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2019 GLC 300 Blind Spot Assist Inoperative - No Sensors Blocked

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Mike T. · rep 0 · May 22, 4:16 AM · 1 replies · solved · Question

Vehicle: 2019 Mercedes-Benz GLC 300

My 2019 Mercedes-Benz GLC 300 (X253) is showing a 'Blind Spot Assist Inoperative' message on the dash, and the warning triangles in the mirrors aren't lighting up. I've checked the rear bumper, and there's no dirt, snow, or damage blocking the sensors. I've also tried restarting the car multiple times, but the message persists.

This started happening suddenly, and I haven't had any recent accidents or bodywork. Is there a common electrical issue that causes this? Could it be a sensor failure or something more complex with a control module? I'm hoping it's not an expensive fix.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:16 AM

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ClearTheCode admin answer:

The 'Blind Spot Assist Inoperative' message on your 2019 GLC 300 indicates a fault within the system responsible for monitoring your blind spots. Since you've confirmed no physical obstructions, the issue is likely electrical or sensor-related.

Common Causes:

  1. Faulty Radar Sensor: The Blind Spot Assist system relies on radar sensors located in the rear bumper. These sensors can fail due to internal defects, water intrusion, or minor impacts that aren't externally visible.
  2. Wiring Harness Damage: The wiring connecting the sensors to the control module can become damaged, leading to intermittent or complete signal loss.
  3. Control Module Malfunction: The Blind Spot Assist control module (often integrated with other driver assistance systems) can fail, preventing proper operation.
  4. Calibration Issue: After a minor bump or even sometimes spontaneously, the sensors might lose their calibration, requiring a dealer recalibration.

Relevant OBD-II Codes (Mercedes-specific):

  • U0155: Lost Communication With Blind Spot Monitor (BSM) Control Module.
  • B2200 series codes: Often relate to specific radar sensor faults (e.g., B2201 for left rear sensor, B2202 for right rear sensor).
  • C1XXX series codes: Can indicate issues with sensor data or calibration.

Troubleshooting Steps:

  1. Visual Inspection (Detailed): Carefully inspect the entire rear bumper area, especially where the sensors are located (usually behind the bumper cover on the corners), for any subtle signs of damage or loose connections.
  2. Check Fuses: Consult your owner's manual for the fuse associated with the Blind Spot Assist system and check if it's blown.

When to See a Shop:

Given the complexity of radar-based systems, it's highly recommended to take your 2019 GLC 300 to a Mercedes-Benz dealership or a specialized independent shop. They have the necessary diagnostic equipment (XENTRY/DAS) to read specific fault codes from the Blind Spot Assist control module. These codes will pinpoint whether it's a sensor failure, wiring issue, or a module problem. Furthermore, if a sensor is replaced, it will require precise calibration using specialized tools, which only a qualified technician can perform correctly to ensure the system functions safely and accurately.

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