12 51 001 Wiring harness - replacing engine section (M73)

Switch off ignition.
Remove battery negative line.
Remove complete splash guard.
Remove fan wheel, refer to 11 52 020 REMOVING AND INSTALLING OR REPLACING FAN COUPLING (M73) .

Rotate screws through 90°. Remove cover from cylinder head cover.

Fig 1: Removing Cover From Cylinder Head Cover

Press down detent (2) and remove plug connection (1).

Fig 2: Pressing Detent And Removing Plug Connection

Open clips (1).

Unfasten hose clip (2) from auxiliary hose for air pump.

Disconnect plug-in connection (3).

Unfasten hose clip (4).

Remove upper section of right suction filter housing with mass air flow sensor.

Fig 3: Removing Right Suction Filter Housing Upper Section With Mass Air Flow Sensor

Open clips (1).

Unfasten hose clip (2) from auxiliary hose for air pump.

Disconnect plug-in connection (3).

Remove upper section of left suction filter housing with mass air flow sensor.

Fig 4: Removing Right Suction Filter Housing Upper Section With Mass Air Flow Sensor

Unfasten screws in retaining brackets (1 and 2) on cylinder head cover. Remove retaining brackets.

Fig 5: Removing Retaining Brackets

Unfasten connections on left ignition coils (1 and 2).

Fig 6: Removing Left Ignition Coils Connections

Disconnect plug connection on tank vent valve.

Fig 7: Disconnecting Tank Vent Valve Plug Connection

Unfasten screw connection on positive battery line from positive battery terminal.

Fig 8: Releasing Positive Battery Terminal Screws

Disconnect plug connection (1) from camshaft sensor and plug connection (2) from vacuum control unit.

Fig 9: Disconnecting Camshaft Sensor And Vacuum Control Unit Plug Connection

Disconnect left plug connections (1 and 2).

Fig 10: Disconnecting Left Plug Connections

Remove tank vent valves (1 and 2) with bracket.

Fig 11: Removing Tank Vent Valves (1 And 2) With Bracket

Disconnect connections on alternator, unfastening cable ties (1 and 2).

Fig 12: Disconnecting Alternator Connections And Releasing Cable Ties

Connections here illustrated on removed alternator.

Unfasten plug connection (1)

Unfasten nut (2).

Tightening torque, refer to ENGINE - TIGHTENING TORQUES .

Fig 13: Releasing Plug Connection And Nut

Unclip diagnosis connector from bracket.

Fig 14: Removing Diagnosis Connector From Bracket

Disconnect right plug connections (1 and 2).

Fig 15: Disconnecting Right Plug Connections

Disconnect plug connections on actuator motors for throttle valves.

Fig 16: Disconnecting Actuator Motors Plug Connections

Disconnect plug connection on cable ducts (1 and 2).

(1) Knock sensor on cylinder (1 to 3)
(2) Knock sensor on cylinder (4 to 6)

Fig 17: Disconnecting Cable Ducts Plug Connection (Knock Sensor On Cylinder 1-3 And 4-6)

Disconnect plug connection on cable ducts (1 and 2).

(1) Knock sensor on cylinder (7 to 9)
(2) Knock sensor on cylinder (10 to 12)

Fig 18: Disconnecting Cable Ducts Plug Connection (Knock Sensor On Cylinder 7-9 And 10-12)

Unfasten nut on rear cable duct.

Fig 19: Removing Rear Cable Duct Nut

Unfasten nut.

Fig 20: Removing Nut

Unfasten plug connection on injector valves.

Fig 21: Disconnecting Injector Valves Plug Connection

Open fast release connections on tank vent valves, press down interlock (1) and remove hose (2).

Fig 22: Pressing Interlock And Removing Hose

Unclip oil drip tray.

Remove fan, refer to 11 52 020 REMOVING AND INSTALLING OR REPLACING FAN COUPLING (M73) .

Fig 23: Removing Oil Drip Tray

Pressure hose from pressure pipe on non-return valve for air induction to cylinders 7-12.

Loosen hose clamp. Pull off hose.

Fig 24: Loosening Hose Clamp And Removing Hose (Cylinders 7-12)

Pressure hose from pressure pipe on non-return valve for air induction to cylinders 1-6.

Loosen hose clamp. Pull off hose.

Fig 25: Loosening Hose Clamp And Removing Hose (Cylinders 1-6)

Unfasten hose clip to remove pressure hose from air pump to pressure pipe. Pull off hose.

Fig 26: Removing Pressure Hose From Air Pump To Pressure Pipe

Unscrew and remove pressure pipe with bracket (1). Remove non-return valve for cylinders 1 -6.

Fig 27: Removing Pressure Pipe With Bracket

Unfasten plug connection from temperature sensor for coolant temperature.

Fig 28: Disconnecting Temperature Sensor Plug Connection

Unfasten plug connection (1) from oil level sensor and starter motor (2).

Fig 29: Disconnecting Oil Level Sensor And Starter Motor Plug Connection

Slide cable duct backwards to remove from front interlock (1) then lift it up (2).

At this point, the wiring harness is effectively removed, e.g. it was possible to remove the intake air manifold.

Fig 30: Removing Cable From Front Interlock

Unfasten plug connection on impulse sensor on crankshaft (flywheel) for DME of cylinder 1 - 6 (DME 1).

Installation:

Clip line from impulse sensor (2) into bracket (1).

Fig 31: Disconnecting Crankshaft Impulse Sensor Plug Connection - DME Cylinder 1 - 6 (DME 1)

Unfasten plug connection on impulse sensor on crankshaft (flywheel) for DME of cylinder 7-12 (DME 2).

Fig 32: Disconnecting Crankshaft Impulse Sensor Plug Connection - DME Cylinder 7 - 12 (DME 2)

Unclip lines from bracket on transmission bell housing.

Fig 33: Releasing Lines From Transmission Bell Housing Bracket

Installation:

Clip lines into bracket on the transmission bell housing.

Fig 34: Installing Lines To Transmission Bell Housing Bracket (1 Of 3)

Installation:

Clip lines into bracket on the transmission bell housing.

Fig 35: Installing Lines To Transmission Bell Housing Bracket (2 Of 3)

Installation:

Clip lines into bracket on the transmission bell housing.

Fig 36: Installing Lines To Transmission Bell Housing Bracket (3 Of 3)

Unfasten plug connection for position switch on automatic transmission.

Fig 37: Disconnecting Automatic Transmission Position Switch Plug Connection

Unfasten plug connection for shift unit on automatic transmission.

Fig 38: Disconnecting Automatic Transmission Shift Unit Plug Connection

Unfasten screws and remove cover of plug connections for left and right Lambda oxygen sensors. Mark (identify) plug connections and disconnect.

Fig 39: Removing Left And Right Lambda Oxygen Sensors Plug Connections Cover

Unclip wiring harnesses from left and right Lambda oxygen sensors on the heat shields.

Fig 40: Releasing Wiring Harness From Left And Right Lambda Oxygen Sensors

Unclip and remove wiring harness on transmission bracket.

Fig 41: Releasing And Removing Transmission Bracket Wiring Harness (1 Of 2)

Unclip and remove wiring harness on transmission bracket.

Remove heat baffle plates from left and right catalytic converters.

Extract complete wiring harness from vehicle underside.

Fig 42: Releasing And Removing Transmission Bracket Wiring Harness (2 Of 2)

Remove from top side of vehicle:

Disconnect cable tie on cylinder head of cylinder bank 1 -6

Fig 43: Disconnecting Cylinder Head Cable Tie (Cylinder Bank 1 -6)

Ground wires on cap of spring strut shock absorber: unfasten nuts.

Fig 44: Attaching Wires On Spring Strut Shock Absorber Cap

Unfasten screws in cover on electronics box. Tightening torque, refer to ENGINE - TIGHTENING TORQUES .

Fig 45: Releasing Electronics Box Cover Screw

Remove relays (1 to 3) with bracket.

Relays for Digital Motor Electronics (DME 1)
Relays for Digital Motor Electronics (DME 2)
(can be recognized because cross section of feed lines is greater than 2.5 mm2)
Relay for starter motor inhibit

Fig 46: Removing Relays With Bracket

Disconnect plug connection on temperature sensor for electronics box.

Fig 47: Disconnecting Electronics Box Temperature Sensor Plug Connection

Disconnect plug connections (1 to 4).

Control unit for Digital Motor Electronics for cylinders 1-6 (DME1)
Control unit for Digital Motor Electronics for cylinders 7-12 (DME 2)
Control unit for Electronic Transmission Control (EGS)
Control unit for Electronic Engine Power Control (EML)

Fig 48: Disconnecting Plug Connections (1 To 4)

Disconnect plug connections (1 to 4). Unfasten cable tie on back of cylinder head (cylinder bank 7-12).

Remove complete wiring harness.

Fig 49: Disconnecting Plug Connections (7 To 12)