Possible Causes

WARNING: This page is about a different car, the 2006 Mercury Milan, 2006 Lincoln Zephyr, and 2006 Ford Fusion. However, it is still accessible from the selected car via links, so may be relevant.

A driver differential temperature fault can be caused by:

Wiring, terminals or connectors.
Restricted cushion or backrest TED filter.
Crushed or restricted cushion or backrest foam pad.
Crushed or restricted cushion or backrest climate controlled seat manifold.
A faulted cushion or backrest TED assembly.
A faulted DCSM.