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Knock Sensors Replacement
 
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Pelican Technical Article:

Knock Sensors Replacement

Steve Vernon

Time:

30 minutes30 mins

Tab:

$35 to $70

Talent:

**

Tools:

E10 socket, torque wrench

Applicable Models:

Mercedes-Benz C350 (2008-14)
Mercedes-Benz GLK350 (2010-14)

Parts Required:

New knock sensors sensor, intake manifold gasket

Hot Tip:

Don't work on a hot engine

Performance Gain:

Piece of mind on engine knock

Complementary Modification:

New injectors

There are two knock sensors on the Mercedes C350 and they play an important part of the engine management system. The sensors detect knock or ping in the motor, which is pre detonation and can cause serious and expensive damage to the motor. If knock is detected the sensor will tell the management system of the engine to severely retard the ignition. Besides an error code you will notice a lack of power and throttle response.

The sensors are easy to replace once you get access to them. Unfortunately, you will need to remove the fuel rail, injectors and intake manifold. Please see our articles on how to perform this work.

Note: The knock sensors are torque sensitive and over or under torquing them will result in incorrect readings from the sensors and poor performance from the motor. The sensors must be torqued to 20Nm on the 272 engine.

You will need to remove the engine covers (red and yellow arrows) and air intake ducts (green arrows) to perform this work.
Figure 1

You will need to remove the engine covers (red and yellow arrows) and air intake ducts (green arrows) to perform this work. Please see our article on engine cover removal for additional assistance.

Next you need to remove the intake manifold to get the motor to this stage.
Figure 2

Next you need to remove the intake manifold to get the motor to this stage. Please see our article on intake manifold removal for step-by-step instructions.

With the manifold removed you can see the two knock sensors in the V of the motor (red arrows).
Figure 3

With the manifold removed you can see the two knock sensors in the "V" of the motor (red arrows). There is one knock sensor for each bank of cylinders.

The clips used to hold the wiring connection to the sensors is quite beefy; squeeze in both sides of the clips and wiggle the connection off (red arrows).
Figure 4

The clips used to hold the wiring connection to the sensors is quite beefy; squeeze in both sides of the clips and wiggle the connection off (red arrows).

Use an E10 socket and remove the old sensor (red arrow).
Figure 5

Use an E10 socket and remove the old sensor (red arrow).

The knock sensors are torque sensitive and over or under torqueing them will result in incorrect readings from the sensors and poor performance from the motor.
Figure 6

The knock sensors are torque sensitive and over or under torqueing them will result in incorrect readings from the sensors and poor performance from the motor. The sensors must be torqued to 20Nm on the 272 engine.


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Page last updated: Thu 2/23/2017 03:00:54 AM