Disconnect and Reconnect the Battery

Disconnecting the 12 V battery on your Lexus CT 200h (2011–2022) — for a new battery, winter storage, or work near the airbags — catches owners out, because on this hybrid the 12 V isn’t under the bonnet, it’s in the boot.

The CT 200h is a full hybrid, so it carries two separate electrical systems. The big traction battery under the rear seat runs the electric motor at high voltage and is sealed for life — you never go near it. The small 12 V battery in the boot is an ordinary lead-acid unit that wakes the car up, powers the computers before the hybrid system boots, and keeps the memory alive. That is the one you disconnect for a battery renewal, before bodywork or electrical repairs, ahead of long storage, or to reset a car that has been sitting with electrical gremlins. Done in the right order, the CT relearns everything it needs within a short drive, so there is nothing to fear here.

Where the 12 V Battery Is

The 12 V battery is in the luggage compartment (boot), usually on the right side under a trim panel. Lift the boot floor and any side liner to reach it — you may need to peel back carpet or release a couple of clips. The two studs under the bonnet, near the fusebox, are jump-start posts only; the actual battery is not up front on this car. Once you have the battery exposed, identify the two terminals: the negative (−) is the black clamp, usually with a bare cable to the bodywork, and the positive (+) is the red clamp under a plastic cover. As with any hybrid, never touch the orange high-voltage cabling or the traction battery — the 12 V work you are doing is completely separate from and independent of the HV system.

Getting Ready

• Make sure the car is fully off and not in READY mode — the dash should be dark, with no “READY” light showing.
• Take the smart key well away from the car so it cannot wake the electronics.
• Switch off the lights, climate control and anything else drawing power, and close the doors you are not using.
• Note down your radio or navigation security code if the car uses one, and jot down your seat and mirror positions.
• Have the right spanner ready (usually a 10 mm), plus gloves and eye protection, and give the electronics a couple of minutes to power down after switching off.

Disconnecting Safely

1. Confirm everything is switched off and all electrical consumers are dead.
2. Remove the boot trim to reach the battery, then slacken and lift off the negative (−) terminal first. Tuck the loose clamp aside so it cannot spring back onto the post.
3. Now slacken and remove the positive (+) terminal.
4. If you are working near airbags or seat-belt pretensioners, wait 90 seconds after disconnecting before starting that work, so the safety-system capacitors fully discharge.

Reconnecting and Re-initialising

1. Fit and tighten the positive (+) terminal first.
2. Fit and tighten the negative (−) terminal last. Make sure both clamps are snug — a loose clamp is the most common cause of odd behaviour afterwards.
3. Refit the trim, get in with the key, and press the power button to READY.

What You’ll Need to Reset Afterwards

The CT loses only short-term memory, and most of it comes back on its own:

• Clock, radio presets and settings — re-enter these, and the security code if prompted.
• Power windows — if one-touch and anti-pinch stop working, pull each switch up and hold at the top for a moment to re-initialise.
• Steering angle and stability systems relearn as you drive straight and turn fully each way at low speed.
• Seat and mirror positions if your car has memory settings.
• Some warning lights self-clear once these relearns complete over a short drive.

If a Warning Light Stays On or the Car Feels Off

• Re-check both clamps are tight and clean — this fixes the majority of after-disconnect faults.
• Take a short, gentle drive with a few straight stretches and full-lock turns to let the systems relearn.
• Repeat the window one-touch relearn if the express up/down still isn’t working.
• If the light persists, the battery may genuinely be flat or worn — a like-for-like small aux battery of the correct type is worth ruling in.
• Read any stored code to see what is really being flagged.

Frequently Asked Questions

Where is the 12 V battery on a Lexus CT 200h?

In the boot (luggage compartment), usually on the right side under a trim panel. Lift the boot floor and side liner to reach it. The posts under the bonnet are only for jump-starting, not the battery itself.

Is it safe to disconnect the 12 V on a hybrid?

Yes. The 12 V system is entirely separate from the high-voltage hybrid system, and disconnecting it is a normal owner job. Just never touch the orange HV cabling or the traction battery under the rear seat.

Which terminal do I disconnect first?

Negative (−) off first, then positive. On reconnection, positive (+) goes on first and negative last. Keeping to that order avoids accidental short-circuits against the bodywork.

Does a new 12 V battery need coding on the CT?

A like-for-like replacement of the correct type does not need dealer coding on this car. Fit the same size and specification, connect it in the right order, and the CT is happy.

Will disconnecting the battery clear fault codes or reset the service light?

It can clear some temporary stored codes, but it is not a proper service. A code that comes straight back points to a live fault, and the service reminder is a separate reset, not something a battery pull reliably clears.

Can I just jump-start it instead?

If you only need to get going after a flat, yes — use the under-bonnet jump posts. But for a battery renewal or work near the airbags you still need to disconnect the boot battery properly.

If a warning light stays on after reconnecting, look up the stored code on autodtcs.com.