I cleared the code and it reset after a couple of days. This was during very easy driving at less than 50 MPH. As the car is never pushed very much, I wonder if a pressure sensor might be failing, or the wastegate may be sticking? After all, it is 12 years and 168000 miles old.

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Providing a home for these cars:
1951 Buick Special De Luxe
1977 Rolls-Royce Silver Wraith II
1970 Rolls-Royce Silver Shadow
1986 Mercedes-Benz 420 SEL
2005 Mercedes-Benz E 320 CDI
2012 GMC Sierra 1500 4X4
1927 Pierce-Arrow Series 80
1931 Pierce-Arrow Series 43
1926 Ford Model T coupe