2017-2020 Acura MDX Blind Spot System: Sensor & Bracket Failure Guide
Diagnose common 'Blind Spot Info System Problem' warnings, understand why sensor alignment is critical, and learn what to inspect before buying a used radar unit for your MDX.
- The most common failure is a "Blind Spot Info System Problem" warning, often caused by a faulty rear radar sensor or misalignment after even a minor rear bumper impact.
- Sensor replacement requires removing the rear bumper and a mandatory electronic aiming (calibration) procedure using special dealer-level tools and targets. This is not a simple DIY job.
- The mounting brackets (PNs 36934-TZ5-A11 and 36939-TZ5-A11) are critical for alignment; a bent bracket will prevent the system from working even with a good sensor.
- When buying a used sensor, inspect the case for cracks and ensure the connector pins are clean and straight to avoid purchasing a water-damaged or non-functional unit.
Symptoms of a Failing Blind Spot System
When the Blind Spot Information (BSI) or related collision avoidance systems in your 2017-2020 Acura MDX begin to fail, your vehicle will typically alert you with specific messages on the Multi-Information Display (MID) located in your instrument cluster.
- "Blind Spot Info System Problem" Message: This is the most direct indication of a fault within the BSI system. It means the control unit has detected a problem with one or both of the rear radar sensors, their wiring, or their calibration.
- "Collision Mitigation System Problem" Message: Because the blind spot sensors provide data to other safety systems, a fault in one can trigger warnings for others. You may see this message in conjunction with the BSI warning.
- Flashing BSI Indicators: In some cases, the amber warning lights on the side pillars may flash continuously, even when no vehicle is present, indicating a system malfunction.
- System Works Intermittently: The system may work correctly sometimes but fail at others. This can be a sign of a loose connection, water intrusion in a connector, or an early-stage sensor failure.
- System Inoperative: The BSI system may be completely non-functional, providing no warnings at all. You might notice that the feature cannot be turned on through the vehicle's settings menu.
Pro Tip: The BSI system is designed to be inactive at speeds below 20 mph and can be temporarily affected by heavy rain, snow, or fog. If the warning appears only in these conditions and disappears afterward, it may be normal operation. However, if the warning persists in clear weather, it indicates a genuine fault.
Known Issues for the 2017-2020 Acura MDX
While generally reliable, the BSI system on the third-generation MDX has a few known vulnerabilities.
- Sensitivity to Rear Impacts: Even a minor bump to the rear bumper can knock a radar sensor or its mounting bracket out of alignment. This can happen without any visible damage to the bumper cover itself. If the system fails immediately after a minor rear-end collision, misalignment is the most likely cause.
- Software Glitches: Some issues with Acura's driver-assist systems can be caused by software logic. A Technical Service Bulletin (TSB) for the 2017 MDX notes that incorrect detection logic in the multipurpose camera software can cause various warning lights, including for the Collision Mitigation Braking System (CMBS), to appear. A dealership may be able to resolve these issues with a software update. 🎬 Watch: How to resolve multiple dashboard warning lights
- Water Intrusion: Though sealed, the radar units or their electrical connectors can be susceptible to water damage over time, leading to corrosion and failure. This is more common in regions with heavy rainfall or harsh winters.
Warning: A faulty Blind Spot Information system also disables the Rear Cross Traffic Monitor, which uses the same radar sensors to warn you of approaching vehicles when you are backing out of a parking space.
Buying a Used 2017-2020 MDX Blind Spot Radar Unit
Given the high cost of new OEM radar units, a used sensor is an excellent value. However, these are sensitive electronic components, and careful inspection is key.
Why Choose a Used OEM Sensor?
Original Equipment Manufacturer (OEM) sensors are designed specifically for your MDX's software and mounting points. They are far more likely to function and calibrate correctly than aftermarket alternatives. Aftermarket sensors can have compatibility issues that may prevent the mandatory calibration procedure from completing successfully.
Physical Inspection Checklist
Before purchasing a used radar unit, perform a thorough physical inspection:
- Check the Housing: Look for any cracks, chips, or signs of stress on the black plastic casing. A compromised case can allow water to enter and destroy the internal electronics.
- Inspect the Connector: The electrical connector pins should be clean, straight, and free of any green or white corrosion. Damaged or corroded pins will prevent the sensor from communicating with the vehicle.
- Verify Mounting Points: Ensure all mounting tabs are intact and not cracked or broken. A sensor that cannot be securely fastened will be impossible to align.
- Ask About the Donor Vehicle: If possible, find out if the donor vehicle had a rear-end collision. A sensor from a vehicle with heavy rear damage is a risky purchase, as it may have internal damage or be misaligned.
The Importance of the Mounting Brackets
The specific parts listed in our database—36934-TZ5-A11 (Right) and 36939-TZ5-A11 (Left)—are the brackets, or sensor protectors, that hold the radar units. These are not just simple pieces of plastic; they are engineered to hold the sensor at a very specific angle. A bent, cracked, or incorrect bracket will make proper alignment impossible, rendering even a brand-new sensor useless. If you are replacing a damaged bracket, always use a new or verified-straight used OEM part.
Replacement & Calibration: Not a Simple DIY Job
Physically replacing the sensor involves removing the rear bumper cover, which is a moderately difficult task. However, the critical step that follows makes this a challenging job for most DIY mechanics.
Mandatory Calibration Required: After a blind spot radar sensor is replaced or even just disturbed, a procedure called BSI Radar Static Aiming must be performed. This process requires an Acura-compatible diagnostic scan tool and special physical targets (reflectors) placed at precise distances and angles behind the vehicle. Without this calibration, the system will not work correctly and will continue to display a fault message. This procedure is typically performed by an Acura dealership or a well-equipped independent auto body or repair shop.
🎬 See how professional ADAS calibration is performedCost Comparison for MDX Blind Spot System Repair
| Part or Service | Estimated Cost |
|---|---|
| New OEM Radar Sensor (e.g., 36931-TZ5-A21) | $750 - $1,150 |
| New OEM Mounting Bracket (e.g., 36934-TZ5-A11) | $40 - $70 |
| Used OEM Radar Sensor | $150 - $400 |
| Shop Labor (Replacement) | $125 - $200 |
| Shop Labor (Calibration) | $150 - $300 |
OEM Part Numbers
| Part Name | Side | Part Number(s) |
|---|---|---|
| Radar Sensor Unit | Right (Passenger) | 36930-TZ5-A21, 36931-TZ5-A21 |
| Radar Sensor Unit | Left (Driver) | 36935-TZ5-A21 |
| Mounting Bracket / Cover | Right (Passenger) | 36934-TZ5-A11 |
| Mounting Bracket / Cover | Left (Driver) | 36939-TZ5-A11, 36939-TZ5-A31 |
Frequently Asked Questions (FAQ)
What does the "Blind Spot Info System Problem" warning mean?
This message indicates that the vehicle's main computer has detected a fault in the blind spot monitoring system. Common causes include a failed radar sensor, damaged wiring, a misaligned sensor due to a bumper impact, or a software issue. The system will be disabled until the fault is corrected.
Can I just replace the mounting bracket if it's broken?
Yes, you can replace just the bracket. However, any time the sensor is unbolted and reinstalled, even on a new bracket, the system's alignment is disturbed. You must have the BSI radar aiming procedure performed afterward to ensure it functions correctly.
Do I have to get the sensor calibrated at an Acura dealer?
While an Acura dealership is the most common place for calibration, many independent auto body shops and repair facilities that specialize in Advanced Driver-Assistance Systems (ADAS) also have the necessary equipment (scan tools and targets) to perform the aiming procedure. It is not a procedure that can be done without this specialized equipment.
🎬 Watch: Honda and Acura blind spot calibration demoWhy did my blind spot sensor stop working after a minor accident with no visible damage?
The radar sensors are mounted on precise brackets just behind the bumper cover. Even a low-speed impact can bend the bracket or shift the sensor's position slightly. This change in angle is enough to prevent the sensor from reading the road correctly, causing the system to shut down and display a warning message.
Helpful Videos
Technical Specifications
OEM Part Numbers: 36934-TZ5-A11 36934TZ5 36939-TZ5-A11 36939TZ5 36930-TZ5-A21 36931-TZ5-A21 36935-TZ5-A21 36939-TZ5-A31
The system consists of two radar sensor units mounted behind the left and right corners of the rear bumper. Operates at speeds above 20 mph.
We Have This Part in Stock
The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- Acura MDX:
- 🎬 Helpful Videos
- 🛍️ Shop This Part
- Symptoms of a Failing Blind Spot System
- Known Issues for the 2017-2020 Acura MDX
- Buying a Used 2017-2020 MDX Blind Spot Radar Unit
- Why Choose a Used OEM Sensor?
- Physical Inspection Checklist
- The Importance of the Mounting Brackets
- Replacement & Calibration: Not a Simple DIY Job
- Cost Comparison for MDX Blind Spot System Repair
- OEM Part Numbers
- Frequently Asked Questions (FAQ)
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