These instructions apply to the Lexus UX Mk1 (A1) 2019-Present.
For other models, please choose your vehicle here.
Disconnecting the 12 V battery on your Lexus UX (2019–present) is a job most owners can do at home — you might be fitting a fresh battery, laying the car up for winter storage, or working near the airbags before some interior or electrical work. The one thing that trips people up is where the battery actually lives, because on both the UX 250h hybrid and the UX 300e electric it is not sitting under the bonnet where you would expect it. Done in the correct order, the UX relearns everything it needs within a short drive, so there is nothing to be nervous about as long as you follow the sequence below.
Where the 12 V Battery Is
On the UX, the 12 V battery is in the luggage area, under the boot floor. Lift the boot floor panel and you will find it tucked to one side, usually under a cover. The terminals under the bonnet are jump-start points only — they are wired back to this battery but are not the battery itself. This 12 V battery is the one that feels the memory presets, the clock and the low-voltage electronics; it is entirely separate from the high-voltage drive system. On the hybrid and the EV, never touch the orange high-voltage cabling or the traction battery — that side is not owner-serviceable and carries a lethal voltage. Everything in this guide concerns the 12 V battery alone, which is as safe to handle as the battery in any conventional car.
Identify the terminals before you touch anything: the negative (−) post carries the black lead and is the earth, while the positive (+) post carries the red lead and is usually hidden under a red or orange plastic flap. Getting these the right way round matters, so take a moment to confirm which is which.
Before You Begin
- Make sure the car is fully off — not in READY mode — and take the smart key several metres away so the car cannot wake up.
- Switch off the lights, climate control, radio and any accessories, and close the doors.
- Note down your radio presets, any security code and personal settings so you can restore them quickly afterwards.
- Wait a couple of minutes after switching off for the modules to power down before you loosen anything.
- Have the correct spanner ready, and wear gloves and eye protection when working around a battery.
Disconnecting the Battery
- Confirm everything is switched off and the car is out of READY mode.
- Lift the boot floor to reach the battery and, if fitted, unclip any protective cover.
- Loosen the clamp on the negative (−) terminal first, lift the lead clear and tuck it aside so it cannot spring back onto the post.
- Now loosen and remove the positive (+) lead.
- If you are working near the airbags or seat-belt pretensioners, wait about 90 seconds after disconnecting before you begin, so those circuits fully discharge.
Reconnecting
- Refit the positive (+) terminal first and tighten its clamp.
- Reconnect the negative (−) terminal last and tighten it.
- Check both clamps are secure — a loose earth causes odd electrical faults — and refit the cover and boot floor.
What You’ll Need to Reset Afterwards
Because the UX loses its short-term memory while the battery is off, a few things come back either by hand or as the car relearns them on the move:
- Clock, radio presets and personal settings — re-enter these from the touchscreen.
- Steering-angle sensor — drive a short distance in a straight line and turn the wheel fully each way so the stability system re-references centre.
- Parking-assist and camera calibration settles as you drive and manoeuvre.
- Power windows — if the one-touch up/down stops working, cycle each window fully to re-initialise it.
- A few warning lights may glow briefly and then self-clear once the relearns finish over the first short drive.
If a Warning Light Stays On or the Car Feels Off
- Recheck that both terminals are clean and tightly clamped — this is the most common cause of trouble after a reconnection.
- Give the car a short, gentle drive with a few full steering sweeps so the steering-angle and assist systems complete their relearn.
- If the windows or driver-assist features still misbehave, repeat the relevant re-initialisation.
- Rule out a genuinely flat or worn-out battery — if it would not hold charge, the fault sits with the battery, not the reconnection.
- Any light that refuses to clear has stored a code — look it up on autodtcs.com.
Frequently Asked Questions
Where is the 12 V battery on a Lexus UX?
It is in the luggage area under the boot floor, usually under a cover. The terminals under the bonnet are only jump-start points, not the battery itself.
Which terminal do I disconnect first?
Always the negative (−) terminal first when disconnecting, and reconnect it last. On reconnection, the positive (+) goes on first and the negative last.
Is it safe to disconnect the 12 V battery on the hybrid or EV?
Yes. The 12 V battery is completely separate from the high-voltage traction system, so it is safe to handle. Just never touch the orange high-voltage cabling or the traction battery.
What needs resetting after reconnecting?
The clock, radio presets and settings are re-entered by hand, while the steering-angle sensor, parking-assist and windows re-initialise, mostly as you drive and use them.
Does a new battery need coding on the UX?
A like-for-like replacement of the same type and capacity does not need special coding for most owners. Fit the correct battery type and the charging logic will settle on its own.
Can I jump-start the UX instead of disconnecting?
If the 12 V is simply flat you can jump-start from the under-bonnet terminals to recover it, which avoids losing your settings. Disconnecting is for renewal, storage or working near the airbags.
If a warning light stays on after reconnecting the battery, look up the stored code on autodtcs.com.
Independent guide — not affiliated with Lexus. Always follow your official service manual and safety precautions. Read our full disclaimer.