12 63 520 Replacing main relay

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Switch off ignition.

Connect DIS Tester.

Release screws (1).

Remove electronics box cover.

Fig 1: Releasing Screws Of Electronics Box Cover

Courtesy of BMW OF NORTH AMERICA, INC.

Installation:

Correctly install wiring harness with grommet in electronics box cover (water tightness).

Hook cover (3) into hinges of underside of electronics box (1).

Then correctly install upper stop (2) above hinges on underside of electronics box.

Fig 2: Installing Cover Into Hinges Of Underside Of Electronics Box

Courtesy of BMW OF NORTH AMERICA, INC.

Arrangement:

Main relay of Digital Motor Electronics
Engine fuses of Digital Motor Electronics

Fig 3: Identifying Engine Fuses Of Digital Motor Electronics

Courtesy of BMW OF NORTH AMERICA, INC.

Notes on troubleshooting:

If the starter motor cranks the engine during the starting sequence but the engine fails to fire, then:

Check engine fuses
If fuses are blown, replace them completely with fuse holder
Find out why fuses have blown

Continue troubleshooting as per DIS instructions.