CAN network

U0231 — Lost Communication With Rain Sensor Module

Severity: low Safe to drive

What U0231 means

Other control modules on the CAN bus are no longer receiving messages from the rain sensor module mounted on the windshield. It controls the automatic wipers and, on some vehicles, automatic headlights, and it normally sends moisture and light data on a regular cycle. When those messages stop, U0231 is stored.

Symptoms

  • Automatic wipers don't work or act erratically
  • Auto headlight mode is affected or unavailable
  • Several warning lamps may light up
  • Features tied to the rain sensor are unavailable

Possible causes

  1. Failed rain sensor on the windshield
  2. Open, short, or chafed CAN bus wiring
  3. Corroded connector or terminals at the module
  4. Power or ground fault at the sensor module
  5. Another faulty module loading down the bus
  6. Aftermarket windshield without a sensor or with poor sensor contact

How to diagnose

  1. Run a full-system scan and map which modules are not communicating
  2. Look for other U-code lost-communication faults that point to a wider bus problem
  3. Inspect the sensor connector behind the mirror for loose pins, moisture, and corrosion
  4. Check for power and ground at the module connector using the wiring diagram
  5. Measure CAN bus resistance and voltages at the diagnostic connector
  6. Inspect the harness for chafing or breaks, especially at flex points
  7. Confirm the windshield and sensor mounting (gel pad) are correct
  8. Disconnect suspect modules one at a time only if the manufacturer's procedure allows it

Common fixes

  • Clean or replace the connector and damaged terminals
  • Repair the power, ground, or CAN wiring fault
  • Replace the rain sensor module
  • Replace a faulty module that is disrupting the bus
  • Install the correct windshield with sensor and code the module if required

Questions and answers

What does U0231 mean?

It means lost communication with the rain sensor module. Other modules on the CAN bus aren't receiving its messages, so auto wipers and related features may stop working.

Can I drive with a U0231 code?

Usually yes, because it doesn't affect the engine or brakes. Operate wipers and lights manually and have it repaired when convenient.

Can a new windshield cause U0231?

Yes. A replacement glass without a sensor mount, or a poorly seated sensor, can interrupt communication. Check the connector and sensor fit first.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.