Key Not Detected
'Key not detected' is one of the most common security-system warnings on modern vehicles. It can mean the key itself is faulty, but it can also mean the keyless module (CAS, KVM, KESSY, EIS or equivalent) or its antennas, wiring or power supply are at fault. Simply replacing the key is often not the answer.
Common Symptoms
Typical signs of this fault include:
What Could Cause It?
This fault can have several underlying causes — not all of them mean a module has failed:
- Faulty key battery or damaged key
- Keyless module failure (CAS, KVM, KESSY, EIS, etc.)
- Antenna or antenna-circuit faults
- Wiring or connector faults in the keyless system
- Power-supply or earth faults to the module
- CAN/network communication faults
- Software or configuration issues
- Immobiliser or security-system faults
About the Key Not Detected System
Modern keyless systems use a module that communicates with antennas around the vehicle to detect and validate the key's presence and authorise starting. The system involves the key (with a transponder), antennas, the keyless module, the immobiliser and the engine ECU — a chain where any link can cause a 'key not detected' fault.
Is the Control Unit Definitely Faulty?
A keyless module fault is a common cause of 'key not detected', but the module should not be replaced without confirming the key, antennas, wiring and power supplies are all OK. We diagnose the complete chain before recommending any module replacement.
How Is It Diagnosed?
At OBD_PAL, we diagnose the complete system before recommending any replacement. Diagnosis typically includes:
Don't guess — diagnose it properly.
- Diagnostic scan of the keyless and immobiliser systems
- Key and transponder testing
- Antenna and antenna-circuit testing
- Module power-supply and earth testing
- CAN/network communication checks
- Wiring and connector inspection
- Software and configuration verification
Wiring & Electrical Diagnosis
Keyless antennas and their wiring — often routed in door handles, the boot area and the cabin — can suffer from water ingress, corrosion and damage. A fault in an antenna circuit can cause the same 'key not detected' warning as a failed module.
Coding, Programming & Configuration
If a keyless module is replaced, security procedures — key matching, immobiliser pairing and coding — are usually required before the vehicle will start. Some modules can be cloned from the old unit; others need full programming. A second-hand module is rarely plug-and-play.
Component & Control-Unit Replacement
Where a keyless module is confirmed faulty, we carry out the correct replacement, programming and security matching so the vehicle recognises its keys and starts correctly.
Don't Replace Modules Based on Guesswork
A fault code is a starting point, not a diagnosis. Many expensive control units are replaced unnecessarily when the real cause is a sensor, a wire, a power supply or a software issue. At OBD_PAL we diagnose the complete system first — don't guess, diagnose it properly — and only replace a module once it's genuinely confirmed faulty.
Key Not Detected?.
Don't replace expensive parts based on a fault code. OBD_PAL can diagnose the complete system and find the actual cause — then carry out the correct repair, programming or calibration.
This fault guide applies across all makes. For manufacturer-specific electrical diagnostics and module terminology, select your vehicle brand: