Lost Communication With Restraints System Sensor H
The U0177 code means the vehicle's onboard diagnostic system has detected: Lost Communication With Restraints System Sensor H. This is a serious severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- moderate
- Estimated cost
- $50 - $600 (fuses, grounds, or wiring most often; module replacement only after the circuit tests good)
Network codes mean modules are not communicating. You need a scanner that reads all systems to find the problem.
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Common Symptoms
- Check Engine or related warning light on
- The Restraints System Sensor H's functions may be degraded or offline
- Often stored alongside other U-codes when a whole bus segment drops
- Symptoms can be intermittent - connector and wiring faults come and go with heat and vibration
Probable Causes (Ranked by Likelihood)
- The Restraints System Sensor H has lost power or ground (check its fuses first) High
- CAN bus wiring damage - chafed harness, corroded connector, water intrusion High
- Failed Restraints System Sensor H no longer transmitting Moderate
- Another faulted module loading down the bus Low
Frequently Asked Questions
What does U0177 mean?
U0177 means other modules stopped receiving messages from the Restraints System Sensor H on the vehicle network. It is a communication fault - the module may be fine but unreachable.
Can I keep driving with U0177?
Cautiously and briefly - a communication fault involving a safety-related module (Restraints System Sensor H) can degrade braking, stability, or restraint functions without much warning. Diagnose promptly.
Should I replace the module for U0177?
Not first. Most communication codes are power, ground, fuse, or wiring problems. Replace the module only after those test good - modules are expensive and often require programming.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
-
Scan ALL modules - the pattern of which modules report lost communication localizes the break.
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Check the fuses and grounds feeding the Restraints System Sensor H before suspecting the module itself.
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If many modules are unreachable, test the CAN bus: about 60 ohms across CAN High/Low (two 120-ohm terminators) with the battery disconnected.
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Wiggle-test connectors along the affected harness while watching for the module to drop on and off.
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Only after power, ground, and bus test good should the Restraints System Sensor H be suspected.
Sources 2
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
- Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition
Commonly Affected Vehicles
- All OBD-II vehicles - network (U) codes are standardized across makes
Related Codes
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