Quick answer
When a car key fob stops working, the causes in order of likelihood are: a dead coin battery, the fob losing its pairing after a car battery change or jump, a worn or broken internal blade or button contacts, signal interference or a damaged antenna, or a car-side fault in the receiver or start system. Try the emergency key blade, hold the fob against the start button, and replace the battery first. If it still fails, a mobile locksmith can diagnose and reprogram or replace the fob at your car. Fob replacement typically runs $175 to $450 in San Diego. See car key replacement.
In this guide
Two-minute checks before anything else
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1
Use the hidden key
Most fobs contain a mechanical blade. Slide the release, pull it out, and open the driver door with it. There's usually a keyhole under a cap on the handle.
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2
Hold the fob to the start button
Push-to-start cars have a backup reader in or near the button or a marked spot on the column. Hold the fob against it and press the brake and the button.
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3
Try the spare
If the spare works, the problem is the fob. If neither works, it's the car.
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4
Replace the battery
A coin cell from any drugstore. Note the orientation before you pull the old one.
Cause 1: the battery
The most common cause by far. Fob batteries last one to three years, and the first symptom is reduced range: you have to stand closer to the car. Replace it before it dies completely. Most fobs pop open with a coin in the seam; the battery type is printed on the old cell.
Cause 2: lost pairing
A car battery replacement, a jump start, or a fob battery that was out too long can make the car forget the fob. Some vehicles let you re-pair a fob yourself with a sequence of key turns and button presses; the procedure is in the owner's manual. Many newer cars require a programming tool. A mobile locksmith carries one and re-pairs the fob at the car, usually in under half an hour.
Cause 3: the fob itself
Buttons wear out, the circuit board cracks after enough drops, the internal blade wears until it won't turn the lock, and water gets in at the beach. A fob that works intermittently or only when squeezed a certain way is on its way out. A locksmith can transfer your car's programming to a new fob shell or a new fob, and cut a new blade, on site.
Causes 4 and 5: interference and the car
Fobs occasionally fail near strong radio sources: some parking structures, certain gas stations, near broadcast equipment. Move the car and try again. If the spare fob also fails and the battery is fresh, the fault is likely in the car: the receiver, an antenna, the start button or a fuse. A locksmith can rule the fobs in or out; a car-side electrical fault is a mechanic's job, and a straight locksmith will say so.
What a replacement costs
Reprogramming an existing fob is the cheapest fix. A replacement remote or smart key programmed at your car, anywhere from the Kearny Mesa dealer row to a UTC parking garage, typically runs $175 to $450 in San Diego depending on the vehicle, often well under the dealer's price and without the tow or the appointment. Some late-model European and luxury cars are dealer-only, and we'll tell you on the phone. See car key replacement and prices.
Written by Mark Hanna, owner and lead locksmith of Action Locksmith San Diego (CA LCO License #7199). Published , last updated . Prices mentioned are typical San Diego ranges; see the prices page for details.
