What it means
A control module is not receiving expected messages from Restraints System Sensor L. The code indicates a communication fault; the sensor's specific role depends on the vehicle.
At a glance
- Usually lights the warning light of the system that lost communication
How it works
Restraints System Sensor L is a vehicle-specific input to the restraint system and communicates its data over the vehicle network. A control module stores U017B when Sensor L messages are absent for the required interval, which may result from a sensor power or wiring fault, incorrect gateway routing, or a CAN termination problem.
Common causes
Most likely first.
- Sensor unpowered or wiring broken
- Gateway module routing CAN messages incorrectly
- CAN terminating resistor (120 Ω) drifted out of spec
Symptoms
- Airbag or restraint-system warning
- Restraint functions associated with the sensor may be impaired
- Other communication codes
How to diagnose it
- Scan all modules and examine freeze-frame data to find whether U017B occurred alongside other communication faults or low voltage.
- Identify Sensor L from vehicle service information and inspect its connector and wiring for corrosion, damage, loose pins, or a disconnected connection.
- Check Sensor L power and ground against the manufacturer's specification.
- Review gateway and network codes to see whether the fault is limited to Sensor L or affects other modules too.
- Test the CAN wiring and termination using the manufacturer's procedure; do not assume the network uses one universal termination reading.
- If the supply, gateway, and network checks pass, test Sensor L according to the manufacturer's restraint-system diagnostic procedure.
Common fixes
- Repair the Sensor L power or ground connection if it is faulty.
- Clean, secure, or repair the sensor connector and harness.
- Correct a confirmed CAN wiring or gateway routing fault.
- Replace Sensor L if the prescribed tests show it has failed.
Can I keep driving?
A restraint function associated with Sensor L may be unavailable, so have the fault diagnosed promptly and drive cautiously. Avoid working on restraint wiring unless the vehicle’s safety procedure is being followed.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.