Knock Sensor: Service and Repair

12 14 600 Removing/replacing Knock Sensors (N53, N54)

Special tools required:







WARNING:
Disconnect negative battery terminal (risk of fire due to short-circuiting on removal).

Electric fuel pump starts up automatically when door is opened.

Carry out installation work on fuel system only with coolant temperature below 40°C.







IMPORTANT:
Adhere to conditions of absolute cleanliness when carrying out repair work on the high-pressure fuel system.

Introduced contaminants can cause malfunctions in the system.

- Do not allow any dirt particles or foreign bodies to get into the system.
- Remove all traces of dirt before removing pipes or individual components.
- Use only fluff-free cloths.
- Seal all fuel system openings with protective caps or plugs.







IMPORTANT:
Aluminium screws/bolts must be replaced each time they are released.

Aluminium screws/bolts are permitted with and without colour coding (blue).

For reliable identification:

Jointing torque and angle of rotation must be observed without fail (risk of damage).

Necessary preliminary tasks:
- Read out fault memory of DME control unit.
- Switch off ignition.
- Remove intake plenum.







NOTE: Illustration shows N54.







Recycling:
Fuel escapes when fuel lines are detached.
Catch and dispose of escaping fuel.
Observe country-specific waste disposal regulations.







Unlock connector (1) and remove.

Unlock and detach fuel line (2).

Catch and dispose of escaping fuel.







Seal fuel lines with special tools 13 5 281 and 13 5 282 .







Slacken nut (1).

Close off fuel line connection of high-pressure pump with a matching plug from special tool set 32 1 270.

Release screw (2).

Installation note:
- Replace aluminium screw.

Remove feed line (3).







Seal feed line with matching plug from special tool kit 32 1 270.







Unlock connector (1) and remove.







Release screws on both knock sensors (1) and remove knock sensors (1).

Installation note:
- Replace aluminium screws.
- Tightening torque 12 14 1AZ.







Installation note:
Clean contact surface of knock sensors on engine block.







Installation note:
Pre-install feed line (3).

In so doing, tighten screw connection hand-tight only (it must still be possible to move the line at the holder).

IMPORTANT:
Sequence of screw connection must be observed.
- Tighten nut (1). Tightening torque 13 53 6AZ.
- Tighten screw (2). Replace aluminium screw. Tightening torque 13 53 9AZ.







NOTE:
Reassemble the vehicle.
Check stored fault messages.
Delete fault memory.