Boost pressure on a 603 is 0.9 atm or 13.2 psi or so, higher than on the older 617 engine. I suspect the switch closes at 15 psi or so, but I don't know for sure.

The turbo will cheerfully produce 20 psi if the wastegate sticks closed.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!