[Skimmer]

There are two ways.

Either change the health of the vehicle to a extrem high value

pawn Код:

SetVehicleHealth(vehicleid, 1000000);

https://sampwiki.blast.hk/wiki/SetVehicleHealth

or update vehicle health in OnPlayerUpdate callback.

pawn Код:

public OnPlayerUpdate(playerid)
{
    new vehicleId = GetPlayerVehicleID(playerid);
    if(vehicleId == YOUR_POLICE_VEHICLE ID)
    {
        SetVehicleHealth(vehicleId, 1000);
    }
}