2004 Honda Civic Owner's Manual - Page 218

State Emissions Testing Testing of Readiness Codes If you take your vehicle for a state emissions test shortly after the battery has been disconnected or gone dead, it may not pass the test. This is because of certain ''readiness codes'' that must be set in the onboard diagnostics for the emissions systems. These codes are erased when the battery is disconnected, and set again only after several days of driving under a variety of conditions. If the testing facility determines that the readiness codes are not set, you will be requested to return at a later date to complete the test. If you must get the vehicle re-tested within the next two or three days, you can condition the vehicle for re-testing by doing the following. Make sure the gas tank is nearly, but not completely, full (around 3/4). Make sure the vehicle has been parked with the engine off for 8 hours or more. Make sure the ambient temperature is between 20° and 95°F. Without touching the accelerator pedal, start the engine, and let it idle for 20 seconds. Keep the vehicle in Park (automatic transmission) or Neutral (manual transmission). Increase the engine speed to 2,000 rpm and hold it there until the temperature gauge rises to at least 1/4 of the scale (approximately 3 minutes). CONTINUED Technical Information 215