Get in the service manual, go to Chapter 25 "Emissions Control", then go to "Evaporative Emissions" in that chapter.
IGNORE the parts on the EGR and crankcase ventilation. Concentrate on the EVAP diagram, this is the system that is failing the test, if, indeed, it is really failing (keep reading).

KEEP IN MIND that the system may be just fine, and what you have is a flaky sensor or corroded connector on the sensor, this got me back in about 2010 with my first Roadster. The connector is in the top of the tank and I'd allowed water to get in the connector causing corrosion and setting off a P0453. With what you have, the sensor is indicating a large leak, which means the pressure indication falls too quickly once the system pressurizes. But again, the ECU may interpret unstable readings as a gross leak -unstable due to a poor connection or a failing sensor; you may or may not have a big leak. My BOSCH 1100 reader cannot see the sensor's output and besides, you must meet the criteria for the ECU to perform the test. HOWEVER: You could use a voltmeter to watch the reading and see if it jumps around a lot, it SHOULD be very stable both when the test is not running and when it is running. (Either around .9 volts or nearly 4.5 volts if I remember correctly.) If it is moving around a lot, the connection to the sensor is bad, the sensor is bad, or the supply voltage from the ECU is unstable (probably due to a corroded connector between the ECU and the sensor).