U0427: Invalid Data Received From Vehicle Security Control Module
What to do
The car drives and starts normally — this is the alarm rather than the immobiliser. Expect an alarm that goes off by itself, refuses to set, or behaves unpredictably.
Before assuming a fault, rule out the things that genuinely set alarms off, because none of them is a fault at all: a pet or anything moving inside, an air freshener swinging from the mirror, a window left slightly open so air circulates, or a soft-top flexing in the wind. Interior sensors are supposed to react to movement.
Then check the doors, boot and bonnet shut properly. A switch reporting a door as open when it is not makes the alarm think the car is being broken into — and that same fault flattens batteries, because a car that thinks a door is open never powers down.
If an alarm, tracker or immobiliser was fitted after you bought the car, start there. Added security equipment is wired into the vehicle's own circuits and is far more likely to be the problem than the factory system.
What this code means
The vehicle security module is broadcasting data that cannot be accepted as true. See U0400 for the family's framing and U0426 for the immobiliser, which is a related but distinct system.
The distinction between the two is worth being clear about, because it decides whether the car will start. The immobiliser stops the engine running for the wrong key. The security module is the alarm — it watches doors, bonnet, boot, interior movement and the glass, and it makes noise. So a security module fault is normally an alarm problem, not a starting problem.
The symptom that brings people to this code is usually an alarm that goes off by itself, and that is worth taking seriously as a diagnosis rather than as a nuisance: the alarm is reacting to an input it is being told about, and an input reporting something impossible is exactly what triggers it.
The inputs most often responsible are ones the corpus has already described. A door or bonnet switch reporting a state that cannot be true — see U0215 — makes the alarm believe the vehicle is being opened. And interior movement sensors are set off by things that genuinely move: a pet left inside, an air freshener swinging, a window left slightly open letting air circulate, or a soft-top flexing in wind. Those are not faults, and eliminating them costs nothing.
A separate consequence worth flagging is the battery. An alarm system that keeps waking the vehicle, or that cannot arm and therefore never lets it sleep, draws far more than a parked car should — which is the flat-battery mechanism at U0215 arriving by a different route.
And the standing point about aftermarket security equipment applies here more than anywhere: an added alarm, tracker or immobiliser is spliced into the vehicle's own circuits, and it is the first suspect rather than the last when the security system misbehaves.
Likely causes
Start here
- Faulty aftermarket alarm or immobiliser installation · moderate
- Corroded or loose connector · easy
- Water ingress into the module connector · moderate
Less common
- Faulty body control module · specialist
- Damaged data bus wiring · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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