Here are your parts
Replacement parts for FRIGIDAIRE GLEH1642DS0 Frigidaire/laundry Center | AppliancePartsPros.com

Here is the tech sheet
http://manuals.frigidaire.com/prodinfo_pdf/Webster/134392800_134422900.pdf

Have you cleaned the moisture sensor bars?
Item 57 in Section 2, click on the picture of the part for a better view.

The way it works is that the moisture from the clothes allows a small current to flow between the bars. The board then holds the timer off. When the moisture evaporates (clothes are dry) the current stops and the board senses this and advances the timer to off.
Any dirt/residue between the bars will also allow a current so the unit thinks the clothes are still wet.

Clean between them with a damp cloth, drying it thoroughly.
If that does nothing try electronics contact cleaner or isopropyl alcohol.
Just be sure to let the solvent dissipate before trying.

If that does nothing you will need a meter.
Unplug the unit.
Set your meter to a high ohms scale (200 Kohms or higher)
Undo P1 and P2 at the sensor board and measure across them (the sensor bars).
They should be infinite ohms (open).
Also check from each wire to the machine frame, They should also be infinite ohms.
If not you have a problem with the sensor. Could be a wire is touching the units frame or there is crud at the back of the sensor bars.

If all are open then odds are that the sensor board is shot.