Main relay, engine management system
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Main relay, engine management system
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When +15 from the ignition switch is applied to the engine control unit, the main relay will be activated and +30 is supplied from main relay pin 87 via fuse 14 to the following components.
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A/C compressor relay (156)
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Charge air control valve (179)
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Mass air flow sensor (205)
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EGR solenoid valve (606)
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V6 diesel control module (655)
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Power stage, injectors (656)
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When the ignition key is turned to OFF, +15 will disappear from pin 24 and the running-on function in the engine control module will start. The control module will turn off the main relay, cutting the power to the control module, only when the running-on function has completed. This will take about 40 seconds after the ignition key has been turned to OFF. Diagnostic communication will work after the running-on until communication with Tech 2 has ceased.
If a fault occurs in the main relay circuit, one of the following DTCs can be generated:
P1652 Main relay. Short to ground.
P1653 Main relay. Short to B+.
System reaction to a fault
