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Your warning light guide

Your Mercedes-Benz is equipped with some of the most advanced automotive technology that is designed to deliver a drive like no other whilst keeping you, your passengers and other road users safe.

These state-of-the-art systems use sensors to indicate any issues in their operation, which you will be alerted to by the appearance of warning lights on your dashboard. To help you understand the most common warning lights, we have compiled this simple guide based on a traffic light system.

To help you understand the most common warning lights, we have compiled this simple guide based on a traffic light system.

RED: Stop the car as soon as it is safe to do so.

YELLOW: Action required.

GREEN: For information only.

Whilst there is no need to be overly alarmed, it is important that you respond to each warning light accordingly to not only reduce any damage to your vehicle but to ensure that it continues to drive safely.

At all times please be assured that we are here to assist you so, if there is any action that you’re unsure about or a repair is required, your local Mercedes-Benz South Wales aftersales team will be on hand to make sure everything is safe and in optimum order.

Red warning lights

Airbag and Seatbelt System

If the warning symbol doesn't illuminate when the ignition is turned on or if it lights up either continuously or repeatedly during a journey then you will need to contact a Mercedes-Benz authorised repairer immediately.

Bonnet Icon


Firstly please check that the bonnet is closed properly.

If the light does not disappear, please get in touch with an authorised repairer.​

Boot lid icon

Boot Lid

Check the boot lid is closed properly. If the light disappears this is a normal function.

If the light does not disappear, you will need to seek the assistance of an authorised repairer.

Brake System Logo

Brake System

Check if the handbrake is on and, if so, release it. You may continue to drive as normal if the warning light disappears.

If it remains on, you will then need to check the brake fluid level and top up accordingly*.

Please contact Roadside Assistance if the light continues to stay on.

Engine Cooling System Logo

Engine Cooling System

Switch off the engine immediately and wait until the engine has cooled down.

If applying your own coolant, please remember that your car’s cooling system is pressurised. If the light remains on contact Roadside Assistance.

We would recommend that the coolant is topped up by a Mercedes-Benz technician. Therefore please drive to your nearest authorised Mercedes-Benz Repairer whilst avoid high loads on the engine and maintaining the coolant temperature below the red marking.

Engine Oil Pressure Logo

Engine Oil Pressure

Switch off the engine immediately and don’t restart. Check the oil level. If it’s ok, contact Roadside Assistance.

If it is low, top up accordingly*. Restart your engine and then switch off after running for five seconds. You will need to get in touch with Roadside Assistance if the light remains on.

Mercedes SOS logo

Mercedes SOS

This warning light shows that at least one of the main functions of the Mercedes me connect system or SOS emergency call system have malfunctioned.

Please consult your nearest Mercedes-Benz Retailer.

Power Steering System warning light

Power Steering System

If the steering feels unsafe or distinctly different to normal, please pull over when safe to do so and contact Roadside Assistance.

Otherwise continue driving to your nearest Mercedes-Benz authorised repairer.

Recharge ad blue warning ligjt

Recharge AdBlue (Red)

The red warning light appears when there is no AdBlue range left.

Please stop the car as soon as it is safe to do so.

Seatbelt buckles warning light

Seatbelt Buckles

Check that the driver and front passenger have both fastened their seatbelts properly. If the light disappears, this is a normal function. 

If the light does not disappear contact an authorised repairer.​

The car will not restart once the ignition is turned off, so the system will need a full top-up* before the car can be restarted.*

vehicle charging system warning light

Vehicle Charging System

This light indicates an alternator or electrical system fault in the vehicle so, in the first instance, switch off all consumer electrical products that may further drain the battery.

Let the engine run for a few minutes or drive for approximately 10 minutes or so to allow for battery regeneration. If you cannot start the engine contact Roadside Assistance.

*Refer to owner’s manual or seek professional assistance.

The information on warning lights on this page does not apply to electric cars. Please consult your owner's manual.

Yellow warning lights

Active Brake Assist Warning Light

Active Brake Assist

If this warning light appears, all or some of the following Active Brake Assist functions may not be working: distance warning, autonomous braking, situation dependent braking assist and evasive steering assist.

If all sensors are clear and free of dirt, please consult an authorised repairer.

Active Lane Assist Warning Light

Active Lane Assist

This light will appear when lane assist is switched on and road markings cannot be detected.

If it is accompanied with a ‘system fault’ message then you will need to contact an authorised repairer.

Airbag and seatbelt system warning light

Airbag and Seatbelt System

A fault is likely to have occurred in the airbag or seatbelt system, so you will need to get this rectified immediately as, failure to do so, may mean that it won’t operate in the event of an accident.

ABS Warning light

Anti-Lock Brake System

If this light illuminates, it will indicate the safety systems are currently not available which result in longer emergency braking distances so you will need to drive carefully to an authorised repairer for investigation.

Attention Assist Warning Light

Attention Assist

You should take a break if this warning light appears as the car has detected driver fatigue or a lack of concentration.

Please consult an authorised repairer if the light remains on.

Automatic Gearbox Warning Light

Automatic Gearbox

A message may appear if a gearbox malfunction is detected. Follow the instructions and drive to an authorised repairer immediately if is safe to do so. 

If this is not possible or you are asked to stop the vehicle and select P, you will need to contact Roadside Assistance.

Brake Pad Monitoring Warning Light

Brake Pad Monitoring

This indicates that your car’s brake pads have reached their wear limit and braking may be limited. Get an authorised repairer to check their condition.

Cruise Control Warning Light

Cruise Control

It is a normal function for this light to appear when the cruise control system is activated.

Refer to the owner’s manual  for an explanation of the operation of the system.​

Emissions Control Light

Emissions Warning Light

Emissions Control Light

There could be an issue with the engine, exhaust system or fuel system if this light comes on.

Firstly remove the key for 30 seconds then reinsert and start the engine. If the light disappears, the problem is rectified but we recommend getting things checked at an authorised repairer.

You will need to contact Roadside Assistance if the light returns and the power is down. Similar action is required if the warning light flashes and the power is down and the vehicle is vibrating.

You should drive to an authorised repairer for assistance if the power isn’t down but the light stays on or continues to flash even if your car isn’t vibrating.

Engine Management Warning Light

Engine Management Warning Light (Diesel Engines Only)

If it is perfectly normal for this light to appear for a few seconds when the ignition is turned on initially.

If the light appears whilst the engine is running, it is likely that there is an engine management fault so please drive slowly to your nearest authorised repairer

Engine Oil Level Warning Light

Engine Oil Level

If permanently illuminated, this indicates the oil level has either dropped or exceeded the recommend levels.

If the former, please top up above the minimum level.

Should you have exceeded the maximum level, you will need to contact an authorised repairer as engine damage could be caused by excess oil.

This light may also highlight the oil level sensor has malfunctioned. If the oil level is at the correct level but the light remains on then the oil level sensor may have malfunctioned so ​please consult our workshop team.

Fuel Warning Light


You will need to refuel as soon as possible if this light appears as it indicates that the fuel level has dropped into the reserve.

If you do have fuel, please check that your vehicle’s fuel cap is not loose.

Headlight range control warning light

Headlight Range Control

Contact an authorised repairer as a fault has been detected.

Headlight warning light

Headlight Warning

You vehicle’s headlights are still on so you will need to turn the light switch position to off or auto.

If the light remains on, there may be a fault with the lighting system so you may need to consult an authorised repairer to resolve.

Hold handbrake system warning light

Hold Handbrake System

The hold function has been activated. This is normally activated by pressing hard on the brake while the transmission is in drive mode. To disengage hold, press the accelerator pedal.

If this continues to illuminate, please seek an authorised repairer.

dipped beam warning light

Low/High Beam

This indicates whether the headlights are on low or high beam. If set to automatic, they will automatically appear when darkness falls.

Parking Sensor Malfunction warning light

Parking Sensor Malfunction

This alerts you to a deactivation of the PARKTRONIC park assist system, which may be due to signal interference, dirty sensors or a malfunction.

Turn the vehicle on and off whilst checking that the sensors are clean. If the problem persists, please contact an authorised repairer.

Power Steering System

This light may appear if your battery has been disconnected or discharged or if your vehicle has been jump started.

In the first instance, please try turning your steering wheel fully to the left, then fully to the right and driving a short distance at low speed. Whether this clears the light or not, we recommend getting the car checked at an authorised repairer. 

If you’re unable to carry out the aforementioned procedure then please contact Roadside Assistance. 

Rear Fog Lights Warning Light

Rear Fog Lights

​You will receive this warning when the rear fog lights are switched on. These only need to be in use during foggy conditions as they might dazzle drivers travelling behind.

Smart key warning light

Smart Key

Several issues may have arisen with your smart key if this light appears. These include the battery discharging, the key not being detected or an alert to take your key when leaving the vehicle – an event that may be accompanied by a warning sound.

Consult a qualified authorised repair.

Tyre pressure monitoring light

Tyre Pressure Monitoring

Low tyre pressures or a missing/faulty wheel sensor are the likely causes if this light appears.

The system will need to be checked by an authorised repairer if the tyre pressures are ok and the light is remains on.

Windscreen washer fluid warning light

Windscreen Washer Fluid Level

This light simply means that the windscreen washer fluid reservoir needs filling.

Refer to the owner’s manual for guidance.

*Refer to owner’s manual or seek professional assistance.

The information on warning lights on this page does not apply to electric cars. Please consult your owner's manual.