Abstract: A cylinder of a diesel engine that is used to drive a vehicle is decompressed by opening its exhaust valve. When the engine brake of the vehicle is applied a first high pressure fluid is applied to one side of a shuttle valve moving it in one direction and applying the high pressure to open the exhaust valve. The driver may also decompress the engine, during starting of the engine, for example, by throwing a switch on the vehicle dashboard that starts a fluid pump that applies high pressure fluid to drive the shuttle valve in another direction and to open the exhaust valves. The shuttle valve isolates the two sources of high pressure fluid.