Mercedes knock sensor replacement, made easy

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Our expert insights into knock sensor replacement

What does a knock sensor do?

The knock sensor is bolted directly onto the outside of the engine block and is used to detect vibrations and detonation “knock” noises from the engine to prevent engine damage.

What are the symptoms of a bad knock sensor?

Below are the top three symptoms that could indicate you need to replace your knock sensor:

  • Engine pre-detonation known as “pinking” or knocking

  • Reduced engine power

  • Increased fuel consumption

What happens when we do a knock sensor replacement on your car?

Our certified mechanics will:

  • Perform a diagnostic check to discover any fault codes coming from the knock sensor and other related parts of the engine.

  • Once they confirm that the knock sensor is faulty, they will fit a replacement knock sensor.

  • Once replaced, the mechanic will start the engine and recheck for fault codes.

Daniel, from LondonDaniel, from London

Hey Fixter, what causes a knock sensor to break?

Knock sensors can fail due to incorrect mounting, corrosion, breaks in wiring or mechanical damage. Knock sensors are quite fragile, therefore you should take proper care of it to maintain its life for longer.

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Want to learn more about Mercedes knock sensor replacement?

What does a knock sensor do?

The knock sensor is located on the outside of the engine block. Its job is to record knocking noise from the engine in order to prevent engine damage.

The knock sensor "listens out for" vibrations from the engine block and converts these into electrical signals. The signals are filtered and evaluated in the engine’s control unit. If the vibrations are determined to be outside of the predefined ‘normal’ limits, the engine management control unit will alter the ignition timing until it returns to within the correct limits.

Mercedes-Benz

Mercedes-Benz is a German global car manufacturer and a division of Daimler AG. They were established over 100 years ago in 1926 and have grown to be the biggest selling premium vehicle brand in the world.

The number of Mercedes cars on the road in the UK continues to rise, reaching 1.9million by the final quarter of 2018. There are almost 5 times as many Mercedes cars on the road as there were in 1995, showing just how popular this marque has grown to be.

Helping these powerful statistics on their way, the Mercedes A-Class was announced as the 8th best selling car in the UK in 2018. The premium family hatchback is vying for position against the ever-popular VW Golf—the current leader in this class.

Premium executive models of every shape and size

Mercedes deliver hatchbacks, saloons, estates and coupés at every size from their A- to E-Class ranges, as well as executive SUVs, the V-Class MPV, and of course, a more than desirable selection of convertibles and roadsters.

With prices rising to well over £100k, Mercedes cars are a great contender as the executive car of choice.

Mercedes-Benz: Giants of Formula One

Mercedes has always been a keen player within the F1 championship, taking their first 2 titles back in 1954 and 1955. Through the 1990s they joined forces with McLaren as an engine provider and part owner, bringing titles for both Mika Häkkinen and Lewis Hamilton and a constructors championship in 1988.

Their current and outright domination of the sport began in 2014, as a team in their own right, it has featured 5 straight constructors titles, with Lewis Hamilton taking 4 world championships and Nico Rosberg taking the other in 2016.

How often should a knock sensor need replacing?

Replacing a knock sensor is not part of routine car maintenance so should only need to be fixed when it breaks or begins to fail. On most modern vehicles, the knock sensor should last over 150,000 miles or the lifetime of the vehicle.

The law, vehicle regulations and your MOT

A fault with the knock sensor will often illuminate the Engine Management Light in your car. Your vehicle will fail its MOT if your Engine Management Light remains on when the engine has been started. Under the new MOT rules, it is now classed as a major fault so will need to be fixed before a mechanic can pass your car. Therefore it’s crucial that you keep an eye out for engine warning lights and have your car inspected by one of our vetted mechanics when necessary.

What happens when we do a knock sensor replacement on your car?

Our certified mechanics will:

  • Perform a diagnostic check to discover any fault codes coming from the knock sensor and other related parts of the engine.

  • Once they confirm that the knock sensor is faulty, they will fit a replacement knock sensor.

  • Once replaced, the mechanic will start the engine and recheck for fault codes.

When should a knock sensor be replaced?

You should have your knock sensor looked at as soon as you notice any of the related symptoms, such as an illuminated engine warning light, reduced engine power or poor fuel economy. Because your knock sensor plays a vital role in preventing engine damage and in the safe and efficient running of your car, it’s very important to have it fixed as soon as possible.

What are the signs of a bad knock sensor?

Usually, there a few signs you can look for:

  • Engine pre-detonation known as “pinking” or knocking

  • Engine warning light comes on

  • Reduced engine power

  • Increased fuel consumption

How often should you replace your knock sensor?

Replacing a knock sensor is not part of routine car maintenance so should only need to be fixed when it breaks or begins to fail. On most modern vehicles, the knock sensor should last over 150,000 miles or the lifetime of the vehicle.

What happens during a knock sensor replacement?

During the repair our certified mechanics will:

  • Perform a diagnostic check to discover any fault codes coming from the knock sensor and other related parts of the engine.

  • Once they confirm that the knock sensor is faulty, they will fit a replacement knock sensor.

  • Once replaced, the mechanic will start the engine and recheck for fault codes.

What is the average life of a knock sensor?

On most modern vehicles, the knock sensor should last over 150,000 miles or the lifetime of the vehicle.

Can you drive with a broken knock sensor?

You should not drive with a bad knock sensor. If you continue to drive with a failing sensor, serious damage could be done to your engine, causing an expensive repair or replacement. As well as this a bad knock sensor will greatly reduce your cars power and fuel economy. To save yourself time and money down the line we recommend refraining from driving and getting the issue fixed as soon as possible.

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