My 2001 cadillac deville check engine light is on and the code is p0471?

The first step is understanding why the check engine light comes on. It is connected to the on-board computer and is only set when the on-board computer detects a fault in engine driveability or performance, transmission control system or transmission, or the emissions system, and a fault code is set and stored in the computer. Faults that can set the check engine light can range from a vaccuum leak, engine mis-fire, low engine compression, faulty sensor such as O2 sensor or other engine sensor, hydraulic pressure loss in transmission, transmission shift solenoid, open/short in wiring harness, emission evaporative system leak, or one of over 300 reasons. And not every fault that is set will have outward symptoms.