GM Service Manual Online
For 1990-2009 cars only
  1. When you install power seat adjusters, verify that both of the adjusters are parallel and in phase with each other. Both of the adjusters reach their maximum horizontal or vertical travel in a given direction at the same time if the adjusters are in phase with each other.
  2. If the adjusters are out of phase, perform the following adjustment:
  3. 2.1. Horizontal Travel
             2.1.1. Operate the seat control switch until 1 adjuster reaches the full-forward position.
             2.1.2. Detach the horizontal drive cable from the adjuster which has reached the full forward position.
             2.1.3. Operate the seat forward until the other adjuster reaches the full-forward position.
             2.1.4. Connect the horizontal drive cable.
             2.1.5. Operate the seat in order to verify for correct horizontal travel.
    2.2. Front or Rear Vertical Travel
             2.2.1. Operate the seat control switch until 1 adjuster has reached the fully-raised position at both the front and the rear vertical travel limits.
             2.2.2. Disconnect both of the vertical drive cables from the adjuster which has reached the fully-raised position.
             2.2.3. Operate the seat control switch until the other adjuster reaches the fully-raised position at both the front and the rear vertical travel limits.
             2.2.4. Connect the previously removed front and rear vertical drive cables.
             2.2.5. Test the vertical travel by operating the adjusters through 1 or 2 complete cycles.
             2.2.6. Repeat this procedure as required if the adjusters are still out of phase after the test cycle.