[clarencecuzz]

pawn Код:

CMD:engine(playerid, params[])
{
    new engine, lights, alarm, doors, bonnet, boot, objective, vehicleid, string[128];
    if(GetPlayerState(playerid) != PLAYER_STATE_DRIVER) return SendClientMessage(playerid, COLOR_GREY, "You are not driving a vehicle.");
    vehicleid = GetVehicleModel(GetPlayerVehicleID(playerid));
    if(vehicleid == 509 || vehicleid == 481 || vehicleid == 510) return SendClientMessage(playerid, -1, "Bicycles have no engine.");
    vehicleid = GetPlayerVehicleID(playerid);
    GetVehicleParamsEx(vehicleid, engine, lights, alarm, doors, bonnet, boot, objective);
    if(!engine)
    {
        SetVehicleParamsEx(vehicleid, 1, lights, alarm, doors, bonnet, boot, objective);
    }
    else
    {
        SetVehicleParamsEx(vehicleid, 0, lights, alarm, doors, bonnet, boot, objective);
    }
    return 1;
}

You used vehicleid before you defined it.