When the key fob battery dies and it is already dark

What a dead fob feels like

It usually happens in a parking lot, a driveway or a gravel pull out, with a bag in one hand and the vehicle in front of you. You press the button. Nothing happens. You press it again, harder, as if force would help. The doors stay locked, the lights stay dark and the car looks as though it has stopped listening.

Take a breath. A fob that has gone quiet is one of the most common vehicle problems after dark, and in most cases the vehicle itself is fine. What has failed is a small coin cell battery inside a plastic case, and the car has a plan for that situation.

This page walks through that plan in order. Start with the safe place to stand, then the signs that point to the battery, then the backup ways in and the backup ways to start. If none of those work, you will know exactly what to tell the dispatcher.

How a fob talks to the vehicle

A remote fob is a small radio transmitter. When you press a button, it sends a coded signal that the vehicle checks. If the code matches, the receiver unlocks or locks the doors. The code changes with every press in most systems, so a recorded signal cannot be replayed.

A smart fob, used on push to start vehicles, does more. It listens for a low power signal from the car and answers on its own. The car checks the answer when you touch a door handle or press the start button. That constant listening uses more battery than a plain remote, which is why smart fobs often wear out first.

Inside many fobs there is also a chip that holds the identity of the key. That chip can be read at very short range by a coil near the start button, even when the battery in the fob is dead. This is the reason the vehicle often starts when you hold the fob against a specific spot. The chip does not need the battery to be read.

Signs that point to the battery

Fob batteries rarely fail without warning. The range shrinks first. You find yourself pointing the fob at the vehicle from closer and closer. Then you need two presses instead of one. The little light on the fob may dim or stop blinking. On some vehicles a dashboard message tells you the key battery is low.

If you ignored those signs, the failure arrives at the worst time. Cold weather makes it more likely. Batteries lose strength as the temperature falls, so a fob that worked at noon may refuse to work at midnight on a frosty night in the mountain towns of Siskiyou County. Heat can also shorten battery life, especially if the fob lives on a dashboard in the Redding summer sun.

There are other causes that look the same. The vehicle battery may be low. The fob may have been dropped or washed. The fob may have lost its link to the vehicle. The checklist later in this page helps you sort those out before you spend money on the wrong fix.

• The fob works only when held very close to the door.
• The indicator light on the fob is dim, slow or missing.
• Some buttons work and others do not.
• A low key battery message appeared earlier in the week.
• The fob worked earlier in the day and then stopped.

First steps in the dark

Before anything about the lock, look at your surroundings. Is the place lit? Are there people close by? Are you on a road with traffic? If you feel uneasy, move to a lit area and stay near other people. The vehicle can wait. Your safety comes first.

Then try the simple things. Walk to the driver door and try the handle. Try the other doors, including the rear hatch, since a door may have been left unlocked. Look through the window to see whether the fob is in the cabin. If it is in your hand and the doors are locked, go on to the physical key.

If you are with passengers, give each person a simple job. One person watches the surroundings. One looks through the owner manual or the glove box once the door is open. One keeps the phone ready. Calm routines keep tension down, and they stop anyone from wandering off into a dark roadside to look for help.

If you are alone, keep your belongings close and your hands busy with the task, not with the phone screen. Let a friend or family member know where you are and what the problem is. A short message is enough. Then work through the steps one at a time.

Do not keep pressing the button over and over. Repeated presses can wear down a weak battery further, and some systems stop answering for a short time after many failed attempts. Press two or three times, then change approach.

The hidden physical key

Most smart fobs carry a mechanical key inside the case. It is a thin metal blade, often with no plastic head, held in by a small latch. Look for a button or a slide on the fob. Press or slide it and pull the blade out. If you cannot find the release, a thumbnail along the seam of the fob may reveal it.

Many vehicles with this key hide the lock cylinder under a cap on the driver door handle. The cap looks like trim. A small notch on its underside can be lifted with the tip of the blade. Take care not to scratch the paint. Insert the key into the exposed cylinder and turn it to unlock the door.

On some vehicles the alarm may sound when you open the door this way. That is normal. The alarm turns off once the vehicle recognizes the key chip, which happens at the next step. The cap is held by a small tab, and prying it hard can crack it, so work gently and let the blade do the lifting. Once the cylinder is exposed, the key turns just as it would on a car with a traditional door lock. Turn it toward the unlock position and hold it there for a moment, since some vehicles unlock only the driver door on the first turn. Because layouts differ by make, model, year and trim, check your owner manual or call the dispatcher with those details if you cannot find the cylinder.

Starting the vehicle with a dead fob

Opening the door is only half the job. If the fob battery is flat, a push to start vehicle may still run. The standard backup is to hold the fob against a marked spot, often on the steering column, the start button itself, the console or inside a cup holder. The vehicle reads the chip through the case. Then you press the brake and press the start button within a few seconds.

Your owner manual shows exactly where the spot is for your vehicle. Without the manual, try the start button first, since many fobs are designed to touch it. Hold the fob firmly against the button, then press it with the fob in place.

A few habits help at this step. Make sure the vehicle is in park or neutral as the manual requires. Press the brake pedal firmly, because many systems will not start without it. Hold the fob steady and do not move it while you press the button. If nothing happens, shift the fob a little and try again, since the coil that reads the chip has a small reach. Do not repeat this more than a handful of times, as a patient pause is better than a flurry of attempts.

For vehicles with a regular ignition slot, the chip is read when the key is inserted. A dead battery does not matter, because the chip does not rely on it. If the engine still will not start with the metal key in the slot, the issue may be with the chip, the immobilizer or the vehicle battery, and it is time to call.

Other causes that look like a dead fob

A flat vehicle battery is the common look alike. If the door lights do not come on and the dashboard stays black, the problem may be the car battery and not the fob. Our page on a dead car battery and door locks explains how that case differs.

Interference can also silence a fob. Strong radio sources near a building or a utility installation can overwhelm the weak signal. Move a few steps away from the spot and try again. A fob kept in a pocket with a phone or metal items can also be partly blocked.

Physical damage is the fourth cause. A fob that has been dropped on concrete, trodden on, or soaked can have a cracked circuit board or a corroded battery contact. Open the case and look. A greenish crust on the metal contacts points to moisture. Gently cleaning the contacts with a dry cotton swab sometimes brings a fob back, but a fob that has been through water often fails again soon afterward.

Finally, a fob can lose its pairing to the vehicle. This happens rarely, but it happens after a battery change that took too long, after a repair on the vehicle or after the fob is dropped hard. In that case a new battery will not help and the fob needs to be programmed again. A mobile locksmith with programming equipment can do this at the vehicle.

Changing the battery yourself

If you have a spare battery, the change is simple. Most fobs use a flat round cell stamped with a code on its face, and the fob case opens with a small flat tool or a coin. Note which way the battery sits before you remove it. The positive side is usually up. Slide the new cell into place, close the case and test.

Do not touch the flat faces of the new cell with oily fingers if you can avoid it. Handle it by the edges. Do not use a metal tool that can short across the cell. Keep the old cell away from children and pets, since small coin cells are a swallowing hazard.

Check the number stamped on the old cell before you throw it away, and take it with you when you shop. Several cells look alike but differ in thickness, and the wrong one may fit loosely or press too hard on the contacts. If the fob case has a printed battery type on the inside, that is the safest guide. Photograph it so you do not need to open the case again.

If you do not have a spare, you may not need one tonight. Use the backup entry and start steps above to get on your way, and replace the battery in daylight at a place that sells them. A tired fob that still works with a hold against the start button can wait until morning.

When to call a mobile locksmith

Call when the backup steps do not work, when the mechanical key is missing, when the cylinder is hidden and you cannot find it, or when the fob has stopped talking even with a new battery. Call also if the vehicle starts but warning lights stay on, since that may show that the fob and the car are no longer paired.

Redding Mobile Locksmith runs a branded service van with professional tools and programming equipment, and the team serves Shasta and Siskiyou counties. For a fob problem, ask whether the visit can cover entry, a fob battery, reprogramming or replacement, and what information is needed first. The pages on transponder programming and vehicle key replacement describe what these jobs involve.

Expect a few questions. The dispatcher will want to know whether any key at all works, whether there is a second fob at home, and whether the vehicle is parked in a place where a van can reach it. If you are in a rural spot, say what the road is like and whether a gate must be opened. The team can then decide what to bring and what to explain before arrival.

Have the year, make, model and trim ready, along with proof that the vehicle is yours. Key types vary by model and year, so those details decide what is possible on site. See preparing your vehicle information for the call for a short list.

Preparing so it does not happen again

Replace fob batteries on a schedule rather than waiting for failure. If your fob is a few seasons old, change the cell before winter. Keep a spare cell of the right type in a drawer at home, not in the vehicle.

Learn where your backup start spot is while it is daylight and you are calm. Practice once. Take out the hidden key and look at it. Find the cylinder under its cap. That small rehearsal turns a night problem into a familiar routine.

Consider a spare fob. If your only fob fails completely, a replacement from nothing is a bigger job than adding a second key while the first still works. The page on why a spare key matters before you need it explains the reasons. For related situations, see smart key replacement in plain words and push to start vehicles and lockouts.

Common questions