No. Keep cars, RVs, trailers and other heavy vehicles off a conventional septic drainfield, even for temporary parking. Their weight can compact the soil and damage buried pipes. The field relies on suitable soil conditions to accept and treat wastewater, so an area that looks like firm lawn should not be treated as an extra parking space.
Use the system drawing to identify the drainfield before arranging guest parking, deliveries or building work, and show the area to anyone bringing a vehicle onto the property. Choose a route that avoids it. If a vehicle has crossed the field and you notice ruts, exposed components or new drainage problems, describe what happened when requesting a septic inspection. There is no reliable vehicle-weight limit that can be given without knowing the system’s design and condition.