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Blind Spot Monitoring Malfunction on 2020 Mazda 3

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Christine P. · rep 0 · May 22, 4:50 AM · 1 replies · solved · Question

Vehicle: 2020 Mazda 3 Premium

My 2020 Mazda 3 Premium has an intermittent "Blind Spot Monitoring Malfunction" warning on the dash. It comes and goes, sometimes staying off for days, then popping up again. When it's active, the BSM system obviously doesn't work, which is a safety concern.

I've checked the sensors for dirt or obstructions, especially after washing the car, but they seem clean. It doesn't seem to be triggered by specific weather conditions either. Is this a common issue with these models?

It's really annoying and makes me nervous about changing lanes without that extra layer of safety. Any thoughts on what might be causing this intermittent error?

✓ Accepted solution

ClearTheCode Admin

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

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ClearTheCode admin answer:

An intermittent "Blind Spot Monitoring Malfunction" on your 2020 Mazda 3 Premium is a common concern and can be frustrating. The BSM system relies on radar sensors, typically located behind the rear bumper, and a control module to function correctly.

Here are the potential causes and steps to consider:

  1. Sensor Obstruction/Damage: While you've checked for dirt, even minor damage to the bumper cover in the sensor's vicinity, or a slight misalignment of the sensor itself, can cause issues. Sometimes, moisture ingress into the sensor unit can also lead to intermittent faults.
  2. Wiring or Connector Issues: Intermittent problems often point to a loose or corroded electrical connection. The wiring harness leading to the BSM sensors or the BSM control module could have a compromised connection. Vibrations from driving can cause these connections to temporarily lose contact.
  3. Software Glitch: Sometimes, the BSM module's software can experience a temporary glitch. A simple battery disconnect for 15-30 minutes (to reset modules) might temporarily clear it, but if it returns, it's likely a hardware or persistent software issue.
  4. Faulty BSM Sensor or Module: If the above checks yield nothing, one of the radar sensors or the BSM control module itself might be failing. Intermittent failure is often a precursor to complete failure.
  5. Diagnostic Trouble Codes (DTCs): A professional scan tool can read specific codes related to the BSM system. Look for codes like B2206 (BSM System Malfunction), U0159 (Lost Communication With BSM Control Module), or specific sensor codes that can pinpoint which sensor (left or right) is causing the issue.

When to See a Shop:

  • If the issue persists despite checking for external obstructions.
  • If you're unable to access or inspect the sensor wiring yourself.
  • If you want a definitive diagnosis, as specialized tools are needed to read BSM-specific codes and potentially recalibrate the sensors after inspection or replacement. A Mazda dealership or an advanced automotive electrical shop is recommended.
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