mapAsync.js

// mapAsync
function mapAsync(arr, process, callback) {
    var output = [];

    arr.forEach((element) => {
        process(element, (err, data) => {
            if (err) {
                throw err;
            } 

            output.push(data);

            if (output.length === arr.length) {
                callback(output);
            }
        });
    });
}

function yourCode() {
    mapAsync(vehicles, (vehicle, callback) => {
        VehicleModel.findOne({_id: ownedVehicle.vehicleId}, (err, vehicle) => {
            if (err) callback(err);

            console.log(vehicle);

            callback(null, {
                year: vehicle.year,
                make: vehicle.make,
                model: vehicle.model,
            });
        });        
    }, (output) => {
        // This is called when all the shit is computered
        res.json(output);
    });
}