Transponder Key London
Replacement transponder keys cut and programmed on-site for all makes and models across London. From £120 + VAT — no dealer, no towing, no waiting days. Mon–Fri, 8am–6pm.
Every car built since around 1995 uses a transponder key. The small chip inside the key head is what allows your car to start — the physical cut alone is not enough. If you lose a transponder key, or buy a replacement key blank from a hardware store, the car will not start until that chip is programmed to match your car's immobiliser. Car Locksmith London provides transponder key cutting and programming on-site across all London boroughs, covering every chip type and every car make.
How a Transponder Key Works
Antenna Ring Sends Signal
When the key is inserted, the immobiliser coil around the ignition barrel sends a low-frequency electromagnetic field that powers the transponder chip — no battery required.
Chip Responds with Code
The chip broadcasts its unique encrypted identification code back to the antenna ring. Rolling-code chips generate a new code each time — this is why cloning doesn't work on modern vehicles.
ECU Validates and Releases
The ECU or immobiliser module checks the received code against its stored values. If matched, the immobiliser disables itself and fuel injection is allowed. If not matched, the engine cranks but will not fire.
Why Transponder Keys Fail or Need Replacing
- 🔑 Key lost or stolen — requires a full replacement key to be cut and programmed
- 💧 Water damage — chip can fail if the key is submerged or exposed to moisture
- 💥 Physical damage — key head cracked or broken, chip damaged
- 🔋 Programming lost — chip de-programmed if battery disconnected during programming attempt
- 🛑 Worn chip — older transponders can fail after years of use
- 🔧 Dealer error — incorrectly programmed or programmed to wrong vehicle
Chip Types We Programme
We carry programming equipment covering every transponder chip type used in UK-registered vehicles:
Texas Instruments
NXP / Philips
Megamos / EM Microelectronic
NXP Hitag
Makes We Cover
Pricing
All prices exclude VAT. Fixed price quoted before we start.
Frequently Asked Questions
What is a transponder key?
A transponder key has a small microchip embedded in the plastic head. When you insert the key and turn the ignition, the immobiliser antenna ring sends a low-frequency signal that wakes up the chip. The chip replies with a unique encrypted code. If the code matches what the car's ECU expects, the immobiliser is disabled and the engine starts. Without the correct chip response, the car will not start regardless of whether the key cuts are correct.
My car starts but the immobiliser light stays on — is this a transponder fault?
A persistent immobiliser warning light after starting usually means the transponder chip was recognised but there's a stored fault in the system — often a previously programmed key that wasn't correctly deleted, or a new key that wasn't fully programmed. We can read the immobiliser fault codes and resolve this on-site in most cases.
Can you clone a transponder key from an existing key?
For some older fixed-code chip types (e.g. ID46 before rolling code was introduced, or fixed ID4D), cloning is possible — we copy the chip data to a blank. For rolling-code chips (Hitag Pro, Megamos AES, Hitag AES) used in most modern cars, cloning is not possible and the car must be programmed via OBD or EEPROM. We'll confirm which method applies to your vehicle when you call.
Do you programme transponder keys for prestige cars like BMW and Mercedes?
Yes. BMW use Hitag 2, Hitag Pro, and AES chips depending on generation. Mercedes use Infrared, Hitag 2, and AES. We carry dedicated programming tools for both marques including all E-Class, C-Class, S-Class, 3 Series, 5 Series, 7 Series, and X-series generations.
How long does transponder key programming take on-site?
Simple OBD transponder programming typically takes 20–40 minutes. If the vehicle requires EEPROM or module removal, expect 1–2 hours. We'll give you an accurate estimate for your specific vehicle when you call.
How much does a replacement transponder key cost?
Transponder key replacement starts from £120 + VAT for a basic key. Remote/flip key transponders are typically £150–£250 + VAT. All prices exclude VAT and are fixed — quoted before we start.