Code
U0171
Generic
U — Network/User
Lost Communication With Restraints System Sensor B
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring between Sensor B and its control module
- Corroded, loose or damaged connector at the sensor or module
- Failed restraints sensor (Sensor B)
- Failed restraints control module or gateway module
- Loss of power or ground to the sensor (blown fuse, bad ground)
- Faulty vehicle data bus (CAN or LIN) or missing termination
Symptoms
- Airbag/SRS warning lamp illuminated
- Seatbelt reminder or restraint system warnings for the affected seat
- Diagnostic trouble codes related to restraints and communication bus present
- Some restraints features (airbag deployment, seatbelt pre-tensioner) may be disabled for that circuit
- Intermittent or persistent loss of functionality for affected restraint sensor
What to check
- Connect a capable scan tool and read stored and pending codes, noting freeze frame and occurrence counts
- Check for other communication codes (other U-codes) that indicate a bus problem
- Visually inspect wiring and connectors for Sensor B, the restraints control module, and any gateway modules
- Verify sensor supply voltage and ground with key ON
- Backprobe the sensor connector and wiggle harness while monitoring for changes
- Check fuses and fusible links related to the restraints system
Signal parameters
- Sensor supply voltage: approx. battery voltage (key ON) ~9–14 V (verify with wiring diagram for exact value)
- Sensor ground: low resistance to chassis ground (
- CAN bus idle voltages: CAN_H ≈ 2.5–3.5 V, CAN_L ≈ 1.5–2.5 V (both ~2.5 V recessive) and observable CAN frames when active
- LIN bus idle: pulled high to battery voltage via resistor; active low pulses toward 0 V (if sensor uses LIN)
- If sensor uses a switched signal: expected low/high logic levels per manufacturer (verify wiring diagram)
Diagnostic algorithm
- Verify the code with a scan tool and note freeze-frame data and frequency. Check for related U-codes.
- Inspect connectors and harness for Sensor B and the restraints module for corrosion, damage, water ingress or repair splices.
- Verify power and ground at Sensor B with key ON. Replace blown fuses or repair grounds as required.
- Backprobe the signal and power wires at the sensor. Monitor voltages while operating the circuit or while a technician wiggles the harness; look for intermittent connection.
- Check the vehicle data bus for activity: use a scope or CAN/LIN tester to confirm proper idle voltages and valid message traffic. Compare to a known-good reference if available.
- If bus is inactive or shows faults, trace bus wiring, check continuity between modules, and verify termination resistors (typically ~60 Ω across CAN_H and CAN_L).
- If wiring and bus are good, substitute or bench-test Sensor B if an approved procedure exists, or replace the sensor and re-test.
- If sensor replacement does not restore communication, consider faults in the restraints control module or gateway module; consult wiring diagrams and module addresses, then test or replace module as directed by manufacturer procedures.
- After repairs, clear codes, perform any required Restraints or occupant classification relearn procedures, and verify that the code does not return during normal use and that the SRS lamp is extinguished.
Likely causes
- Broken or intermittent wiring harness to Sensor B
- Corroded/loose connector at the sensor or module
- Sensor B internal failure
- Power/ground supply fault to sensor (fuse, splice, ground)
- CAN/LIN bus fault (short, open, missing termination) preventing module communication
Fault status
Status
Lost Communication With Restraints System Sensor B — restraints sensor 'B' not responding or missing valid messages on the vehicle data bus.
Repair difficulty: Medium
Diagnostic time: 0.5-3.0 hours
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Code
U0171
HYUNDAI
U — Network/User
Lost Communication With “Restraints System Sensor B”
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring between Sensor B and its control module
- Corroded, loose or damaged connector at the sensor or module
- Failed restraints sensor (Sensor B)
- Failed restraints control module or gateway module
- Loss of power or ground to the sensor (blown fuse, bad ground)
- Faulty vehicle data bus (CAN or LIN) or missing termination
Symptoms
- Airbag/SRS warning lamp illuminated
- Seatbelt reminder or restraint system warnings for the affected seat
- Diagnostic trouble codes related to restraints and communication bus present
- Some restraints features (airbag deployment, seatbelt pre-tensioner) may be disabled for that circuit
- Intermittent or persistent loss of functionality for affected restraint sensor
What to check
- Connect a capable scan tool and read stored and pending codes, noting freeze frame and occurrence counts
- Check for other communication codes (other U-codes) that indicate a bus problem
- Visually inspect wiring and connectors for Sensor B, the restraints control module, and any gateway modules
- Verify sensor supply voltage and ground with key ON
- Backprobe the sensor connector and wiggle harness while monitoring for changes
- Check fuses and fusible links related to the restraints system
Signal parameters
- Sensor supply voltage: approx. battery voltage (key ON) ~9–14 V (verify with wiring diagram for exact value)
- Sensor ground: low resistance to chassis ground (
- CAN bus idle voltages: CAN_H ≈ 2.5–3.5 V, CAN_L ≈ 1.5–2.5 V (both ~2.5 V recessive) and observable CAN frames when active
- LIN bus idle: pulled high to battery voltage via resistor; active low pulses toward 0 V (if sensor uses LIN)
- If sensor uses a switched signal: expected low/high logic levels per manufacturer (verify wiring diagram)
Diagnostic algorithm
- Verify the code with a scan tool and note freeze-frame data and frequency. Check for related U-codes.
- Inspect connectors and harness for Sensor B and the restraints module for corrosion, damage, water ingress or repair splices.
- Verify power and ground at Sensor B with key ON. Replace blown fuses or repair grounds as required.
- Backprobe the signal and power wires at the sensor. Monitor voltages while operating the circuit or while a technician wiggles the harness; look for intermittent connection.
- Check the vehicle data bus for activity: use a scope or CAN/LIN tester to confirm proper idle voltages and valid message traffic. Compare to a known-good reference if available.
- If bus is inactive or shows faults, trace bus wiring, check continuity between modules, and verify termination resistors (typically ~60 Ω across CAN_H and CAN_L).
- If wiring and bus are good, substitute or bench-test Sensor B if an approved procedure exists, or replace the sensor and re-test.
- If sensor replacement does not restore communication, consider faults in the restraints control module or gateway module; consult wiring diagrams and module addresses, then test or replace module as directed by manufacturer procedures.
- After repairs, clear codes, perform any required Restraints or occupant classification relearn procedures, and verify that the code does not return during normal use and that the SRS lamp is extinguished.
Likely causes
- Broken or intermittent wiring harness to Sensor B
- Corroded/loose connector at the sensor or module
- Sensor B internal failure
- Power/ground supply fault to sensor (fuse, splice, ground)
- CAN/LIN bus fault (short, open, missing termination) preventing module communication
Fault status
Status
Lost Communication With Restraints System Sensor B — restraints sensor 'B' not responding or missing valid messages on the vehicle data bus.
Repair difficulty: Medium
Diagnostic time: 0.5-3.0 hours
Similar codes
Repair manuals
Manual library for HYUNDAI
371
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