&quot;A third warning indicates when 515 miles are left and also warns that the DEF tank needs re-filling or <i>the vehicle will not be able re-start when the distance countdown reaches 0</i>.&quot;<p>Wow.<p>&quot;The engine will only start again when the DEF tank is re-filled.&quot;<p>And thus the the &quot;faulty DEF sensor&quot; malfunction is introduced into our car fault lexicon.