how to fix garmin nuvi 1340??

Only a guess as I've done it, then might be the only idiot that has. once started look at volume see if its set to mute or for some reason you may have turned down sound volume.
If the warranty is out and its under six yrs old and that it is a fault it should be repaired FREE under the sale of goods act (UK only.) as not of merchantable quality through manufacturing fault. Try it its worth a go.
Incidentally my nuvi 250 tells lies does yours?

Also Copy and paste your question in to Navigation below Music just re-type title box. Then look out for replies in both as this section is for mainly TV & Sat dish problems..

Bob
September 2012