Fault Diagnosis · Mobile
Car Immobiliser Repairs
Diagnosed Honestly, Fixed at Your Car
Warning light on, engine won't start, fault code in the dash? Most immobiliser problems have a simple cause and a £50–£150 fix — the dealer will tell you it needs a whole new module. We diagnose the actual fault first, then tell you what it really needs.
Don't pay for a whole new module
Main dealers have one workflow for immobiliser faults: replace the module. We'll diagnose the actual fault first — most of the time it's a £50 antenna ring, a £30 wiring repair, or a £40 re-sync. The dealer would have charged you £500+ for the same fix.
Common Immobiliser Faults
Six of the most common faults we see, ranked by how often we get called out for them.
Transponder antenna ring failure
The ring around the ignition that reads the key chip can crack, corrode, or detach from the wiring. Symptoms: car starts sometimes, sometimes not. Repair: replace the ring (£40–£80 part). Common on Ford Focus, Vauxhall Astra, VW Golf Mk4/5.
Immobiliser ECU fault
The immobiliser module itself can fail — water ingress, vibration damage, capacitor failure. Symptoms: warning light on, no crank, fault code stored. Repair: module replacement and coding (£200–£450 depending on the car).
Wiring / connector fault
Corroded connectors, broken wires, water ingress in the footwell can all knock out the immobiliser. Symptoms: intermittent starting, usually after rain. Repair: clean/replace connectors, repair wiring (£80–£180).
Key not authorised
The car's immobiliser has lost sync with the key. Symptoms: car won't start, light is on, but the key works the door locks. Repair: re-sync the key to the immobiliser (£40–£90).
Fault code in ECU
Stored fault codes like P0513, B1342, or 'transponder signal missing' need diagnosing before they can be repaired. We plug in, read the code, and tell you what the actual fault is.
BSI / BCM fault
On French cars (Peugeot, Citroën, Renault) the BSI (Built-in Systems Interface) is the equivalent of a BCM and can lose its coding. Symptoms: random electrical faults, immobiliser light. Repair: BSI re-coding, sometimes full replacement.
Frequently Asked Questions
Immobiliser Light On?
Call us with the reg number. We'll diagnose the fault, give you an honest price, and fix it on the spot if we can.
Call 01723 817140