The sensor and switchover valve cuts the boost signal to the alda if an overboost situation should occur. Generally there are 2 incidents where this could occur, 1 your wastegate hose breaks, and you do not notice it in time. 2 your wastegate seizes closed.

These are very rare incidents, and I generally replace the wastegate hose every few years.

Your call.

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1984 Euro 300SDC, (4spd standard)
1986 Toyota Landcruiser Diesel HJ60 5spd X2

Gone but not forgotten (some sold, some stripped)
1983 300 SD, 1985 300 SD, 1983 240D, 1986 300 SDL, 1985 300 SDL, 1983 300 D, 1984 300 D, 1985 300SD, 1987 300 SDL, 1983 300 SD, 1985 300 TD Euro, 1983 380SEC, 1990 300 D, 1987 300D, 1982 300D, 1982 300D, 1994 E420, 1987 300 TD, 1987 300 D, 1984 300 D