UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                  SCHEDULE 13D

                    Under the Securities Exchange Act of 1934
                               (Amendment No. 2)*

                                    ABB LTD.
                                    --------
                                (Name of Issuer)

                    Registered Shares, CHF 2.50 nominal value
                    -----------------------------------------
                         (Title of Class of Securities)

                                  CH0012221716
                             -----------------------
                                 (CUSIP Number)

                               James E. Kaye, Esq.
                       Akin Gump Strauss Hauer & Feld LLP
                               590 Madison Avenue
                            New York, New York 10022
                                 (212) 872-1000
                --------------------------------------------------
                  (Name, Address and Telephone Number of Person
                Authorized to Receive Notices and Communications)

                               December 31, 2005
                      -------------------------------------
                      (Date of Event which Requires Filing
                               of this Statement)

If the filing person has previously  filed a statement on Schedule 13G to report
the  acquisition  that is the subject of this  Schedule  13D, and is filing this
schedule because of ss.ss.240.13d-1(e),  240.13d-1(f) or 240.13d-1(g), check the
following box [ ].

Note:  Schedules  filed in paper format shall include a signed original and five
copies of the schedule,  including all exhibits. See Rule ss.240.13d-7 for other
parties to whom copies are to be sent.

*The  remainder of this cover page shall be filled out for a reporting  person's
initial filing on this form with respect to the subject class of securities, and
for  any  subsequent   amendment   containing   information  which  would  alter
disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the  Securities  Exchange  Act of
1934 ("Act") or otherwise  subject to the liabilities of that section of the Act
but  shall be  subject  to all other  provisions  of the Act  (however,  see the
Notes).

                         Continued on following page(s)
                                Page 1 of 7 Pages





                                  SCHEDULE 13D

CUSIP No. CH0012221716                                         Page 2 of 7 Pages


1        Names of Reporting Persons
             I.R.S. Identification Nos. of above persons (entities only)

                  INVESTOR AKTIEBOLAG

2        Check the Appropriate Box If a Member of a Group (See Instructions)
                                     a. [ ]
                                     b. [x]

3        SEC Use Only

4        Source of Funds (See Instructions)

                  Not Applicable

5        Check Box If Disclosure of Legal  Proceedings Is Required Pursuant to
         Items 2(d) or 2(e)
             [  ]

6        Citizenship or Place of Organization

                  Sweden

         Number of            7          Sole Voting Power
           Shares                              166,330,142
        Beneficially
          Owned By            8         Shared Voting Power
            Each                               0
         Reporting
           Person             9         Sole Dispositive Power
            With                               166,330,142

                              10        Shared Dispositive Power
                                               0

11       Aggregate Amount Beneficially Owned by Each Reporting Person

                  166,330,142

12       Check Box If the Aggregate Amount in Row (11) Excludes Certain Shares
         (See Instructions)

                  [ ]

13       Percent of Class Represented By Amount in Row (11)

                  8.2%

14       Type of Reporting Person (See Instructions)

                  OO





                                                               Page 3 of 7 Pages


                  This  Amendment  No. 2 to Schedule  13D relates to  Registered
Shares,  CHF  2.50  nominal  value  (the  "Shares"),   of  ABB  Ltd,  a  company
incorporated in Switzerland (the "Issuer").  This Amendment No. 2 supplementally
amends the initial  statement on Schedule  13D,  dated  November  22, 2002,  and
Amendment  No. 1,  dated  March 4, 2005  (together,  the  "Initial  Statement").
Investor  AB (as  defined  below)  is  filing  this  Amendment  No. 2 to  update
information regarding Investor AB (as defined below). Capitalized terms used but
not  defined  herein  shall have the  meanings  ascribed  to them in the Initial
Statement.

Item 2.           Identity and Background.

                  This   Statement   is  being   filed  on  behalf  of  Investor
Aktiebolag,  a limited liability company  incorporated  under the laws of Sweden
("Investor AB," defined as "Buyer" in the Initial Statement).

                  The address of the principal business and the principal office
of  Investor  AB  is  Arsenalgatan  8C,  S-103  32  Stockholm,  Sweden.  Updated
information  concerning  the  identity  and  background  of  the  directors  and
executive  officers  of  Investor  AB is set forth in Annex A  hereto,  which is
incorporated by reference in response to this Item 2.

                  Investor  AB  is  a  Swedish  diversified  industrial  holding
company.  Investor AB's founders and principal  shareholders  are the Wallenberg
foundations,  whose holdings, as of January 31, 2006, represented  approximately
46.9% of the votes and 21.98% of the share capital of Investor AB.

                  During the last five years, neither Investor AB, nor any other
person controlling Investor AB nor, to the best of Investor AB's knowledge,  any
of the persons  listed in Annex A attached  hereto,  (i) has been convicted in a
criminal  proceeding  (excluding traffic violations or similar  misdemeanors) or
(ii) has been a party to a civil proceeding of a judicial or administrative body
of competent  jurisdiction  and as a result of such proceeding was or is subject
to a  judgment,  decree  or final  order  enjoining  future  violations  of,  or
prohibiting or mandating activities subject to, federal or state securities laws
or finding any violation with respect to such laws.

Item 5.           Interest in Securities of the Issuer.

                  (a) The  percentages  set forth herein are  calculated  on the
basis of the Issuer having,  to Investor AB's  knowledge,  2,028,404,505  Shares
outstanding  as of the date  hereof.  Investor AB, for the purpose of Rule 13d-3
promulgated  under the  Securities  Exchange Act of 1934 (the  "Exchange  Act"),
beneficially owns approximately 166,330,142 Shares,  representing  approximately
8.2% of the outstanding Shares of the Issuer.

                  Sune Carlsson, for the purpose of Rule 13d-3 promulgated under
the Exchange Act and to Investor AB's knowledge, beneficially owns approximately
27,185  Shares,  representing  less than 0.1% of the  outstanding  shares of the
Issuer.

                  Bjorn  Svedberg,  for the  purpose of Rule  13d-3  promulgated
under  the  Exchange  Act and to  Investor  AB's  knowledge,  beneficially  owns
approximately  15,000  Shares,  representing  less than 0.1% of the  outstanding
shares of the Issuer.





                                                               Page 4 of 7 Pages


                  Jacob  Wallenberg,  for the purpose of Rule 13d-3  promulgated
under  the  Exchange  Act and to  Investor  AB's  knowledge,  beneficially  owns
approximately  137,046  Shares,  representing  less than 0.1% of the outstanding
shares of the Issuer.

                  Peter  Wallenberg,  for the purpose of Rule 13d-3  promulgated
under  the  Exchange  Act and to  Investor  AB's  knowledge,  beneficially  owns
approximately  43,494  Shares  representing  less than  0.1% of the  outstanding
shares of the Issuer.

                  Except as set forth in this Item 5(a),  none of  Investor  AB,
and, to its knowledge, any persons named in Annex A hereto beneficially owns any
Shares.

                  (b)  Investor  AB has sole  power to vote  and to  dispose  of
166,330,142 Shares.

                  To  Investor  AB's  knowledge,  each of Sune  Carlsson,  Bjorn
Svedberg,  Jacob  Wallenberg and Peter  Wallenberg has sole power to vote and to
dispose of his respective Shares.

                  (c) There have been no transactions with respect to the Shares
since November 1, 2005 (60 days prior to the date hereof) by Investor AB.

                  (d) Not applicable.

                  (e) Not applicable.





                                                               Page 5 of 7 Pages

                                   SIGNATURES


     After reasonable  inquiry and to the best of my knowledge and belief,  each
of the undersigned certifies that the information set forth in this Statement is
true, complete and correct.

Date:     February 17, 2006              INVESTOR AB


                                         By: /s/ Adine Grate Axen
                                             -----------------------------------
                                             Adine Grate Axen
                                             Managing Director





                                                               Page 6 of 7 Pages

                                     ANNEX A

                 Directors and Executive Officers of Investor AB

     The  name,  business  address,   title,  present  principal  occupation  or
employment of each of the  directors  and executive  officers of Investor AB are
set forth below.  If no business  address is given,  the director's or officer's
business  address  is  Arsenalsgatan  8C,  S-103 32  Stockholm,  Sweden.  Unless
otherwise  indicated,  each occupation set forth opposite an  individual's  name
refers to Investor AB.  Unless  otherwise  indicated  below,  all of the persons
listed below are citizens of Sweden.

                                 Present Principal Occupation Including Name and
   Name and Business Address                  Address of Employer
-----------------------------    -----------------------------------------------

Directors

Jacob Wallenberg.................       Chairman.
                                        Vice  Chairman of Atlas Copco AB, SAS AB
                                        and  Skandinaviska  Enskilda Banken SEB.
                                        Director of ABB Ltd., the Knut and Alice
                                        Wallenberg    Foundation,    the   Nobel
                                        Foundation and W Capital Management.

Anders Scharp....................       Vice Chairman.
                                        Chairman of Ph.  Nederman & Co., Saab AB
                                        and AB SKF.

Hakan Mogren.....................       Member of the Board.
                                        Non-Executive     Vice    Chairman    of
                                        AstraZeneca  PLC and  Vice  Chairman  of
                                        Gambro  AB.  Director  of Group  Danone,
                                        Norsk Hydro ASA, Remy  Cointreau SA, The
                                        Marianne    and    Marcus     Wallenberg
                                        Foundation   and  the   Swedish-American
                                        Foundation.  Member of the Royal Swedish
                                        Academy of Engineering Sciences (IVA).

Sune Carlsson....................       Member of the Board.
                                        Chairman  of  Atlas   Copco  AB.   Vice
                                        Chairman  of  Scania  AB.   Director  of
                                        Autoliv Inc., and Picanol NV

Bjorn Svedberg...................       Member of the Board.
                                        Chairman  Nefab  AB.  Director  of  Hi3G
                                        Access   AB  and  the  Knut  and   Alice
                                        Wallenberg  Foundation.  Member  of  the
                                        Royal  Swedish  Academy  of  Engineering
                                        Sciences (IVA).






                                                               Page 7 of 7 Pages


Sirkka Hamalainen................       Member of the Board.
                                        Vice   Chairman  of  KONE   Corporation.
                                        Director of HKKK Holding, the Foundation
                                        for Economic  Education and  SanomaWSOY.
                                        Citizen of Finland.

Ulla
Litzen...........................       Member of the Board.
                                        Director of Atlas Copco AB,  Boliden AB,
                                        Karo Bio AB, AB SKF and Posten AB.

O. Griffith
Sexton...........................       Member of the Board.
                                        Director of Morgan  Stanley.  Citizen of
                                        the United States.

Peter
Wallenberg.......................       Honorary Chairman.
                                        Chairman   of   the   Knut   and   Alice
                                        Wallenberg   Foundation   and   Honorary
                                        Chairman of Atlas Copco AB.

                                        Present Principal Occupation Including
   Name and Business Address                 Name and Address of Employer
-------------------------------------   ----------------------------------------

Executive Officers
(Who Are Not Directors)
Borje Ekholm................... President and Chief Executive Officer
Lars Wedenborn................. Executive Vice President
Henry E. Gooss................. Managing Director.  Citizen of the United States
Adine Grate Axen............... Managing Director
Johan Forssell................. Managing Director
Lennart Johansson.............. Managing Director