Why wont my third row seat fold all the way down?

The second row is folded by first pulling up the rear of the seat cushion and folding up 'til it's behind the back of the front seat. Then the back of the seat folds down where the seat cushion was.

The third row seats have several levers that are numbered in the sequence they are to be operated. First fold the seat back down on to the cushion and then flip the whole seat up 'til it's vertical and latched.

This is described in the Owner's manual if you can find one.

Your missing something's G-404 has nothing to do with it !
Seats - Third Row
The third row seat:

• is three-passenger seat.
• a 60/40 bench seat.
• folds down for more cargo area.
• has optional power fold down seats.

Third Row Power-Fold Seat
CAUTION: To prevent possible damage to the third row seat or the safety belts, make sure that the safety belts are not fastened when moving the seat to the load floor position.
CAUTION: Make sure that no objects such as books, purses or briefcases are on the floor in front of the third row seats or on the seat cushion before lowering the backrest(s).
The third row power-fold seat consists of the following electrical components:

• right third row seat relay.
• left third row seat relay.
• right power-fold seat motor.
• left power-fold seat motor.
• right front third row seat switch (if equipped).
• left front third row seat switch (if equipped).
• right rear third row seat switch.
• left rear third row seat switch.

For the third row power-fold seat to operate, a shared ground is supplied by the body security module (BSM) to both of the power-fold seat relays, enabling the seats to then be moved by pressing one of the third row power-fold seat switches. The third row power-fold seat operates only when the vehicle is in PARK and the liftgate glass, liftgate door or any entry door must be open.
The third row power-fold seat motors transfer movement to a drive gear assembly to raise and lower the seat backrest. The power-fold seat motors rotate a short drive cable which is connected to the drive gear assembly.
The relay's are located in Aux. relay box #2

The seats shouldn't lock, its probably bound up. If you don't want to spend big bucks at the dealership, you might stop by a local automotive uphostery shop. Those guys work with seats every day.

Probably, but you could try on-line or at a Chevrolet dealer for a owners/service manual.

mechanism lower seat driven by electric motor is broken.

look for a broken cable

Call the dealership and ask them how to reset the electronic on your Ford Expedition after changing the battery. Anything else is happen? Maybe like the radio wont turn on, hit the turn signals and the windshield wiper turn on. ***** things happen after replace the battery. I know what it is, it the darn wigits. GB you....stewbison

If you are talking about the third row seat, the first step is to fold the seat down. Pull the lever behind the passenger side of the third row seat and fold the seat down. Then, from the cargo area, raise the bar located directly behind the third row seat and lift the seat forward. The seat should now be detached from the car and can be removed. When you reinstall the seat, be sure to secure the seat properly so passengers do not get injured in a sudden vehicle maneuver. This should help you to fix your problem. Contact me at FixYa if you have any further questions.

Nope. 3rd row was never offered with a trailblazer even the EXT modles.