A faulty restraints system sensor 'H' that has failed internally and stopped transmitting data.; Damaged or corroded wiring or connectors between the sensor and the restraints control module.; A blown fuse or poor ground connection supplying power to the sensor or its communication circuit.; A failed restraints control module that cannot receive or process the sensor's signal.; Communication bus faults such as a shorted or open data line affecting multiple modules.; Water intrusion or physical damage to the sensor or its harness from a collision or environmental exposure.

DTC codes / U01xx · Lost communication with a control module / U0177

U0177Lost Communication With 'Restraints System Sensor H'

Q: What does code U0177 mean?

Lost Communication With 'Restraints System Sensor H'. U0177 is a network communication fault indicating that a control module, typically the airbag or restraints control module, has lost the data signal from a specific restraints system sensor designated 'H'. The computer has detected that the expected periodic message from that sensor is missing on the vehicle's communication bus, which can disable part of the supplemental restraint system.

U0177 is a network communication fault indicating that a control module, typically the airbag or restraints control module, has lost the data signal from a specific restraints system sensor designated 'H'. The computer has detected that the expected periodic message from that sensor is missing on the vehicle's communication bus, which can disable part of the supplemental restraint system.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaLost communication with a control module

Symptoms you may notice

The airbag or supplemental restraint system (SRS) warning light is illuminated on the dashboard.
A chime or message may appear indicating a restraint system fault or service airbag soon.
The airbag system may be disabled, meaning airbags will not deploy in a collision.
Often no symptoms besides the warning light, with the vehicle driving normally.
Other unrelated warning lights may appear if the communication bus is shared with other modules.

Common causes, most likely first

A faulty restraints system sensor 'H' that has failed internally and stopped transmitting data.
Damaged or corroded wiring or connectors between the sensor and the restraints control module.
A blown fuse or poor ground connection supplying power to the sensor or its communication circuit.
A failed restraints control module that cannot receive or process the sensor's signal.
Communication bus faults such as a shorted or open data line affecting multiple modules.
Water intrusion or physical damage to the sensor or its harness from a collision or environmental exposure.

How to diagnose and fix it

Connect a scan tool and read all stored codes in every module to confirm U0177 and identify related communication faults.
Inspect the restraints system sensor 'H' and its wiring for visible damage, corrosion, or loose connectors.
Check the fuse and ground connections for the sensor circuit and the restraints control module.
Measure resistance and voltage on the communication bus at the sensor connector to verify signal integrity.
If the sensor is accessible, substitute a known-good sensor or perform a wiggle test on the harness while monitoring live data.
Repair or replace damaged wiring, connectors, or the sensor as indicated by test results.
Clear the codes and verify the repair by cycling the ignition and confirming the warning light stays off.

What most technicians overlook with U0177

A loose or corroded ground connection at the restraints control module can mimic a failed sensor and set U0177 without any sensor fault at all.
The sensor designated 'H' is often part of a daisy-chained bus, so a fault in an earlier sensor or connector can cause multiple sensor communication codes including U0177.
After a collision repair, U0177 frequently appears because the restraints system needs a calibration or the sensor was not reconnected properly during reassembly.
Some vehicles require a relearn or initialization procedure after replacing the restraints control module or sensor, and skipping it will leave U0177 stored even with good parts.
U0177 can be set by a low battery or charging system fault that causes momentary voltage drops on the communication bus, so always check battery health first.

Can I keep driving with U0177?

The vehicle is generally safe to drive because the fault affects the airbag system rather than engine or brakes, but the airbags may not deploy in a crash. Avoid any driving that could lead to a collision until the fault is repaired, and have the system diagnosed promptly.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.