Basic mode was a mode activated by the Eleventh Doctor, in order to help Clara Oswald bond with the TARDIS. When in basic mode, the TARDIS was easier to fly due to its shield oscillators being deactivated.
During this test drive, a nearby salvage ship was able to capture the TARDIS with a magnetic hobble-field. With the shields down, their magno-grab broke the TARDIS, causing the ship's engine to explode. (TV: Journey to the Centre of the TARDIS)