These instructions apply to the SsangYong Rexton Mk3 (Y400) 2017-2022.
For other models, please choose your vehicle here.
The SsangYong Rexton (Y400, 2017–2022) runs a Smart Key with keyless entry and a push-button start, controlled by the Smart Key Module. A flat coin cell kills the long-range radio — the dash flags the key as undetected — but the car still reads the chip at close range, so a dead fob never leaves you stuck. Here is the fallback in full.
Start the Car With a Dead Smart Key
The transponder in the Rexton fob is passive; an antenna behind the START/STOP button powers and reads it from a centimetre away, so a flat coin cell does not stop a start:
- Get in first (mechanical-key steps below) and sit in the driver’s seat, door shut.
- Press the brake pedal fully and hold it.
- Hold the Smart Key flat against the START/STOP button, badge face to the button.
- With the brake down, press START. The Rexton cranks and starts.
No response? Reposition the fob square on the button or flip it to the other face; the read coil has only a couple of centimetres of reach.
Unlock With the Emergency Key
A dead fob will not unlock by radio, so use the blade inside it.
- Slide the catch on the Smart Key and draw the mechanical blade out.
- At the driver’s door, lever off the cover on the handle to reach the lock cylinder.
- Insert and turn to unlock. The alarm may sound until the car is started.
About the Immobiliser
The Rexton’s Smart Key Module handles the immobiliser. Holding the fob to the start button is SsangYong’s designed low-battery fallback — the close-range immobiliser link is separate from the radio used for hands-free entry, which is why it still authorises a start with a flat cell. If the car cranks but will not run, or the key warning stays after a fresh cell, the fault is the key or SKM, not the coin cell.
Replace the Coin Cell
The Rexton Smart Key uses a 3V lithium coin cell — commonly a CR2032, though some fobs of this era take a CR2025. The print on the old cell is the reliable guide.
- Pull the mechanical blade out to expose the case seam.
- Twist a coin or small flat screwdriver in the slot to part the halves.
- Note the old cell’s number, then fit the matching new one positive (+) side the same way, by the rim.
- Click the case shut and test lock/unlock at the car.
Frequently Asked Questions
How do I start the Rexton with a dead smart key? Hold the fob against the START/STOP button with the brake pressed, then push START.
Which battery does the Rexton smart key take? A 3V lithium coin cell, usually CR2032 or CR2025 — read the old one to be sure.
Where is the door keyhole? Behind a cover on the driver’s door handle; pop the cover off with the emergency blade.
Do I need to reprogram after a battery change? No. Swapping the coin cell does not erase the key; the remote works again once it is fitted.
Key still not detected with a new cell — why? Test the 12V battery first; a weak main battery can imitate a key fault. If it remains, the key or SKM needs checking.
If a warning light stayed on after you drove off, you can decode the exact fault on our sister site autodtcs.com to check whether it relates to the smart-key system.
Independent guide — not affiliated with SsangYong. Always follow your official service manual and safety precautions. Read our full disclaimer.