Start the Car With a Dead Key Fob Battery

The Lexus NX (Z2, 2022–present) is built around Smart Access keyless entry and push-button start, with NX 350, NX 350h and NX 450h+ plug-in hybrid variants all sharing the same key system. When the smart key’s coin cell dies, the door sensors and remote buttons stop working — but the car can still read the key’s passive chip if you hold the fob right against the start button. This guide shows an NX owner how to start the engine and unlock the doors with a dead fob, then how to fit a fresh coin cell.

Start the NX with a dead fob battery

The second-generation NX has a back-up antenna in the ENGINE START STOP switch that can wake the key’s transponder at close range:

1. Get in, close the door, and press the brake pedal firmly.
2. Hold the smart key with the Lexus “L” emblem facing the START STOP button.
3. Touch the emblem side of the fob to the button. You will hear a beep as the car recognises the chip and the button indicator changes.
4. With your foot still on the brake, press the START STOP button. The NX 350 fires the engine; the NX 350h and 450h+ hybrids show READY.

If it does not take immediately, hold the fob flat to the button and try once more.

Unlock the doors with the mechanical key

A dead fob will not trigger the touch-to-unlock door handles, so use the hidden metal key:

1. Slide the release catch on the back of the smart key and pull out the emergency key blade.
2. At the driver’s door, remove the small cover at the rear of the door handle with the blade tip to expose the keyhole.
3. Insert the blade, turn to unlock, and open the door. If the alarm sounds, it stops once you touch the fob to the start button and switch the car to ON.
4. Slide the metal blade back into the fob so it is not misplaced.

Why touching the fob to the button works

Inside every Smart Access fob is a passive immobiliser chip that draws no battery power — it runs on an induced field. The START STOP button contains a small antenna that, when the fob emblem is held against it, energises that chip just long enough to verify the right key is present. This is the manufacturer’s designed-in backup, so it works even with a completely flat coin cell.

Replace the smart key battery

The Z2 NX smart key uses a CR2032 lithium coin cell (verify against the marking on the cell you take out). To change it:

1. Slide out the metal emergency key.
2. Insert a coin or small flat screwdriver into the slot the key left and twist gently to separate the case halves.
3. Remove the old CR2032 — the “+” face points up toward the back of the case.
4. Fit the new cell, snap the case shut, and reinsert the metal key.
5. Confirm the lock buttons and proximity sensing work before you rely on the fob again.

Expect roughly one to two years per cell. The NX dash shows a “key battery low” message when it is time.

Frequently Asked Questions

Does the NX 450h+ plug-in start the same way? Yes. Touch the fob to the button, press the brake, press START; the hybrid system displays READY rather than cranking.

Where is the hidden keyhole? Under a snap-off cap at the rear of the driver’s door handle — pry it off with the metal blade.

Will manual unlocking set off the alarm? It may. Touching the fob to the START STOP button and switching to ON clears it.

Which coin cell does the 2022-on NX key use? A CR2032 in most cases. Always check the print on the old battery before buying.

Can I keep driving after a touch-start? Yes, the engine stays running normally. But the dead fob still cannot operate the doors remotely, so replace the cell promptly.

If the dead-fob event left a warning light on the dash, you can decode any trouble code at autodtcs.com.