Code 53 and/or 73
WARNING: This page is about a different car, the 1988 Buick Riviera and 1988 Buick Reatta. However, it is still accessible from the selected car via links, so may be relevant.
Go to Chart A11 If no trouble is found while performing tests on Chart A11, do not go to chart F Instead go to Chart G Solenoid Valves. Perform solenoid valve test for rear valves. If no trouble is found, replace ECBM.