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Main relay, engine management system

Main relay, engine management system



The main relay is activated by +30 current. The following components are supplied with current from pin 87 of the main relay via fuse 14:


• Control module and diesel pump, PSG 16 (595)

• Control module, glow plugs (596)

• Solenoid valve, charge air (179a)

• Solenoid valve, swirl throttle (403)


When the ignition is turned OFF, +15 disappears from pin 16 and the time delay starts in the engine control module. The control module only switches off the main relay, thus becoming deenergized, once the time delay has run out. This time delay lasts about one minute from the ignition being switched OFF. Diagnostic communication also works during this time delay period.

Diagnostics

If a fault arises in the main relay circuit, one of the following DTCs can be generated:

P1652 Main relay. Late voltage drop.

P1653 Main relay. No power to control module.