A key fob that suddenly stops working is most likely suffering from a dead battery — this is the cause in ~80% of cases. Replace the CR2032 (or other coin cell) first. If that doesn't fix it, the fob has probably lost its sync with the car and needs to be reprogrammed. Less commonly, the fob has signal interference, water damage, or a physically broken button. Work through the checklist below in order.
Troubleshooting Checklist — Work Through in Order
Replace the battery
Even if the battery is "only a year old," try a fresh one. Coin cells can fail early, especially cheap generics. Most fobs use a CR2032 — the type is printed on the existing battery. See the full battery replacement guide. Cost: ~$1.
Check battery orientation
If you recently changed the battery yourself, make sure the positive (+) side is facing the correct direction. A backwards battery won't damage the fob but it won't work. Open the fob again and verify — the positive side usually faces up (toward the circuit board).
Re-sync the fob to the car
Swapping a battery — or a flat car battery — frequently causes the fob to lose pairing. The re-sync procedure varies by brand:
- Most US vehicles: Sit in car, insert key, turn to On (not Start) 8 times within 10 seconds, press any fob button within 5 seconds. Car locks/unlocks to confirm.
- Toyota/Lexus: Turn ignition On/Off 4 times within 5 seconds, then press Lock on fob within 3 seconds.
- Ford/Lincoln: Turn key On/Off 8 times within 10 seconds (last position = On), press any fob button within 8 seconds.
- GM (Chevrolet/GMC/Buick/Cadillac): Hold Lock + Unlock on fob for 15 seconds.
See our full programming guide for a complete brand-by-brand table.
Test for signal interference
Move to a different location — at least 20 metres from large metal structures, electrical substations, Wi-Fi routers, or other vehicles. Parking garages and multi-storey car parks are notorious for blocking fob signals. If the fob works in a different location, interference was the problem.
Inspect for physical damage
Open the fob and look for: cracked circuit board, corroded battery contacts (greenish residue), snapped button membranes, or loose internal components. Clean corroded contacts with a cotton swab dipped in isopropyl alcohol. Broken button membranes can be replaced cheaply — search Amazon for your fob model + "button pad replacement".
Water damage treatment
If the fob was exposed to water: remove the battery immediately, rinse the circuit board with 90%+ isopropyl alcohol to displace water, and leave it in a warm dry place for 24–48 hours. Then try a new battery. Do not use a hairdryer — heat warps plastic. Many fobs recover if treated within an hour of getting wet.
Try a locksmith before the dealer
If none of the above works, a qualified automotive locksmith can diagnose and reprogram your fob with professional OBD tools — usually for $50–$100, significantly less than a dealer visit. If the fob itself is faulty, they can supply and program a replacement on the spot.
Key Fob Symptom Guide
| Symptom | Most Likely Cause | Fix |
|---|---|---|
| No response at all | Dead battery | Replace battery |
| Works close up, not from distance | Weak battery | Replace battery |
| Stopped working after battery swap | Lost sync | Re-programme fob |
| Stopped working after flat car battery | Lost sync | Re-programme fob |
| Works sometimes, not others | Interference or failing battery | Replace battery; test different locations |
| One button works, others don't | Worn button membrane | Replace button pad or fob |
| Dropped in water recently | Corrosion / short circuit | Isopropyl alcohol clean, dry 48hrs |
| Cracked fob casing | Physical damage | Replacement fob + programming |