2013-2017 Audi A4, S4, A5, S5, Q5 & SQ5 Side Assist Sensor Failure and Replacement

Symptoms of a Failing Side Assist Sensor

When a Side Assist radar sensor fails, the entire system typically shuts down as a safety precaution. You will usually see a clear message on your instrument cluster display and notice the system is no longer functional.

• "Audi Side Assist: system fault" Warning: This is the most common and direct indicator of a hardware or communication problem within the system. The message will appear on the Driver Information System (DIS) screen between your gauges.
• "Audi side assist unavailable: Sensors blocked" Message: While this can be caused by actual obstructions like mud, snow, or ice, it can also indicate an internal sensor failure. If the message persists after the bumper has been thoroughly cleaned, it often points to a faulty module.
• Inoperative Mirror Lights: The yellow LED warning lights in your side mirrors will not light up when a car is in your blind spot. They may also fail their initial self-check flash when you start the car.
• System Grayed Out in MMI: In the vehicle's Multi Media Interface (MMI), the option to turn on or adjust the Side Assist system will be grayed out and inaccessible.
• Intermittent Operation: Before failing completely, the system might work sporadically, often cutting out in heavy rain or after a car wash. This is a strong sign of water beginning to penetrate the sensor's housing.

Known Issues, TSBs, and Recalls

The primary cause of failure for these sensors is their location, which exposes them to harsh conditions.

Common Causes of Failure

• Water Intrusion: This is the number one reason these modules fail. Over time, the plastic housing can develop hairline cracks, allowing moisture to seep in and corrode the internal circuit board. This corrosion is often visible as white or green powder on the electrical connector pins.
• Physical Damage: Even a minor impact to the rear bumper can crack the sensor's housing or break its mounting bracket, leading to failure or misalignment.
• Improper Bumper Repair: If the rear bumper is repainted, excessive paint thickness over the sensor area can block the radar signals and cause the system to malfunction.

Technical Service Bulletins (TSBs)

Audi issued TSB 96 13 60 2033943/1 for an issue where the "Audi side assist unavailable: Sensors blocked" message appears during specific driving conditions, like very slow stop-and-go traffic or long drives on empty roads with nothing for the radar to track. The bulletin notes this is a software sensitivity issue and advises against replacing hardware for this specific complaint, as a software update was planned to address it.

Recalls

As of early 2026, there are no specific NHTSA recalls for the Side Assist sensors on the 2013-2017 Audi A4, S4, A5, S5, Q5, or SQ5. While recalls exist for these models concerning other components like fuel pump flanges, they do not pertain to the blind spot monitoring system.

Buying a Used Collision Avoidance Sensor

A used OEM sensor is a great way to save a significant amount of money compared to a new dealer part. However, these are sensitive electronic modules, and careful inspection is key. A used OEM part that passes inspection is often a more reliable choice than a new, unproven aftermarket part.

1. Verify the Part Number: This is the most critical step. The part numbers are side-specific. While you should always match the number on your original part, the general rule for these Audis is:
   • Left (Driver) Side: 8T0907566B
   • Right (Passenger) Side: 8T0907568B
   Older revisions without the 'B' suffix may exist but the 'B' version is the most updated and preferred.
2. Inspect the Housing: Carefully examine the black plastic casing for any cracks, no matter how small. A cracked housing is how water gets in. Check that all mounting tabs are intact.
3. Check the Connector: Look inside the electrical connector port. The pins should be straight and clean. Any sign of green or white crusty residue is a deal-breaker, as it indicates terminal water damage.
4. Ask About the Source Vehicle: If possible, find out if the donor car had a front or side impact. A sensor from a car with a clean rear end is always a safer bet than one from a rear-end collision.

Replacement and Calibration Guide

Physically replacing the sensor is manageable for a DIYer, but completing the job requires professional tools. The process involves removing the rear bumper, swapping the module, and then having it professionally programmed and calibrated.

1. Bumper Removal

This is the most labor-intensive step. You will need to remove screws in the rear wheel wells, fasteners underneath the car, and bolts inside the trunk area to release the bumper cover. The exact procedure varies slightly between the A4/S4 sedans, A5/S5 coupes, and Q5/SQ5 SUVs, but the principle is the same.

2. Sensor Replacement

Once the bumper cover is off, you will see the radar modules bolted to brackets in each corner. Simply unplug the electrical connector and remove the bolts holding the old sensor. Install the new sensor, ensuring it is seated correctly on its bracket.

3. Component Protection Removal (Professional Step)

Audi vehicles use an anti-theft system called Component Protection (CP). When you install a used module, the car recognizes it's from a different vehicle and puts it in a locked state. The Side Assist system will not function until this lock is removed. This procedure can only be done by an Audi dealer or a specialized independent shop with an online subscription to Audi's factory tools (ODIS). A VCDS tool cannot remove Component Protection.

4. ADAS Calibration (Professional Step)

After Component Protection is removed, the sensor must be calibrated. This process aligns the radar, telling it exactly where it is positioned on the car so it can accurately detect other vehicles. This requires special calibration boards and diagnostic software. Driving without proper calibration can lead to the system not working or, worse, giving inaccurate warnings. This step is mandatory for the system to function correctly and safely.

Cost to Replace an Audi Side Assist Sensor

Costs can vary significantly based on whether you perform the physical labor yourself and the price of the part.

Frequently Asked Questions (FAQ)