Misfire Affecting Emission Levels

If the engine control module (ECM) detects a certain number of misfires during 1000 engine revolutions, this is interpreted as misfiring which affects emissions. If misfiring is detected in the first 1000 engine revolutions a diagnostic trouble code (DTC) is stored and the malfunction indicator lamp (MIL) lights. However, if misfiring is detected after the first 1000 engine revolutions, four misfires need to be detected before a diagnostic trouble code (DTC) is stored.