Code
U0172
HYUNDAI
U — Network/User
Lost Communication With “Restraints System Sensor C”
Views:
UK: 11
EN: 21
RU: 19
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring between the restraints sensor and network gateway/ECU
- Corroded, loose or damaged connector at the sensor or module
- Failed restraints system sensor/module (internal electronics)
- Faulty CAN/LIN transceiver in gateway or sensor module
- Blown fuse or loss of power/ground to the sensor/module
- Network bus termination or wiring fault (extra resistance, short to battery/ground)
Symptoms
- SRS/airbag warning lamp illuminated or flickering
- Related restraints functions (seatbelt pretensioner, occupant classification) may be disabled or flagged
- Possible other network communication errors or multiple U0xxx codes
- Vehicle may log intermittent or permanent U0172 depending on fault permanence
What to check
- Read all stored DTCs and freeze-frame data with a diagnostic scanner; note related U or B codes
- Confirm whether the restraints sensor module appears on the network (module list/IDs) using a capable scan tool
- Visually inspect connectors and wiring at the restraints sensor C, associated junctions, ground points and related modules
- Check SRS-related fuses and main battery voltage with ignition ON
- Perform wiggle tests while monitoring communication to reproduce an intermittent fault
- Inspect for water intrusion, corrosion, or physical damage at harness runs and connector plugs
Signal parameters
- CAN bus idle voltages (typical): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V; dominant bit shows CAN_H ≈ 3.5 V and CAN_L ≈ 1.5 V (differential ≈ 2 V)
- Bus termination resistance (CAN_H to CAN_L) ≈ 60 Ω (two 120 Ω terminators in parallel)
- Sensor/module supply voltage with ignition ON ≈ 9–16 V (nominal ~12–14 V)
- Ground continuity: near 0 Ω between sensor ground pin and chassis ground
- Expected message: periodic restraints sensor message ID present on bus at steady intervals — no frames from Sensor C indicates lost comms
Diagnostic algorithm
- Connect a factory-capable or professional scan tool and confirm U0172 plus any related codes; record freeze-frame and live data
- Verify battery voltage (engine OFF and ON) and inspect/replace any blown SRS-related fuses
- Using wiring diagrams, identify the sensor C connector, module location and network routing
- Visually inspect and repair any damaged wiring, pins, or connectors; clean and reseat connectors
- Measure power and ground at the sensor connector with ignition ON; repair any open/low readings
- Measure CAN_H and CAN_L at the sensor connector; verify termination resistance (~60 Ω) and proper idle voltages
- Check for presence of sensor C messages on the bus with a scope/logic analyzer or scan tool; if messages absent, trace/back-probe toward gateway to find where frames stop
- Perform continuity and short-to-power/ground checks between sensor pins and ECU/gateway pins as per wiring diagram
- If wiring and power/ground are good and the bus communication is present at the harness but not at the sensor, replace the restraints sensor C module
- After repairs, clear codes, cycle ignition and verify codes do not return; perform SRS system normality check per manufacturer procedures
- Follow all SRS safety precautions and service manual steps — if unsure, refer to qualified technician or dealer due to safety-critical system
Likely causes
- Disconnected or poorly seated sensor connector under/near seat or in B-pillar
- Damaged CAN/LIN wires from chafing or recent service/wiring repair
- Failed sensor/module or failed CAN transceiver in the sensor
- Blown SRS-related fuse or poor ground at sensor module
Fault status
Status
U0172 — Lost Communication With “Restraints System Sensor C”: control module is not responding or no valid network messages received from the restraints sensor C.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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