Radar Sensor Dirty Mercedes: C163691, Location & Real Fix

Initial Assessment

The owner had installed an AMG-style front bumper for cosmetic reasons. The warning appeared immediately after the modification — a clear sign that the radar sensor’s physical position had been compromised during the bumper swap. The sensor was not dirty and cleaning had no effect.

Workshop inspection: CLA W118 with AMG front bumper fitted. With the bonnet open, the front grille area shows the circular mounting ring where the radar sensor sits. Visual inspection from above was inconclusive — bumper removal was required to access the sensor bracket and confirm misalignment.

XENTRY Diagnostic Results

XENTRY scan — ABA control unit faults: C162C62: wheel speed values implausible, C174AFA & C174AFB: ABA calibration malfunction (Current and Stored), C111FB: radar sensor 1 blocked by dirt or foreign object (Stored), U0418FE: implausible data from traction system. The combination of C174AFA/AFB as current+stored alongside C111FB confirmed active calibration failure — not a transient dirt blockage.

Root Cause & Repair

With the bumper removed, the technician found the radar sensor module (A108) was not seated in its bracket at the correct angle. The AMG bumper uses a slightly different bracket orientation than the standard CLA bumper — the body shop had not adjusted for this, leaving the radar beam deflecting incorrectly.

Radar sensor (A108) removed: With the bumper off, the sensor was extracted from its bracket. The sensor face shows yellowish contamination — wax or adhesive residue from the bumper installation process. This was compounding the misalignment issue: both the physical angle and the sensor face contamination were contributing to the fault. Both were corrected before calibration.

The sensor bracket was repositioned to OEM specification for the AMG bumper configuration. The sensor face was cleaned. The system was then recalibrated using XENTRY ADAS calibration targets — positioning the target board at the factory-specified distance and height in front of the vehicle.

Freeze Frame Data — What the Scan Revealed

A full system scan with the Autel diagnostic tool confirmed fault code C111FB: Radar sensor 1 is blocked by dirt or by a foreign object — stored in the radar control unit. Crucially, the freeze frame data captured the exact conditions at the moment of fault:

Freeze frame data — environmental parameters: C111FB stored with: accelerator position below 25% (normal cruise), outside temperature 10–50°C range, battery voltage 14–15V (charging system healthy). These readings confirm the fault was not caused by low voltage or driver behaviour — purely environmental radar blockage.

Freeze frame data — vehicle conditions: Vehicle speed 80–130 km/h (motorway), ignition ON, drivetrain READY TO DRIVE, windshield washer status: Fast wipe. The fast wiper status directly correlates with the driver’s report of heavy rain — confirming the radar blockage was caused by rain/spray, not a hardware fault. This data is forensically valuable for accident investigation or warranty claims.

Findings & Key Insight

The freeze frame data perfectly matched the driver’s account — high speed, active wipers, heavy rain. No hardware fault was found. The sensor housing seal was inspected and found intact. The bumper area was cleaned and dried. All fault codes were cleared.

The system operated normally on the post-repair test drive. No warnings reappeared.

Diagnostic Scan Results

Autel scan — ABA (Front Radar Sensor) module: B220662: current VIN incorrect or not present — signal comparison faulty (Active and Stored — Event codes), C163691: calibration of front radar sensor malfunction — parameter outside permissible range (Active and Stored), B182700: coding of control unit incomplete (Active and Stored — Event codes). All three codes together are the definitive signature of a radar sensor replacement that was not electronically commissioned.

These three fault codes together tell a clear story: a new sensor was physically installed but the three mandatory electronic steps — VIN programming, control unit coding, and radar calibration — were not performed. The CAN Bus can see the sensor but cannot trust its data.

Three-Step Repair Procedure

1. 1VIN Programming: The new radar sensor was programmed with the vehicle’s VIN using the Autel diagnostic system. This registers the sensor on the CAN network and allows the ABA module to recognise it as the correct unit for this vehicle. Without this step, B220662 remains active.
2. 2Control Unit Coding: The radar control module was coded to synchronise with the Active Brake Assist, ESP, and Pre-Safe systems. This establishes the data communication protocols and re-links the radar to the powertrain CAN Bus. Without this step, B182700 remains active.
3. 3Radar Calibration: A calibration target board was positioned at the factory-specified distance and height in front of the vehicle. The calibration procedure via XENTRY/Autel aligned the radar beam angle within acceptable tolerances. Without this step, C163691 remains active.

New radar sensor (A108) — Bosch OEM unit: The replacement Bosch sensor correctly fitted for this vehicle. The dashboard warning visible in the background confirms the ADAS fault was still active at this point — physical installation alone is not sufficient. VIN programming, coding, and calibration must follow before the warning clears. Note: this is an OEM Bosch unit — aftermarket radar sensors often do not support the full VIN coding procedure required by Mercedes XENTRY.

Outcome

After all three steps were completed: B220662, C163691, and B182700 cleared successfully. Radar passed functional testing under static and dynamic conditions. Road test confirmed Active Brake Assist, Collision Prevention Assist Plus, and Adaptive Cruise Control all operating normally.