Code
U0231
HYUNDAI
U — Network/User
Lost Communication With Rain Sensing Module
Views:
UK: 18
EN: 92
RU: 25
AI status
Completed
Completed
100%
Causes
- Open or short in CAN bus wiring between RSM and network gateway/module
- Poor power or ground to the Rain Sensing Module
- Corroded, loose or water-damaged connector at the RSM
- Blown fuse or supply circuit fault for the RSM
- Faulty Rain Sensing Module (internal failure)
- Software/firmware mismatch or module addressing error after replacement
Symptoms
- Automatic wipers (rain sense) inoperative or disabled
- Warning message or DTC indication on cluster for rain sensor or communication fault
- Intermittent wiper operation or false activations
- Other modules report related communication errors or display multiple U-codes
- No RSM listed in module scan or module shows as not responding
What to check
- Use a diagnostic scanner to read all stored U-codes and freeze frame; note whether RSM appears on the network scan
- Visually inspect RSM and harness at windshield area for water ingress, corrosion, or physical damage
- Check related fuses and power supply circuits for the RSM
- Verify good chassis/engine ground and module ground continuity
- Check connector pins for bent/corroded pins and verify proper seating
- Attempt communication to the RSM with a scanner; note if it responds intermittently or not at all
Signal parameters
- CAN bus idle voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (recessive)
- Dominant state voltages: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (during activity)
- Differential voltage when active ≈ 2.0 V
- Bus termination: approx. 60 ohms between CAN_H and CAN_L across the network
- Module supply: ~12 V at RSM power pin with key on; good ground continuity to chassis
Diagnostic algorithm
- Connect a capable scan tool and confirm U0231 and any related codes; record freeze-frame and last-clear info.
- Verify whether the Rain Sensing Module is listed/recognized by the scan tool. If it does not respond, continue with physical checks.
- Visually inspect the RSM, its mount area and harness for water intrusion, cracked housing, or connector corrosion. Repair or replace damaged connectors as needed.
- Check fuses and supply circuit for the RSM; verify ~12 V at the module power terminal with key on and good ground at ground terminal.
- With ignition on, measure CAN_H and CAN_L at the RSM connector: verify recessive voltages (~2.5 V each) and observe bus activity while operating other modules; use an oscilloscope if available.
- Check network continuity/termination: measure resistance between CAN_H and CAN_L (approx. 60 ohms). Inspect for shorts to battery or ground on each CAN wire.
- If CAN signals are present at the network but absent at the RSM connector, trace wiring back for opens, shorts, or damaged sections; repair harness or connector.
- Disconnect any aftermarket devices tied into the CAN bus and retest communications.
- If wiring and power/ground are good but the RSM still does not respond, consider reflashing/updating module software per Hyundai service procedures.
- Replace the Rain Sensing Module only after confirming wiring, power/ground, and network integrity. After replacement, clear codes and verify proper operation and communication.
- If fault persists, inspect gateway or other modules that route RSM messages and consult manufacturer network wiring diagrams.
Likely causes
- Corroded or wet connector at the rain sensor (common on windshield/housing)
- Damaged CAN wiring harness (chafing, pinch point near A-pillar)
- Loss of module supply or ground (blown fuse or open circuit)
- Faulty RSM hardware or internal CAN transceiver
Fault status
Status
Lost communication with Rain Sensing Module (no CAN messages received or intermittent communication). Related automatic wiper/rain sensing functions may be disabled.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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