The penalty will differ from state to state for an inspection sticker that is expired or past the extended time to get the car to pass the inspection.

In general though if you have passed the extension time to get your car to pass inspection and it has either failed or you have not taken the car in for inspection and thus do not have a current inspection sticker you will be give a citation. In most states the penalty will then be a fine though there may be states with stiffer penalties such as suspension of your registration until your car is inspected and found roadworthy.

To find out what your specific state's penalties are for this violation contact your local Department of Motor Vehicles.