There is likely no serious problem with the smoke unit. Here are four common issues to check with your smoke unit. 1. Too much or too little smoke fluid was added. You should add 3-4 drops of smoke fluid. If you added more than that, you should runt he unit at high speed for several minutes to burn off excess oil. 2. Make sure the slide switch under the front smoke box cover is in the ON position. The switch is located beneath the cab on the underside of the chassis on some models. 3. Make sure the F7 function is active on your DCC control system. It is possible to accidentally toggle F7 to OFF when you are operating your model. 4. There could be an air bubble clogging the smoke fluid reservoir. Gently blow into the smoke stack of the model - this will clear the bubble.