12 63 520 Replacing master relay (M51, M52, M62): Notes

Switch off ignition.

Fold open locking bracket (1).

Remove rubber gasket (2).

Fig 1: Removing Rubber Gasket

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Remove retaining clip (3).

Pull filter housing (4) upwards to remove.

Fig 2: Removing Retaining Clip From Filter Housing

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Unscrew bolts (1).

Fig 3: Identifying Filter Housing Bolts

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M52, M62:

Fig 4: Identifying Master Relay In Digital Motor Electronics

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Notes on troubleshooting:

If the starter cranks the engine during the starting sequence but the engine fails to fire, check the engine fuses and, if necessary, replace them entirely along with the fuse holder.
Search for cause of melting of fuses.

M51:

Remove master relay (1) from Digital Diesel Electronics.