Lost Communication With Gateway "C"

Possible causes

• CommonLow battery voltage or a discharged battery, dropping modules off the bus
• CommonBlown fuse or corroded earth on the supply to gateway "C"
• CommonDamaged, chafed or corroded bus wiring
• CommonWater ingress at the module - these often sit low in the footwell or behind a wheel arch
• PossibleFailed module
• PossibleAftermarket electrical work spliced into the bus
• PossibleModule not coded or configured after a previous repair or replacement

What you might notice

• A large number of fault codes across unrelated systems
• Several warning lights on at once
• Scan tool cannot see whole groups of modules
• Central locking, lighting, wipers or windows behaving strangely
• Battery draining overnight
• Vehicle may not start

What to check, in order

1. Fix this before chasing anything else. When a gateway or body control module is missing, most of the other codes stored are symptoms of this one, and diagnosing them individually wastes a great deal of time.
2. 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.
3. Check whether this code is current or historic. Lost-communication codes are routinely set by a flat battery, a jump start or a battery disconnection, and a historic code straight after one of those events usually records the event rather than a fault.
4. Check the fuses and earth points for gateway "C".
5. Look for water. These modules are commonly mounted in footwells, under seats or behind wheel arch liners, and a blocked drain or a leaking screen seal is a frequent cause.
6. Ask what was done to the car recently. Aftermarket alarms, trackers and tow bar wiring spliced into the bus are a common cause.
7. Record the full code list before clearing anything. After the repair, clear them and see which ones actually come back - usually far fewer than were stored.