A car immobiliser is not working when the car no longer reads the chip in the key, and a spare key, a new key fob battery or a charged car battery clears most faults before any repair.
A car immobiliser is an electronic security system that blocks the starter, the fuel or the ignition until the car reads the correct code from the chip in the key. The system fails when that code is not sent, not received or not accepted. Six signs show the fault, five checks at the car clear the simple cases, and seven causes explain the rest, three in the key, one in the battery and three in the car. An auto locksmith recodes or replaces a key at the car in 30 to 60 minutes, and car immobiliser repair costs £60 to £250 in the UK where the key is at fault. Every new car sold in the UK since October 1998 has an immobiliser, so the fault reaches every make.
A reset, the cost, an easy fix, a key not detected, a flat car battery, a key fob battery, a car that refuses to start, starting with a fault, a bypass, the dashboard messages, water damage, repair time, a new key, a locksmith and the red car with a key light raise fifteen further questions.
The list below gives four key takeaways on a car immobiliser not working.
- A spare key that starts the car places the fault in the main key.
- An engine that starts and cuts out within two seconds is the clearest sign of an immobiliser fault.
- A flat car battery corrupts the key check and is ruled out with a charge.
- An auto locksmith recodes the key at the car, and a fault inside the engine control unit goes to an auto electrician.
Which signs show a car immobiliser not working?
Six signs show a car immobiliser not working, and an engine that starts and cuts out within two seconds is the clearest one. The list below gives the six signs.
- The engine starts, runs for one or two seconds and cuts out.
- The engine cranks on the starter and never fires.
- The security light, a car with a key or a padlock, stays on or flashes fast with the ignition on.
- The dashboard shows a message that names the key or the immobiliser.
- The remote locks and unlocks the doors while the engine refuses to start.
- The car starts on some days and refuses on others.
The first two signs appear with a healthy battery and bright dashboard lights. A car immobiliser not working leaves the starter and the lights normal, which separates the fault from a flat battery. Five checks at the car come next.
Which 5 checks fix a faulty car immobiliser?
Five checks fix a faulty car immobiliser in the simple cases, and the spare key is the first and the most telling. The list below gives the five checks in order.
- Try the spare key, since a spare that starts the engine places the fault in the main key.
- Fit a new coin cell, usually a CR2032, in the key fob of a keyless car.
- Hold the fob against the start button or the marked spot on the steering column, where the car reads the chip at close range.
- Remove other chipped keys and fobs from the keyring, since a second chip confuses the reader.
- Charge or jump start a car battery under 12 volts, then lock and unlock the car once with the key.
A pause of 10 to 15 minutes follows several failed starts on many cars, since repeated attempts trigger a temporary lockout known as anti theft mode. A faulty car immobiliser that survives all five checks has a cause inside the key or the car.
Why does a car immobiliser stop working?
A car immobiliser stops working because the code from the key is not sent, not received or not accepted by the car. The list below gives seven causes, three in the key, one in the battery and three in the car.
- A flat battery in the key fob stops a keyless car sensing the fob at normal range.
- A damaged transponder chip, cracked by a drop or soaked by water, sends no code at all.
- A key that has lost its coding, often after a flat car battery or a battery change, sends a code the car no longer accepts.
- A weak car battery drops the voltage during the key check and corrupts the reading.
- A failed antenna ring, the reader coil around the ignition barrel, receives no code from a good key.
- Corroded wiring or water in the cabin breaks the line between the reader and the control unit.
- A fault in the engine control unit (ECU) or the body control module loses the stored key data.
The three key causes are the most common and the cheapest to repair. The three car causes give the same signs with every key, which is how a car immobiliser fault is traced. Each cause has symptoms that separate it from other starting faults.
Which symptom separates an immobiliser from other faults?
The security light and the starter separate an immobiliser from other faults, and a normal starter with a flashing security light points to the immobiliser. The table below compares six symptoms of a car that refuses to start.
| Symptom | Likely fault | Next step |
|---|---|---|
| Dim dashboard lights and a rapid clicking | Flat car battery | Charge or jump start the battery |
| One loud click and no crank | Starter motor | Book a garage test |
| Normal crank, no start and a flashing security light | Immobiliser not reading the key | Try the spare key |
| Engine starts and cuts out within two seconds | Immobiliser rejecting the key code | Call an auto locksmith |
| Spare key starts the car and the main key fails | Chip or coding of the main key | Recode or replace the main key |
| Both keys fail in the same way | Antenna ring, wiring or control unit | Book a diagnostic scan |
Rows three to six are immobiliser faults. A car immobiliser not working keeps the starter and the lights healthy, so a dead dashboard points away from it.
Who repairs a car immobiliser fault?
An auto locksmith repairs a car immobiliser fault on the key side, and an auto electrician or a main dealer repairs the antenna ring, the wiring and the control unit.
The key side covers a dead chip, a key that lost its coding and a lost key. Pairing a key to the immobiliser is car key programming, and the work happens at the car with a diagnostic tool on the OBD port. The locksmith reads the fault codes, tests the chip, pairs the key and starts the engine before leaving. ADC Locksmith Liverpool carries out Liverpool car key programming from £60 with no call out fee and no VAT, usually within the hour, 24 hours a day. Craig Evans holds SERMI approval, the accreditation for access to the security data of the car maker, and checks photo ID and proof of ownership first. A scan that places the fault in the car is reported to the driver, who then books an auto electrician with the fault codes in hand.
How much does car immobiliser repair cost?
Car immobiliser repair costs £60 to £250 in the UK where the key is at fault, and £150 to £1,500 where the fault sits in the car. The table below compares six repairs by price.
| Repair | Typical UK price | Who does it |
|---|---|---|
| New key fob battery | £2 to £5 | The driver |
| Key recoded to the immobiliser | £60 to £150 | Auto locksmith |
| New chipped key cut and programmed | £80 to £250 | Auto locksmith |
| Antenna ring replaced | £50 to £150 | Auto electrician |
| Engine control unit repaired | £150 to £400 | Electronics specialist |
| Engine control unit replaced and coded | £500 to £1,500 | Main dealer |
Most quoted repairs fall between £100 and £180, since the key causes most faults. ADC Locksmith Liverpool gives a fixed price on the call, before travel.
What stops a car immobiliser failing again?
Five habits stop a car immobiliser failing again, and a second programmed key is the one that prevents a stranded car. The list below gives the five habits.
- Keep a second programmed key, so one failed chip never strands the car.
- Replace the key fob coin cell every two to three years.
- Keep the key dry and away from drops, since the chip sits in the plastic head.
- Hold the car battery above 12 volts with a regular run or a trickle charger.
- Carry one chipped key on the ring at a time.
A key that takes two attempts to start the car is the early warning. A recoded or replaced key at that stage costs less than a recovery after the car immobiliser stops working.
What else do drivers ask about immobiliser faults?
Drivers ask about immobiliser faults in fifteen further questions on a car immobiliser not working. A reset, the cost, an easy fix, a key not detected, a flat car battery, a key fob battery, a car that refuses to start, starting with a fault, a bypass, the dashboard messages, water damage, repair time, a new key, a locksmith and the red car with a key light are the fifteen topics, and the questions below answer each one.
Frequently asked questions
How does a car immobiliser reset?
A car immobiliser resets on many cars with the key held at ignition on for 10 to 15 minutes.
Three methods bring a car out of anti theft mode, and a failed chip resists each one.
How much does it cost to fix a car immobiliser?
To fix a car immobiliser costs £60 to £250 where the key is at fault.
A repair inside the engine control unit costs £150 to £400, and a dealer replacement costs £500 to £1,500.
Is a car immobiliser fault an easy fix?
Yes, a car immobiliser fault is an easy fix in most cases, since a new fob battery or a recoded key cures it.
A fault inside the engine control unit takes a specialist and more time.
Why is the immobiliser not detecting the key?
The immobiliser is not detecting the key because the chip is damaged, the key has lost its coding or the antenna ring has failed.
A spare key that works places the fault in the main key.
Does a flat car battery cause an immobiliser fault?
Yes, a flat car battery causes an immobiliser fault, since low voltage corrupts the key check.
A full charge clears most cases, and a key that stays rejected has lost its coding.
Does a weak key fob battery affect the immobiliser?
Yes, a weak key fob battery affects the immobiliser on a keyless car, which stops sensing the fob.
A dead battery in a key fob leaves a bladed key starting the car, since that chip draws no power.
Does a faulty immobiliser stop a car starting?
Yes, a faulty immobiliser stops a car starting, since the system blocks the starter, the fuel or the ignition.
The doors, the lights and the radio keep working. The guide to an immobiliser light flashing explains the security light.
How does a car start with a faulty immobiliser?
A car starts with a faulty immobiliser on the spare key, or with the fob held against the start button.
No safe trick starts the car past a failed chip, so the key is recoded or replaced.
Is bypassing a car immobiliser safe?
No, bypassing a car immobiliser is not safe, since the car then starts for any thief with a copied blade.
Motor insurers expect a working immobiliser, and a bypass puts a theft claim at risk.
What does an immobiliser fault show on a Ford or Peugeot?
An immobiliser fault shows on a Ford as Immobiliser malfunction, service now, and on a Peugeot as Electronic immobiliser fault.
A Mercedes shows the fault as a key that turns with no response from the ignition switch.
Does water damage a car immobiliser?
Yes, water damages a car immobiliser where it reaches the key chip, the reader wiring or the control unit.
A leak into the cabin and a key through the wash are the two usual routes.
How long does a car immobiliser repair take?
A car immobiliser repair takes 30 to 60 minutes at the car where the key is recoded or replaced.
A control unit sent away for repair takes several days.
Does a new key fix an immobiliser fault?
Yes, a new key fixes an immobiliser fault where the spare key starts the car and the main key fails.
Two keys that fail in the same way point to the car, where a new key changes nothing.
Does a locksmith fix a car immobiliser?
Yes, a locksmith fixes a car immobiliser fault on the key side, with the chip tested and the key recoded at the car.
ADC Locksmith Liverpool starts from £60 with no call out fee.
What does the red car with a key light mean?
The red car with a key light is the security indicator of the immobiliser, and a slow flash with the car off is normal.
A red car with key symbol on a Nissan stays on where the key is rejected.
Based in Liverpool and still stuck?
ADC Locksmith Liverpool repairs, programs and replaces car keys at the roadside across Liverpool and Merseyside, usually on the same day. Craig Evans holds SERMI approval and a 5.0 rating from 341 Google reviews. A call to 07731 544220 brings a fixed price before Craig travels.
Call 07731 544220