U0172: Lost Comms with Restraint Sensor C
Diagnostic trouble code U0172 indicates that the Restraint Control Module (RCM) has lost serial communication (typically over the CAN or LIN bus) with the 'Sensor C' of the restraint system. This sensor is usually a side impact sensor, rollover sensor, or occupant classification sensor, and its signal is critical for proper airbag and pretensioner deployment strategy.
1. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.
2. Most Common Causes
- Open circuit, short to ground/battery, or short between communication bus wires to Sensor C
- Damaged, corroded, or disconnected connector at Sensor C
- Internal failure of Sensor C (defective communication electronics)
- Data bus integrity issues (termination, interference, another node hanging the bus)
3. Symptoms You Will Notice
- Airbag warning light illuminated
- Supplemental Restraint System (SRS) fault message on dashboard
4. Step-by-Step Diagnosis
Scan for all stored codes and freeze frame data
Visually inspect Sensor C connector and wiring for damage, corrosion, or loose connection
Check communication bus wiring for opens, shorts, and proper termination resistance
Test Sensor C power and ground circuits
If wiring is okay, attempt to communicate with Sensor C using a scan tool; if no response, replace Sensor C
If problem persists, suspect RCM failure and test/replace RCM
5. Frequently Asked Questions
Is it safe to drive?▼
No, it is not safe to drive. This code indicates a critical communication loss that may prevent airbag deployment in a crash, increasing injury risk.
How much does it cost to fix?▼
Repair costs typically range from $150 to $600, depending on whether the issue is a wiring repair ($150-$300) or sensor replacement ($200-$600).