U017C

Code

HYUNDAI U — Network/User

Lost Communication With “Restraints System Sensor M”

Brand: HYUNDAI

Type: U — Network/User

Views: UK: 11 EN: 17 RU: 11

AI status

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Page language: EN

Causes

Open or short in CAN bus wiring between Restraints Sensor M and gateway/RCM
Poor or corroded connector pins at Restraints Sensor M or intermediate junctions
Failed Restraints System Sensor M (internal electronics)
Failed restraint control module (RCM) or gateway module handling the bus
Low or intermittent battery/vehicle voltage affecting communications
Incorrect software/calibration or failed module programming

Symptoms

Airbag/restraints warning lamp illuminated
Possible disablement of some restraint functions (e.g., seat belt pretensioner or passenger airbag status)
Related U‑codes for other modules on same CAN bus
Loss of occupant detection or seatbelt sensor data (if sensor handles those)
Intermittent or permanent fault, depending on root cause

What to check

Retrieve full code set and freeze frame with a scan tool; note any additional U‑codes or related B/P codes
Check for recent events (repairs, seat removal, collisions) that could have disturbed wiring or connectors
Visually inspect connectors and harness at Restraints Sensor M, RCM/gateway and under-seat areas for damage, corrosion, or loose pins
Check vehicle battery voltage and charging system; ensure stable supply (12.6V+ at rest)
With key on (engine off), measure CAN bus idle voltages at the sensor connector: CAN_H and CAN_L
Check continuity between sensor connector and gateway/RCM for CAN_H, CAN_L, power and ground; inspect for shorts to chassis

Signal parameters

CAN bus idle voltages (typical): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (recessive)
Dominant state typical: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈2.0 V)
Bus termination resistance: ≈ 60 ohms (two 120 Ω terminators in parallel)
Typical high‑speed CAN bitrate used by restraints networks: commonly 500 kbps (model dependent)
Module power supply: battery nominal 12 V (verify exact vehicle values)

Diagnostic algorithm

Safety first: disable SRS system per manufacturer procedure (battery disconnect and wait period) before disconnecting restraint modules or connectors
Connect a professional scan tool and confirm U017C is present; record freeze frame and other related codes
Clear the code and attempt to reproduce; note whether code returns immediately or intermittently
Inspect physical condition of wiring and connectors at Restraints Sensor M, under the seat, and at the RCM/gateway for damage, corrosion, or loose pins
Verify battery voltage and main ground connections; recharge or repair charging system if voltage is low or unstable
With ignition ON (follow SRS safety precautions), backprobe sensor connector: check B+ and ground are present and measure CAN_H and CAN_L idle voltages
Measure resistance between CAN_H and CAN_L at the sensor connector (expect ≈60 Ω). If open or very high, trace missing termination or open circuit
Use a scope or CAN analyzer to observe CAN waveforms while scanning; look for noise, missing messages, or inability to enter dominant/recessive states
If wiring is open or shorted, repair harness or connector and re-test
If wiring and power/ground are good but no communication from sensor, replace or reprogram Restraints System Sensor M per manufacturer procedure
If replacement module does not fix communications, suspect RCM/gateway fault and pursue module-level diagnostics or replacement
After any repair, clear codes and perform full system scan and function test; verify no new codes and that restraints lamp behaves correctly

Likely causes

Corroded/loose connector at Restraints Sensor M
Broken/shorted CAN H or CAN L wires near seat or sensor location
Failed Restraints System Sensor M module
Missing/failed CAN termination or short to chassis
Low vehicle battery or poor ground at sensor/module

Fault status

⚠️ Status

Lost communication with Restraints System Sensor M. Check CAN bus wiring, connectors, power/ground, and module for faults. Follow SRS safety procedures before repairs.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours

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U017C — Lost Communication With “Restraints System Sensor M”