U017B: Lost Comms with Left Restraint Sensor
Diagnostic trouble code U017B indicates that the Restraint Control Module (RCM, also known as ORC or ACM) has lost serial communication with the left-side restraint sensor, typically a side-impact satellite sensor, door pressure sensor, or occupant classification sensor designated as 'L' by the manufacturer. Communication occurs over a dedicated bus such as PSI5, private CAN, or LIN. The code sets when the RCM fails to receive valid status messages (including alive/rolling counter and CRC) from that sensor within a calibrated time window.
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, or short to battery in the communication bus or power supply to the left restraint sensor
- Damaged, loose, corroded, or pushed-back terminals in the left sensor connector
- Internal failure of the left restraint sensor (satellite, pressure, or occupant classification)
- Internal failure of the Restraint Control Module (RCM)
- Low battery voltage or voltage spikes disrupting bus communication
- Incorrect sensor installation or wrong sensor used after collision repair
3. Symptoms You Will Notice
- Airbag warning light illuminated
- Supplemental Restraint System (SRS) fault message on the instrument cluster
4. Step-by-Step Diagnosis
Scan the RCM for all stored codes and freeze frame data
Visually inspect the left restraint sensor connector and wiring for damage, corrosion, or loose pins
Measure voltage and ground at the sensor connector with the ignition on
Check communication bus signals (e.g., PSI5, LIN) with an oscilloscope for proper waveform and integrity
If wiring and power are okay, substitute the left sensor with a known-good unit and recheck communication
If the code persists, test the RCM by swapping or reflashing as per manufacturer procedures
5. Frequently Asked Questions
Is it safe to drive?▼
No, this is a critical fault. The airbag system may not deploy properly in a crash, increasing the risk of injury. Have the vehicle towed to a repair facility.
How much does it cost to fix?▼
Typical repair costs range from $150 to $600, depending on the cause. A simple connector repair may be under $200, while replacing a sensor or RCM can exceed $500.