As a note, the 5 minute timing may also indicate an issue with the speed sensor. Without the input from that (or PAS) to tell it it's still in use and moving, it turns off automatically, though you should still be able to turn it back on normally (it'll just shut off again in 5 more minutes).
Some of them have an auto-off setting in the LCD you can disable, but I don't know which one it is. (should be in various threads around ES).