The following link explains how to troubleshoot the "F06" error code:http://www.fixya.com/support/r714929-f06_error_whirlpool_duet_kenmore_elite
The first step in toubleshooting this problem is to check all the connector plugs between the Drive Motor, MCU and CCU. Check for loose connections and then unplug each connector and plug them back in (one at a time) to ensure they are snug and making good contact.
NOTE: You only need to check the connectors that affect the drive motor and MCU circuitry.
If the tachometer is determined to be the cause of the problem, it is part of the MCU. The MCU is not serviceable and will require replacement. Next, check the motor windings to ensure they are reading the proper resistance. Followed by continuity checks of all the interconnecting wiring between the drive motor, MCU and CCU. For more in depth troubleshooting tips refer to your technical data sheet that came with the washer. It is located inside the washer behind the lower toe panel. You will need to locate and remove the screws under the bottom front edge of the toe panel. Once removed, the panel will drop down, then come off. If the tech sheet isn't located directly behind the panel, it will be affixed to one of the interior cabinet walls. The tech sheet includes all error codes, test points, dianostic procedures and helpful illustrations to assist in troubleshooting and repair of your washer.
If you have questions, or require additional assistance, please let me know.
NOTE: For better access to the toe panel screws, you can prop the two front feet of the washer up. (A 2x4 works real well for this).