Car Immobiliser Not Recognising Your Key? Causes and Fixes
When the immobiliser light stays on and the car won't start despite the correct key, the issue could be in the key, the antenna, or the ECU itself.
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Cause 1: Dead Key Fob Battery
If the key's battery is flat, the transponder still works (passive chip) but the car may display an IMMO warning. Try holding the fob directly to the start button or ignition.
Cause 2: Detuned Transponder / Lost Programming
Keys can lose programming due to strong magnetic fields, ECU software updates, or battery disconnection on the vehicle. Reprogramming the key to the ECU resolves this.
Cause 3: Damaged Antenna Coil in the Vehicle
The ignition barrel antenna ring reads the transponder. If this is damaged or unplugged, no key will be recognised. Requires a hardware check.
Cause 4: Failed IMMO ECU
In rare cases, the immobiliser module or ECU itself fails. This requires diagnostic equipment to confirm — Key 2 BHP carries OBD diagnostics for on-site assessment.
What to Do First
Check your key battery. Try the second key if available. If neither works, call Key 2 BHP — we'll diagnose on-site and advise on the fix before charging.
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