Lost Communication With Vehicle Security Control Module

Possible causes

• CommonLow battery voltage or a discharged battery, dropping modules off the bus
• CommonBlown fuse or corroded earth on the supply to the vehicle security control module
• CommonDamaged wiring at the steering column or ignition ring aerial
• PossibleCorroded or water-ingressed connector
• PossibleFailed module
• PossibleModule or key not coded to the vehicle after a previous repair
• PossibleAftermarket alarm or tracker interfering with the system

What you might notice

• Engine turns over but will not start
• Immobiliser or key warning light on
• Key not recognised
• Central locking or alarm behaving unpredictably
• Alarm sounding for no reason
• Remote locking not working

What to check, in order

1. Do not switch the engine off far from home until this is fixed. An immobiliser fault that lets you start today may not let you start again, and this is the most common way this fault strands people.
2. Keep the spare key and any mechanical key blade with you.
3. Check battery voltage and state of charge before anything else. A weak or failing battery drops modules off the bus and sets lost-communication codes with no wiring fault at all - this is the single most common false lead in this whole family.
4. Try the spare key. If one key works and the other does not, the fault is the key rather than the module.
5. Check the fuses and earths for the vehicle security control module.
6. Ask whether an aftermarket alarm, tracker or immobiliser has been fitted. These are frequently spliced into the same circuits and are a common cause.
7. Expect security-related repairs to require proof of ownership. Coding these modules is deliberately restricted, and that is a feature, not an obstruction.