After step chalks are placed under a vehicle, what must occur next?

After placing step chalks under a vehicle, the immediate action that should be taken is to secure the vehicle. This is crucial because step chalks are designed to prevent the vehicle from rolling when it is being serviced or investigated, ensuring the safety of personnel working around it.

To secure the vehicle effectively, the following actions could be implemented: putting the vehicle in park, setting the parking brake, or using additional chocks, especially if the vehicle is on an incline. Deflating the tires could lead to instability and potential hazards; therefore, it is not a recommended or safe practice. Moving the vehicle or calling for backup does not directly relate to the immediate safety measures required after placing step chalks. Thus, securing the vehicle is the correct next step to maintain a safe working environment.