Door mirror with the amber blind spot warning triangle glowing in the glass

Mercedes Blind Spot Assist Fault: What It Means and How to Fix It

'Blind Spot Assist inoperative' on the dash of your A-Class, C-Class, GLC or E-Class, the triangle in the mirror glass staying dark, or warnings for cars that aren't there? The two radars behind the rear bumper corners feed Blind Spot Assist, and Active Lane Change Assist often drops with it because it reads the same pair. Rear bumper work is the usual trigger. Here's what's happening, the free checks worth doing first, and what recalibration costs, from £162 inc VAT.

Please note

Before driving with a warning

Do not rely on the affected assistance feature. Follow the warning instructions in your handbook. If you are unsure about the vehicle's condition or whether to drive, get advice from a qualified repairer before travelling.

What's actually triggering Blind Spot Assist on your Mercedes

Use the repair history and exact warning to describe the problem. These situations can affect the next step; none is a diagnosis from the dashboard alone.

Removal, repair, repainting or refitting can trigger model-specific checks or calibration. It does not prove every nearby sensor moved. Include the repair record, any affected brackets and whether sensors were removed or replaced. A tidy outer panel does not establish that the installation behind it is sound.

The full repair history matters, including damage that was repaired before you acquired the car. A warning after a collision does not prove calibration alone will fix it. Mounting, wiring, compatible parts and completed installation may need checking first. Send existing reports rather than deliberately testing the assistance system.

Electrical or configuration problems can affect assistance functions without a sensor needing aiming. Include the fitted equipment and wiring work, when the warning began and any diagnostic findings. A fault appearing after the work is relevant history, not a diagnosis. Calibration cannot repair wiring or complete every configuration task.

One sensor can support more than one function, while an assistance system can use information from several components. Several warnings therefore do not establish one fault or a particular number of calibrations. Include every message and the complete repair history so the findings can be considered together.

Where and when an event happens can help an investigation. A repeat location does not prove the system is healthy, and a random pattern does not prove an aiming fault. Record the circumstances and any warnings without deliberately reproducing unexpected braking or steering behaviour.

Dirt, snow, ice or an obstruction can limit some sensors. Follow the cleaning instructions in the vehicle handbook while safely parked. Do not remove trim or adjust a sensor. A message that clears does not cancel calibration required after a repair, and a message that persists does not prove misalignment.

Calibration cannot repair a cracked unit, distorted bracket, damaged wiring or unsuitable installation. A scan reads available fault information; physical inspection and further testing may be needed to establish the cause. Include known damage and unfinished repairs. Buying a replacement solely from a sensor-related fault code can leave the original problem unresolved.

Which work may be needed

Tell us which side is affected, the exact Blind Spot Assist message and any rear bumper, paint, towbar or mirror work. The mirror indicator and rear radar are different components; a dark lamp does not diagnose the cause.

A diagnostic scan supplies fault information, not proof of physical aim or damaged hardware. Mounting, repair condition, wiring and compatibility can need further checks.

The centre blind-spot radar calibration rate is £162 including VAT. Replacement configuration is separate at £226.80 including VAT. Neither price supplies or fits a radar, and the configuration rate is not an automatic calibration bundle.

Work to one or both sides depends on the vehicle and required procedure. Do not assume two compulsory charges or both sensors included in one repair package. Send existing findings for a quote covering the actual work.

Mercedes calibration prices

A Blind Spot Assist fault is normally one system: the blind spot radar, with a second line only if the same knock disturbed something else in the bumper, like the parking sensors. Rates are the same at every service centre, per system, shown inc VAT with the net figure alongside. Your total is confirmed in writing before anything is booked.

Calibration — per system

Service At a service centre
Front camera calibration £162 inc VAT (£135 +VAT)
Front radar calibration £162 inc VAT (£135 +VAT)
Blind spot radar calibration £162 inc VAT (£135 +VAT)
360° / surround camera calibration £162 inc VAT (£135 +VAT)
Reversing camera calibration £206.40 inc VAT (£172 +VAT)
Parking sensor calibration £184.80 inc VAT (£154 +VAT)

Coding a replaced part to your vehicle

Service At a service centre
Front radar replaced £232.80 inc VAT (£194 +VAT)
Front camera replaced £229.20 inc VAT (£191 +VAT)
Blind spot radar replaced £226.80 inc VAT (£189 +VAT)
Reversing camera replaced £213.60 inc VAT (£178 +VAT)
  • When your job needs a diagnostic pre-scan, it's £54 inc VAT (£45 +VAT), itemised separately. It reads available fault information; finding the cause may require further investigation. A post-scan is a separate operation.
  • Two or more systems in one visit: the highest-priced system is full price, each additional system is 35% off at a centre. Scans aren't part of the discount. Front camera and front radar together come to £267.30 inc VAT (£222.75 +VAT).
  • Replacement configuration and calibration are different operations. The work required depends on the vehicle and what the installer has already completed. Configuration prices do not include supplying or fitting a replacement part, or an automatic calibration bundle.
  • Unsuccessful work, further investigation or a return visit may carry charges, including at a service centre. The appointment terms and written quote set out the work and applicable charges before booking.
  • Mobile calibration is available for garages and bodyshops with workshop conditions. Ask us.

Get your Mercedes' Blind Spot Assist sorted

Send your registration and a line on what's happened. We come back with the itemised quote, the nearest of 80+ UK service centres, and the soonest slot.

  • Per-system pricing, from £162 inc VAT.
  • Your quote is confirmed in writing before anything is booked.
  • Keep the calibration result with your repair records.
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Frequently asked questions

Rear work can affect radar mounting, the material in front of it, wiring or other components. Calibration requirements depend on the vehicle and repair; the timing of the warning does not prove aim is the cause. Include the bodyshop's findings and whether parts were removed, painted or replaced.

The centre blind-spot radar calibration rate is £162 including VAT. Replacement configuration is separate at £226.80. Neither supplies or fits a radar. Work to one or both sides depends on the vehicle and procedure; do not assume either a two-sensor package or two compulsory charges.

A one-sided message can involve the radar, installation, wiring or another component. The mirror indicator is not the sensing radar itself. Report which side and whether the symptom is a dashboard message, missing lamp or unexpected warning. A scan is evidence for investigation, not proof of physical alignment.

Not always. Fitted equipment, installation and the vehicle's requirements matter. Include when the towbar was installed, any associated electrical work and when the warning began. Calibration should not be assumed to be the remedy for a configuration or wiring fault.

The workshop needs the correct vehicle procedure, suitable equipment and any required diagnostic access. Send your registration, exact warning, repair history and location for a quote and appropriate appointment. Support depends on the particular system and task, not simply the badge on the car or the equipment brand.

Other Mercedes ADAS warnings we cover

A knock hard enough to upset a rear radar isn't always the only thing wrong. If other warnings arrived with it, one visit covers them, priced per system.

  • Distronic Fault

    The front radar behind the star badge that runs Distronic and Active Brake Assist. A separate sensor with its own calibration.

  • Collision Repair Recalibration

    When a body shop returns the car with several panels replaced, each disturbed sensor needs its own calibration line.

Book your Mercedes' ADAS calibration

Send your registration and what's been done. We come back with the price, the nearest service centre, and the soonest slot.

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