How to replace the battery in a car ignition key? Recommendations and tips for replacing the battery in the key fob with your own hands

Types of car keys

If you have problems with the ignition, you shouldn’t immediately paint terrible pictures in your head. Perhaps the problem is the key, and then everything will be limited to replacing the battery. In the case when it is present.

First of all, you need to understand which version of the key is used for a particular car - there are several varieties:

Classic. Both the chip and the microcircuit are absent in this version. Is there a power supply? No. And why does it need a metal blank with threads?
Service. This option has a more complicated device - a transponder chip is available. But the functionality is limited to simply opening the lock. There is no need to wait for remote operation; in most cases there is no battery;
Having an electronic transmitter and a rotating mechanism. The case contains a microcircuit and a transponder that allows you to control the lock at a certain distance. The battery is, of course, installed;
Equipped with a discharge mechanism. Here you need to take a closer look at the product - it can be either with or without a battery;

Smart keys. Present in cars where there is no standard ignition switch - the “start-stop” button works instead. There is a battery - a must.

Why does the immobilizer not see the car key?

Understanding the principle of its operation will help you understand why the immobilizer does not see the key. A working security system unit makes contact with the key, reads the unique code and compares it with the one stored in memory. When it is not possible to read the code or it does not correspond to what is written in the block, the immobilizer blocks the engine from starting.

The main reasons why the immobilizer does not see the original key, and ways to solve them, are collected in the table.

Problems	Cause of occurrence	What to do?
Malfunctions in the power supply of the engine control unit	Low battery charge	Charge or replace the battery
	Broken wiring	Detect and repair the break
	Fuse blown	Inspect fuses, test circuits for short circuits, replace blown fuses
	ECU contacts are bent, loose or oxidized	Inspect the ECU connectors, align and/or clean the contacts
Firmware failure	Damage to controller software files	Reflash the ECU, register the keys or remove the immobilizer
Firmware failure	Control unit memory failure	Repair (resolder the flash and flash the unit) or replace the ECU, register the keys or repair the immobilizer
Physical chip failure and magnetic irradiation	Shocks, overheating, getting the key wet	Start the car with a different key, buy and register a new key
Physical chip failure and magnetic irradiation	Irradiation of a key by an EMR source	Remove the radiation source, start with a different key, replace and register a new key
Drop in battery charge level	Leaving the car with electrical appliances running will cause extreme wear and tear on the battery	Charge the battery or replace it with a new one
Poor antenna-receiver contact	Damage or oxidation of contacts	Inspect the wiring, clean the terminals, restore contacts
Poor antenna-receiver contact	Antenna failure	Replace antenna
Lost communication between immobilizer and ECU	Poor contact, oxidation of connectors	Ring the wiring, clean the contacts, restore integrity
Lost communication between immobilizer and ECU	Failure of the immo block or ECU	Diagnose units, replace faulty ones, flash keys or reset immobilizer function
Malfunction in the power supply circuits of the immobilizer unit	Broken wires, oxidation of connectors	Check wiring, restore integrity, clean connectors
The immobilizer does not recognize the key in cold weather	Low battery	Charge or replace the battery
	The immo bypass unit in the security system with auto start is faulty	Check the immobilizer bypass, the chip installed in it, and the bypass antennas
	Freezing of electronic components	Warm up the key
The battery in the active key is discharged	Battery life expired	Replace battery
The immobilizer bypass unit does not work or does not work correctly	Bypass block failure	Repair or repair the bypass block
	Label offset in the crawler	Correct the label

If the immobilizer does not see the key well, the reasons are most often poor contact, mechanical damage to the block or chip, or low supply voltage. You need to pay attention to the problems listed above when your car displays an immobilizer error after an accident.

In some cars, after an accident, the safety system may block the fuel pump. In this case, the protection must be deactivated. The method is different for each model, for example, on a Ford Focus you need to press the button to turn on the fuel pump in the niche near the driver’s left foot.

Software disabling the immobilizer from the ECU

Situations where the immobilizer does not always see the key due to the firmware are rare. Usually, if software fails, it fails irrevocably. The malfunction can be resolved by rebinding the key or software disabling the immobilizer.

Owners of Ford, Toyota, Lexus, Mitsubishi, SsangYong, Haval and many others equipped with a non-standard alarm with auto start in the presence of a lineman may encounter cases when, when cold weather sets in, the immobilizer does not see the key. Therefore, you need to start troubleshooting in the bypass block. If the tag is equipped with its own battery, you need to check its charge level, as it quickly drops in the cold.

Most keys for cars with an immobilizer are passive: they do not have batteries, and the power is supplied by induction from a coil installed in the area of the car lock.

To avoid problems with the immobilizer, it is recommended to take the following precautions:

do not disassemble the key, immobilizer and ECU;
do not throw the keys, do not get them wet or expose them to electromagnetic waves;
use high-quality bypass units when installing non-standard alarm systems with auto-start;
when buying a used car, ask the owner for all the keys, a piece of paper with the immobilizer code written down for flashing new ones, and also clarify information about the features of the installed alarm (its model, availability of immo bypass, location of the service button, etc.).

When purchasing a used car with only one main key, it is not possible to link new chips to the unit. Only replacing the immobilizer or ECU will help. The costs of these procedures can reach tens of thousands of rubles!

How to understand that the battery in a car key is dead

If the battery fails, the key will not be able to start the car, and sometimes even provide entry into it. There is only one way out - change the battery. As a rule, the fact that “hour X” is about to come is indicated by the corresponding icon flashing on the panel. Appeared? It's time to disassemble the key.

Opening a car with a dead key is not an easy task: modern models do not even have the ability to do this mechanically. The problem will be solved by the so-called emergency element, which allows you to open the car and start it.

The emergency system of each brand is organized in a special way and the description of each is a subject for a separate discussion.

How can you tell if the battery is low?

The range of a key operating remotely has been reduced, and significantly.
A corresponding notification appears on the instrument panel.
Car doors don't want to open.
The vehicle cannot be started.

How to start a BMW and Mini engine if the key fob is dead?

In some models of BMW and Mini cars, in order to start the engine, you need to insert the key fob into a special connector, which is located next to the stop-start button.
If the key fob battery is low, when you insert it into the connector next to the stop start button, the car's electronic system recognizes the electronic key fob. If your BMW and Mini car model does not require inserting the key fob into a special slot, then you need to keep the car key in the area of the steering column, as indicated by the arrow in the picture (see photo). Next, you need to press the stop-start button and hold it for ten seconds while keeping the brake pedal depressed. Note : If you are unsuccessful in trying to start the engine using the method described above, then there may likely be residual pressure in the brake system of your car. In this case, a warning symbol may appear on the dashboard.

In this case, try again to start the engine by pressing the brake pedal as hard as possible while pressing and holding the stop-start button for 10 seconds.

Attention. Press the brake pedal until the warning message to press the brake pedal disappears on the instrument panel.

Source

Which battery to buy

The golden rule for a motorist is not to buy a cheap “pill” for the key. This will cause the replacement to be made much more often, and problems may even arise in the system.

It is better to choose a battery similar to the one that was already installed in the key or opt for a well-known high-quality analogue.

In most cases, the car key is equipped with one of seven types of batteries. Some models have batteries that are recharged automatically - when the key is in the lock and the car is moving. But more often the battery is still a classic three-volt “pill”.

You can find out which one:

After studying the operating instructions;
By asking a question to an official dealer;
Looking at thematic forums;
Having disassembled the key body.

We disassemble the Ford Focus 3 ignition key fob

From 2012 to 2015, the key began to be produced without a collapsible part. This is not to say that there is no analog complement. It is there, but it is no longer thrown out, but hides in the otter.

We will replace the battery this way. To do this, press the buttons on the sides of the key.

The lid will open; inside we will see an analog key (iron part).

But there is no battery here, but I would like to see it)

Now, from the side of the button, we pry the box with a screwdriver, splitting it into pieces. Then the key will remain intact, without marks on the sides.

Having divided it in the area of the buttons, we go to the back, there is a notch there, we also turn it with a screwdriver. The body is completely divided.

We see a battery in one of the halves, take it out and change it. We collect.

For those who lose such a key, it costs 8,000 rubles from the officials.

We act quickly

Many car enthusiasts are inclined to simply go to a workshop and replace the battery there, but you can complete this simple task yourself. True, you will have to act like a sapper - that is, carefully and quickly, and therefore it is better to read the instructions in advance, having built a procedure in your head.

If the chip key does not have power, the code in the anti-theft device begins to gradually erase - that is, the immobilizer will not be able to do so for more than five minutes without a battery, otherwise the key will have to be synchronized with the central locking control key fob.

Can't you start a car with keyless entry with a dead key fob?

In fact, everything is not so simple. Firstly, as we already said, the doors can be opened with a key. You know those flip keys on some car models? But even if it is not in the remote control, it is still there. So to speak, an emergency mechanical option. We wrote about this in detail here:

We find the emergency keyhole, first seal it with WD-40 (since no one uses it, the mechanism may rust), and then, using the instructions, we open the car.

Key disassembly procedure

Car keys can have different bodies. To disassemble such a product, you should:

Study the instruction manual - there is a diagram according to which the key is disassembled;
As a rule, the case consists of two halves, which can be separated by prying the latch with a thin object (knife blade);
Sometimes a small screw is used as a fastener - in this case you will need a screwdriver;

The battery is sometimes located under a special cover. And this makes the task much easier - you don’t need to disassemble the key fob - you just need to move it, pressing lightly.

Once you have access to the battery, remove the old battery using tweezers and place a new one in its place. Then the car key body is assembled in the reverse order.

Is it possible to start a car if the immobilizer has gone off?

If the immobilizer no longer sees the key, there are a number of ways to disable the lock. First you should try the spare key. If it is not available or also does not work, other methods of bypassing the protection will help. The situation is easiest with older models without a CAN bus. Options for launching them are outlined below.

Chip in immobilizer key

Using an additional key

If the immobilizer key has become loose, but you have a spare one, use it. Most likely the engine will start with a different mark. In this case, you can try to re-bind the “fallen off” main key using a training key, or buy a new one and bind it.

If you have an alarm with auto start, if the immobilizer does not work, you can start the car with the key from the lineman. You can find it by removing the plastic trim from the ignition switch and finding the antenna coil, the wire from which leads to a small box. In it, installers hide a spare key or a chip from it, which sends a signal to the security unit.

After removing the chip, autostart will not work.

Bypass using jumpers

On cars without a CAN bus, simple immobilizers are used to control on-board electronics, for example, Opel Vectra A, which are easy to bypass. To run such a machine you need:

How to disable the immobilizer using jumpers on an Opel Vectra: video

How to disable the immobilizer using jumpers on an Opel Vectra:

Find the immo block in the front panel.
Find its circuit diagram or disassemble the unit and, by testing, identify the contacts responsible for blocking the fuel pump, starter and ignition.
Use a jumper (pieces of wire, paper clips, etc.) to close the corresponding contacts.

Using jumpers it is also sometimes possible to deactivate the immobilizer on older VAZ models such as 2110, Kalina and others.

For cars where the immo block is hardcoded in the ECU firmware, this method will not work.

Installing the crawler

If the immobilizer does not see the key, and the above bypass methods are not available, you can install an immobilizer bypass. There are two types of such devices:

Immobilizer bypass circuit

Remote crawlers . A remote crawler is usually used to install an alarm system with auto start. It is a box with two antennas (receiving and transmitting), which contains a spare key. How to connect the immobilizer bypass is decided by the car alarm installer, but most often the unit is located in the front panel.
Emulators . An immobilizer emulator is a more complex device that contains a chip that simulates the operation of a standard protection unit. It connects to the wiring of the immo block and sends unlocking signals to the ECU via the CAN bus. Thanks to the emulator, you can start the engine even with an unchiped duplicate key.

In order to do without keys at all, you need the second option. Such emulators are relatively inexpensive (1-3 thousand rubles), and their installation allows you to start the car without an immobilizer.

The use of crawlers and emulators makes life easier for the driver, but reduces the degree of protection of the car from theft. Therefore, autostart should only be installed in conjunction with reliable, high-quality alarm systems and additional protection systems.

Coded immobilizer deactivation

The answer to the question “is it possible to start a car without an immobilizer, a lineman and a spare key?” depends on the presence of a special password. The PIN code is entered as follows:

Standard immobilizer keyboard in Peugeot 406

Turn on the ignition.
Depress the gas pedal and hold it for 5–10 seconds (depending on the model) until the immobilizer indicator goes out.
Use the on-board computer buttons to enter the first digit of the code (the number of presses is equal to the number).
Press and release the gas pedal again, then enter the second digit.
Repeat steps 3–4 for all numbers.
Start the unlocked car.

On some cars, the central locking control button on the remote control may be used to perform the procedure.

Replacing the control unit

If none of the ways to bypass the immobilizer without a key helps, all that remains is to change the blocks. At best, you can only replace the immobilizer unit by attaching new keys to it. In the worst case, you will have to change both the ECU and the immo block. The procedure for connecting and disconnecting the immobilizer depends on the car.

For a number of models, there are firmwares with deactivated protection. They can remove the immobilizer lock permanently. After flashing the ECU, the engine starts without interrogating the protective unit. But since it becomes much easier to start a car with an unchip key, it is advisable to use firmware without protection only if there is a good alarm system.

Restoring an old battery

Sometimes some are faced with a situation where the battery is obviously dead, and it is not possible to purchase a new one right away. The only way out is to try to “resurrect” the battery, which has obviously become obsolete and is located in the key fob.

First you need to remove it from there and then begin to act.

The simplest way to “cheer up” the battery for a while is heating. But the main thing here is not to overdo it - extreme temperatures threaten an explosion.
In some cases, the “old-fashioned” method also helps - you need to knock on the battery, intensifying the chemical reactions occurring inside.
You can try to recharge the battery from other power sources - you will need a couple of wires and at least minimal skills. We should not forget: during such blasphemous manipulations the battery will heat up.

But these actions are only suitable in a situation like “alone in the taiga, a hundred kilometers from the nearest store.” Ideally, every motorist needs to have a spare battery with him - you never know.

The service life of batteries, even when not in use, is limited, and therefore it is periodically necessary to examine the “reserve” to see if the date of possible use has expired.

Having studied all of the above, it becomes clear: there is nothing complicated in replacing the battery of a car key, which is so scary for many - the main thing is to understand the scheme for disassembling the case and remember that the time of action is limited.

Charging the battery

In cases where the first method does not work, you can use the following three methods:

conduct battery current from the remote control from an external source. The 12 watt battery can be recharged using a battery and wires;
If we are talking about a 3 watt battery, then you can use a mobile device as a power source.

Photo instructions for replacing the battery in a car key

Types of batteries for alarms and their characteristics

Depending on the type of key fob (main, with a display, or auxiliary, without a screen), the device can use different types of batteries:

special batteries class 27A;
lithium batteries 2032;
2025 batteries.

Special batteries

Description of the main technical parameters of class 27A devices:

Battery length is 2.8 cm, diameter is 0.8 cm;
the weight of a suitable charger, regardless of voltage, varies around 7-12 grams;
the parameter of the nominal capacity consumed by the battery is 20 mAh;
devices belong to the class of 12-volt batteries;
The operating temperature range of the batteries is from -30 to +70 degrees on average.

The channel “Gatherings at Lehi’s” briefly talked about the characteristics and parameters of batteries for alarms related to the A27 standard.

Lithium batteries 2032

The main parameters of devices for the remote control of the “signaling” machine 2032:

By size, batteries belong to the disk category;
The devices are based on lithium-manganese electrolyte;
the use of power supplies is allowed in remote controls for car anti-theft systems with a voltage of 3 volts;
the temperature range at which the devices can be used and stored is from -40 to +60 degrees;
CR2032 class batteries have a diameter of 20 mm and a thickness of 32 mm;
The current consumption is about 210 mAh.

Lithium 3-volt alarm batteries are often used in anti-theft systems from the manufacturer Starline.

Batteries 2025

Description of the main parameters of these power supplies:

The battery current consumption is 150 mAh;
height and width of batteries - 2 cm;
weight of one battery - 2.5 g;
The power source is based on lithium electrolyte;
The battery is designed for use in communicators operating with a voltage of 3 volts.

Photo gallery

Photos of batteries of different classes:

Battery type CR2025 Power supply standard CR2032 Battery class A27