What it means
The reporting module has lost communication with Restraints System Sensor H. It sets this code when expected sensor messages are not received for a specified time.
How it works
Restraints System Sensor H is a vehicle-specific sensor that sends data to the restraint control system over the vehicle network. The reporting module stores U0177 when it stops receiving Sensor H messages for the required time, which can happen if the sensor loses power or ground, its wiring or the network is faulty, or the sensor fails.
Common causes
Most likely first.
- Sensor H power or ground fault
- Damaged or corroded sensor wiring or connectors
- CAN bus fault
- Restraints sensor H failure
- Low battery voltage
Symptoms
- Airbag warning light
- Restraint system warning message
- Airbags or pretensioners may be unavailable
How to diagnose it
- Scan all modules for codes and review freeze-frame data to see whether U0177 appeared with low battery voltage or other network faults.
- Check battery condition and charging-system operation, since low system voltage can interrupt Sensor H communication.
- Use vehicle service information to locate Sensor H, then inspect its connector and wiring for corrosion, damage, loose pins, or signs of water entry.
- Check Sensor H power and ground at its connector against the manufacturer's specification.
- Test the relevant CAN wiring for opens, shorts, or poor connections using the manufacturer's procedure.
- If power, ground, and network wiring are sound, follow the manufacturer’s restraint-system tests to determine whether Sensor H has failed.
Common fixes
- Restore battery or charging-system voltage if it is low.
- Repair damaged wiring or clean and secure Sensor H connections.
- Repair a confirmed CAN network wiring fault.
- Replace Sensor H if testing confirms it has failed.
Can I keep driving?
An airbag or pretensioner function may be unavailable while this fault is present, so have the restraint system checked promptly and drive cautiously. Do not probe or handle restraint-system connectors unless you are following the vehicle’s specified safety procedure.
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.