Why do diesels have vacuum pumps? Well, not all diesels do have vacuum pumps but the ones that do generally have the pumps to provide vacuum to operate a myriad of control functions and accessories. Vacuum would seem to have been considered more reliable than electronics, etc. in engineering some vehicles from the not to distant past. MB liked to use vacuum for brakes, transmission control, emissions control, locks, ECC functions and shutting the engine off. Other manufacturers have used vacuum for the above stuff plus wipers, headlight doors, etc. RT

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