rests near 13.0 V or is charged around the clock, and whether the small one charges at all.
cheapLoad-test the batteries
The main battery is under the black cowl at the base of the windscreen. A tester under load tells more than a voltmeter.
cheapDealer: software and bulletins
Software levels of the GWM, BCM, telematics module, BCCM and BECM; bulletins SSM74458 and SSM74531; service action N392 if it applies.
dealer diagnosisThen the charging hardware
With the batteries good and software current, the DC-DC converter and the power supply distribution box are next.
dealer repairWhat it usually isn't
Don't spend money here first:
If none of this finds it:
On jagaux.com
- Jaguar I-Pace 12V Battery ReplacementWhich 12 V battery to buy and how to change it without upsetting the electronics.
- Jaguar I-Pace Key Fob Not WorkingIf the car only ignores the fob, start with the fob.
- Jaguar I-Pace Won't Charge, Charging Port ProblemsIf the 12 V is fine but the pack won't take a charge.
- 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.