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Blind Spot Monitor Malfunction on 2018 Mazda3

0

Jennifer H. · rep 0 · May 22, 4:50 AM · 1 replies · solved · Question

Vehicle: 2018 Mazda3 Touring

I'm having an issue with my 2018 Mazda3 Touring. The Blind Spot Monitoring (BSM) system and Rear Cross Traffic Alert (RCTA) have stopped working. I get a warning light on the dash, and sometimes it says "BSM Malfunction" on the infotainment screen.

It seems to happen randomly, but more often when it's raining or after a car wash. I've tried cleaning the sensors on the rear bumper, ensuring there's no dirt or debris, but no luck. It's a safety feature I rely on, so I'm keen to get it fixed.

Has anyone else experienced this with their Mazda3? Is there a common fix or something I should check before heading to the dealership?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:50 AM

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ClearTheCode admin answer:

Blind Spot Monitoring (BSM) and Rear Cross Traffic Alert (RCTA) malfunctions are often related to the radar sensors located in the rear bumper. The fact that it happens more frequently in wet conditions is a significant clue.

Here are the common causes and diagnostic steps:

  1. Sensor Obstruction/Damage: While you've cleaned them, even minor damage to the bumper cover over the sensor area, or internal damage to the sensor itself, can cause issues. Water ingress can also short out or interfere with the sensor's operation.
  2. Wiring Harness Issues: The wiring connecting the BSM sensors to the control module can become corroded, damaged, or have a loose connection, especially in areas exposed to road spray and moisture. This is a strong possibility given your symptoms.
  3. BSM Control Module Failure: Less common, but the BSM control module itself (often located in the trunk area) could be faulty. Water intrusion into the trunk can sometimes affect these modules.
  4. Diagnostic Trouble Codes (DTCs): A scan tool will likely reveal specific codes related to the BSM system. Common codes include:
    • U0159: Lost Communication With BSM Control Module.
    • B2220: BSM Sensor Malfunction (Left or Right).
    • C1A60: BSM Sensor Internal Fault.
    • U0420: Invalid Data Received From BSM Control Module.

When to see a shop:

  • If cleaning the sensors doesn't resolve the issue.
  • If you suspect wiring damage or corrosion, as this requires careful inspection and repair.
  • If a diagnostic scan reveals specific BSM-related DTCs, which will help pinpoint the exact faulty component.
  • If the issue persists, as BSM systems are complex and often require specialized diagnostic tools for accurate troubleshooting and calibration after repair. A Mazda dealership or a reputable independent shop with Mazda diagnostic capabilities would be your best bet.
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