Why does the Mercedes Benz parking brake light stay on continuously?

In this article, we find out why the Mercedes Benz parking light stays on? And we also learn about different parking brake systems used in Mercedes Benz cars. Finally, we explain some methods to troubleshoot parking brake malfunctions.

Why does the Mercedes Benz parking brake light stay on continuously?

The parking brake light in Mercedes Benz cars stays on to indicate that the parking brake is not released completely. A parking brake is present in the vehicle to protect the transmission and avoid unnecessary stress. For example, when the vehicle is parked on an inclined surface, the parking brake can secure the vehicle against rolling away and the transmission is not under mechanical load. 

The parking brake is located on the rear wheels. When the driver applies the parking brake, the parking brake indicator lamp turns on in the instrument cluster. The parking brake lamp is turned off when the parking brake is released and the vehicle can move forward. 

The parking brake light would not stay on when the vehicle is moving as the rear brakes can still be in contact with the brake disc. Driving the vehicle when the parking brake lamp is On can overheat the rear brakes and damage the brake system.

Mercedes Benz uses two types of parking brakes, they are Mechanical and electric parking brakes. Mechanical parking brakes are only found on old Mercedes Benz models. 

All the latest Mercedes models on sale today implement an electronic parking brake. Regardless of which type, a parking brake lamp is present in the instrument cluster to indicate malfunction of parking brake systems.

How does a Mechanical parking brake system work?

The mechanical parking brake system is found on old Mercedes Benz models like W212 E class, W204, Class. Like the name suggests, a Mechanical parking brake system consists of an independent brake lever located in the driver’s footwell. 

The brake lever is used to operate independent drum brakes on the rear axles. The spring-loaded brake lever is connected to the rear drum brake by a mechanical cable. 

There is a release lever situated on the dashboard, when the release lever is pulled the lever returns to the open position and the parking brake is detached. The electronic switch is used to recognise the released and braked position of the lever. It is located on the lever in such a way that when the lever is pressed, the switch is open and the parking lamp gets turned on in the cluster and vice versa. 

What are the causes of parking brake lamps staying on in the mechanical parking brake system?

  • Fault in Brake lever- If the parking brake lever does not return to an initial position fully due to weak spring load or jammed lever, the brake will be slightly touching the drum and the parking brake lamp will stay on in the instrument cluster.
  • Fault in release Mechanism- The release handle is broken or damaged and cannot release the parking brake completely. The release handle is connected to the parking brake lever with the help of a cable. The cable of the release handle can get jammed and pulling the handle with excessive force can break it.
  • An electrical fault in the switch– the parking brake switch is used to determine the position of the parking brake lever. The switch is connected to the signal actuation and acquisition control unit by electrical lines. Open or short circuits of the electrical lines can cause the parking brake lamp to stay on continuously even when the brake is released completely.

How does an electronic parking brake system work?

The electric parking brake system found in all the latest Mercedes Benz models uses two electric actuator motors to engage both rear axle brake callipers and apply the parking brake. 

There is no separate drum brake system found on the Mechanical parking brake system. Both the electronic motors are connected to the parking brake control unit by independent electrical lines.

 When the brake is fully applied, the electric parking brake control unit sends a CAN signal to the instrument cluster and the light is turned on. There is no mechanical release handle, the driver simply presses the parking brake release switch and the control unit will send a signal to the electronic actuators and release the parking brake. In some models, the electronic parking brake function is integrated with the ESP control unit. 

During brake pads replacement on the rear axle, the electrical actuator motors can be locked in assembly position and after replacement, the electronic parking brake releases the motor. The brake pad replacement option can be selected from the instrument cluster via the workshop menu. 

As the electronic parking brake utilizes service brakes of the vehicle, the condition of the rear brake pads must be okay, worn-out brake pads can cause the vehicle to roll.

What are the Malfunctions in electronics parking brakes?

  • Fault in Motors- the electronic actuator motors can get jammed and keep the parking brake engaged even when the control unit is sending an actuation signal. A stuck actuator can damage the rear brake pad and brake calliper. Continuing to drive the vehicle in such a state will also overeat the brake disc.
  • Fault in control unit- the electronic parking brake control unit is connected to CAN bus communication system, the fault control unit can no longer send or receive signals. The electronic parking brake will be inoperative in this state. 
  • Fault in release switch- electronic switch is used to engage and disengage the parking brake. If the switch is faulty, the control unit will no longer receive the status of the electronic parking brake release switch. The electric parking brake will stay inoperative in such cases and the parking brake lamp is continuously on in the instrument cluster. In vehicles with informative displays, an Electric parking brake malfunction message also appears on the screen.

How do rectify faults in the event of a parking brake malfunction?

Faults in both mechanical and electrical parking brakes are easy to identify. After visiting the authorized workshop technician can connect the Xentry diagnosis system and check the actual values of the electronic parking brake systems. Fault code is usually logged in the control unit fault memory and after performing checks, replacing the faulty part will rectify the malfunction.

Mechanical parking brake issues are mostly in the parking brake lever and release mechanics. Over time, the spring gets weaker and the brake lever must be replaced to rectify the fault. The total cost of repairs in the mechanical parking brake system is lower than compared of the electronic parking brake system. The only exception is the S class W221 which had a combination of the electronic control unit and mechanical actuator to apply the parking brake. The complete parking brake system needed replacement after 100,000 actuation.

Following are some tips to troubleshoot the parking brake lamp stays on:-

  • If Electronic parking brakes are present on the vehicle and the parking brake lamp stays on then actuate the electronic parking brake switch multiple times and cycle the position from engaging to disengage. Toggle the ignition of the vehicle, this will reset the parking brake position.
  • If the message release parking brake appears in the cluster, press the parking brake switch once to release the brake and continue to drive the vehicle.
  • Electronic motors have mechanical release behind the cover, remove the cover and use an Allen key to retract the actuator. Make sure the ignition is turned off.
  • For mechanical parking, brakes do not apply excessive force on the release handle if the lamp stays on. Check the electrical coupler near the parking brake lever.
  • Operate the parking brake lever back and then use the release handle to disengage the parking brake.

If the above tips do not rectify and the fault is still present then consult the nearest workshop for further diagnosis.

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Parking brakes are very crucial for the vehicle as it prevents excessive load on the transmission of the vehicle. They also act as an anti-theft measure and vehicles will not move until the brakes are released, Mercedes Benz also has an auxiliary power supply for the operation of the electronic parking brake if the main battery is discharged completely. Therefore, there should be no faults in the parking brake systems. 

FAQs:Why does the Mercedes Benz parking brake light stay on continuously?

Why is my parking brake light not turning off?

The parking light bulb is not turning off because the parking brake is not released completely. There can also be a malfunction in the parking brake release lever that can cause a partial release of the parking brake.

How do you reset the parking brake light on a Mercedes?

There is no procedure to reset the parking brake light without rectifying the fault. After the fault is successfully resolved, the parking light is reset after a complete operation of the parking brake.

How do I reset my parking brake light?

To reset the parking brake light, start the vehicle and first engage the parking brake and then disengage, repeat the procedure couple of times to reset the parking light. Consult the workshop if the parking light stays on even after operating it multiple times.