Lost Communication With Rain Sensing 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 rain sensing module
• CommonWater ingress at a bumper- or screen-mounted sensor connector
• CommonDamage from a minor knock, a car wash or bumper work
• PossibleDamaged, chafed or corroded bus wiring
• PossibleFailed module
• PossibleModule not calibrated after windscreen or bumper replacement

What you might notice

• The assistance system will not switch on
• Warning message for the driver aid
• Parking sensors silent, or beeping constantly
• Adaptive cruise control unavailable
• Automatic wipers not responding to rain
• Blind spot warning inoperative

What to check, in order

1. Assume the system is off and drive accordingly. Blind spot and parking aids fail quietly, and the danger is trusting one out of habit rather than the failure itself.
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. Ask whether the windscreen or a bumper has been replaced, or whether the car has had a knock. These sensors need calibrating after that work, and an uncalibrated sensor is more common than a failed one.
4. Inspect the sensor and its connector for water and physical damage. Bumper-mounted sensors take the worst of the weather and the car wash.
5. Check the fuses, earths and connector for the rain sensing module.
6. Note how many U-codes are stored. Several at once points at battery, earth or bus wiring.