12 51 001 Replacing wiring harness section for engine (N54)

Necessary preliminary tasks 

• Read out fault memory of DME control unit
• Turn off ignition
• Disconnect BATTERY NEGATIVE LEAD
• Partially remove WIRING HARNESS  for ignition coils and injectors
• Remove INTAKE AIR MANIFOLD
• Remove front UNDERBODY PROTECTION
• Remove rear UNDERBODY PROTECTION

Release bolts along line (1).

Tightening torque 12 90 1AZ .

Remove electronics box cover.

Fig 1: Identifying Electronics Box Cover Mounting Bolts

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Unlock battery positive lead (1), detach and lay to one side.

Release locks (2) in direction of arrows and pull control unit upwards slightly.

Fig 2: Opening Control Unit Locks

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Pull control unit (1) upwards slightly until plug (2) can be released from control unit in direction of arrow.

Unlock plug (2) and detach from control unit (1).

Fig 3: Pulling Control Unit Upwards

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Unlock and detach all plugs from engine wiring harness in electronics box (1).

Unclip rubber grommet hold-down devices (2) and (3) and release engine wiring harness from electronics box.

Installation: 

Make sure rubber grommets are correctly seated (watertightness).

Fig 4: Identifying Electronic Box With Rubber Grommet Hold Down Device

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Long plug:

Press in retaining lugs and withdraw lock (1) in direction of arrow from plug housing.

Fig 5: Removing Locks From Plug Housing

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Press locking tabs (1) in direction of arrow and pull contact carrier (2) out of housing.

Fig 6: Pressing Locking Tab

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Press locking tab (1) in direction of arrow and pull contact carrier (2) out of housing.

Fig 7: Pressing Locking Tab

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Unlock locking tabs (1) in direction of arrow and pull contact carrier (2) out of housing.

Fig 8: Opening Locking Tabs

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Short plug 

Press in retaining lugs (1) and withdraw lock (2) in direction of arrow from plug housing.

Fig 9: Removing Locks From Plug Hosing

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Press locking tabs (1) in direction of arrow and pull contact carrier (2) out of housing.

Fig 10: Pressing Locking Tab

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Unlock locking tabs (1) in direction of arrow and pull contact carrier (2) out of housing.

Press locking tab (1) in direction of arrow and pull contact carrier (2) out of housing.

Fig 11: Identifying Locking Tabs And Contact Carrier Out Of Housing

Fig 12: Opening Locking Tabs

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Short connector:  Press in retaining lugs (1) and withdraw lock (2) in direction of arrow from connector housing.

Fig 13: Pulling Slide Out Of Housing

Press locking tabs (1) in direction of arrow and pull contact carrier (2) out of housing.

Fig 14: Identifying Locking Tabs And Contact Carrier

Unlock locking tabs (1) in direction of arrow and pull contact carrier (2) out of housing.

Fig 15: Identifying Locking Tabs And Contact Carrier Out Of Housing

Unclip cable duct upper section (1) and expose wiring harnesses.

Fig 16: Locating Wiring Harness In Cable Duct Upper Section

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Unscrew screws (1).

Tightening torque 12 90 4AZ .

Remove cable duct (2).

Fig 17: Identifying Cable Duct And Screws

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Release wiring harness from clips and retainers.

Feed out wiring harness and remove.

Installation: 

Check wiring harness routing.

Check plug connections for correct seating.