EXHIBIT 99.6

      TRIPARTY CONTINGENT ASSIGNMENT AGREEMENT dated as of December 9, 2004 (the
"Agreement"), among Capital Auto Receivables Asset Trust 2004-2 (the "Trust"),
General Motors Acceptance Corporation ("GMAC"), and Credit Suisse First Boston
International ("Primary Swap Counterparty").

      WHEREAS, the Trust and the Primary Swap Counterparty have entered into the
Primary Swap Agreement (hereinafter defined);

      WHEREAS, GMAC and the Primary Swap Counterparty have entered into the
Back-to-Back Swap Agreement (hereinafter defined);

      NOW, THEREFORE, the parties hereto hereby agree as follows:

                                   ARTICLE I

                                   DEFINITIONS

      Section 1.01 The following terms shall have the meanings set forth below:

      "Additional Contingent Counterparty" means a Person with the Requisite
Rating entering into an agreement substantially similar to this Agreement
pursuant to Section 2.02.

      "Assignment Currency" means United States Dollars.

      "Assignment Currency Equivalent" has the same meaning as the term
"Termination Currency Equivalent" as defined in the Primary Swap Agreement.

      "Assignment Date" means the date upon which GMAC receives notice from the
Trust of the occurrence of a Designated Event, or if such date is not a Business
Day, the next succeeding Business Day.

      "Back-to-Back Swap Agreement" means ISDA Interest Rate and Currency
Exchange Agreement (including the Schedule thereto), dated May 26, 1992 between
GMAC and the Primary Swap Counterparty, as successor to Credit Suisse Financial
Products, and each Back-to-Back Confirmation.

      "Back-to-Back Confirmation" means the Confirmation evidencing the terms of
an interest rate swap relating to the Class A-1b Notes between GMAC and the
Primary Swap Counterparty, in effect on the Closing Date, which has been or will
be entered into pursuant to the Back-to-Back Swap Agreement.

      "Back-to-Back Swap Transaction" means each transaction described in a
Back-to-Back Confirmation.

      "Closing Date" means December 9, 2004.



      "Delinquent Payments" means any payments owed to the Trust as a result of
liabilities, obligations and duties of the Primary Swap Counterparty pursuant to
the Primary Swap Agreement accruing prior to the Assignment Date that have not
been made by the Primary Swap Counterparty.

      A "Designated Event" shall occur (a) if one or more Events of Default
occurs under the Primary Swap Agreement with the Primary Swap Counterparty as
the Defaulting Party and the Trust notifies the Primary Swap Counterparty that
it is declaring a Designated Event to have occurred, (b) upon the occurrence of
any applicable Termination Event under the Primary Swap Agreement in which the
Primary Swap Counterparty is an Affected Party, if no transfer is effected under
Section 6(b)(ii) of the Primary Swap Agreement with respect to such event and an
assignment pursuant to Section 2.01 would not result in the occurrence of an
independent Termination Event under the resulting Fallback Swap Agreement, (c)
upon the occurrence of a "Credit Downgrade" as described in any Primary
Confirmation, if no appropriate arrangements pursuant to such Primary
Confirmation's credit downgrade provisions are made within thirty (30) days of
receipt of notice of such reduction unless, within thirty (30) days after such
reduction, the applicable Rating Agency has reconfirmed the rating of the Notes
that was in effect immediately prior to such reduction with respect to such
"Credit Downgrade" event, and an assignment pursuant to Section 2.01 would
result in the non-occurrence of such event as it pertains to the Primary Swap
Counterparty or (d) if the Trust receives a notice from the Primary Swap
Counterparty pursuant to the provisions of Section 2.03 herein.

      "Fallback Swap Agreement" means the ISDA Master Agreement (including the
Schedule thereto), dated as the date hereof, between GMAC and the Trust, and
each Fallback Confirmation.

      "Fallback Confirmation" means the Confirmation between GMAC and the Trust,
documented under the Fallback Swap Agreement relating to the Class A-1b Notes,
evidencing the terms of an interest rate swap, assigned to GMAC by the Primary
Swap Counterparty in accordance with section 2.01 hereof following the
occurrence of a Designated Event.

      "Fallback Swap Transaction" means each transaction resulting from the
assignment of a transaction under the Primary Swap Agreement upon the occurrence
of a Designated Event, the terms of which are set forth in a Fallback
Confirmation.

      "Joint Probability" has the meaning given in the Primary Confirmation.

      "Moody's" means Moody's Investors Service and any successor.

      "Person" means any legal person, including any individual, corporation,
partnership, joint venture, association, limited liability company, joint stock
company, trust, unincorporated organization or government or any agency or
political subdivision thereof.

      "Primary Swap Agreement" means the ISDA Master Agreement (including the
Schedule thereto), dated as the date hereof, between the Primary Swap
Counterparty and the Trust, and each Primary Confirmation.

                                       2


      "Primary Confirmation" means the Confirmation evidencing the terms of an
interest rate swap relating to the Class A-1b Notes, between the Primary Swap
Counterparty and the Trust, in effect on the Closing Date, which has been or
will be entered into pursuant to the ISDA Master Agreement (including the
Schedule thereto), dated as of the date hereof, between the Primary Swap
Counterparty and the Trust.

      "Primary Swap Transaction" means each transaction described in a Primary
Confirmation.

      "Requisite Rating" means a long-term, unsecured and unsubordinated debt
rating from S&P or Moody's which, when considered together with the long-term,
unsecured and unsubordinated debt rating of GMAC, would result in a Joint
Probability of at least AA- in the case of S&P and, Aa3 in the case of Moody's,
in each case so long as the Notes are rated by such Person.

      "Seller" means the Person executing the Trust Sale and Servicing Agreement
as the Seller, or its successor in interest pursuant to Section 3.03 of the
Trust Sale and Servicing Agreement.

      "Settlement Amount" shall mean the amount determined as such under the
Primary Swap Agreement, except that any reference to the term "Termination" or
"Terminated" therein is deemed to be "Assignment and "Assigned" respectively and
reference to "Early Termination Date" shall be a reference to the "Assignment
Date".

      "Servicer" means GMAC or its successor as servicer pursuant to the Trust
Sale and Servicing Agreement.

      "S&P" means Standard and Poor's Ratings Service and any successor.

      "Trust Sale and Servicing Agreement" means the Trust Sale and Servicing
Agreement, dated as of date hereof, between the Seller, the Servicer and the
Trust, as amended and supplemented from time to time.

      "Unpaid Amounts" shall mean the amount determined as such under the
Primary Swap Agreement.

      Section 1.02 Definitions. Capitalized terms used in this Agreement and not
otherwise defined herein shall have the meanings specified for such terms (i) in
the Primary Swap Agreement or the Back-to-Back Swap Agreement, as dictated by
its context or (ii) if not defined therein, in Appendix A to the Trust Sale and
Servicing Agreement, dated as of the date hereof between the Trust, the Seller
and the Servicer (the "Trust Sale and Servicing Agreement"). The rules of
construction specified in Part II of such Appendix A shall apply to this
Agreement.

                                       3


                                   ARTICLE II

                        ASSIGNMENT UPON DESIGNATED EVENT

      Section 2.01 Assignment. In the event that a Designated Event shall have
occurred and is then continuing and the Trust has notified GMAC in writing of
such occurrence and continuance and has provided evidence reasonably
satisfactory to GMAC that a Designated Event has occurred and is then
continuing, each of the following shall automatically occur on the Assignment
Date:

            (a) Each Primary Swap Transaction shall be assigned by the Primary
      Swap Counterparty to GMAC and GMAC shall accede to all of the rights and
      obligations of the Primary Swap Counterparty under each such Primary Swap
      Transaction; provided, however, that upon such assignment, each such
      transaction shall be evidenced by a Fallback Confirmation and shall be
      governed by the terms of the Fallback Swap Agreement (including rights,
      title and interests and liabilities, obligations and duties accruing prior
      to the Assignment Date) and, except as expressly provided in this
      paragraph (a) and paragraph (b) below, on and at all times following the
      Assignment Date, the Primary Swap Agreement and each Primary Swap
      Transaction thereunder shall terminate and neither the Trust nor the
      Primary Swap Counterparty shall have any rights, liabilities, obligations
      or duties thereunder, including, without limitation payment obligations of
      any kind. In connection with the foregoing, in the event that there are
      Delinquent Payments under the Primary Swap Transaction, GMAC shall
      promptly (and in any event no later than the next Business Day) make the
      full amount of such Delinquent Payments to the Trust (but only to the
      extent that GMAC has not made a corresponding payment under the Fallback
      Swap Agreement).

            (b) In connection with the assignment of the Primary Swap Agreement
      to GMAC pursuant to Section 2.01(a) above, a payment (the "Assignment
      Payment") shall be due, either to the Primary Swap Counterparty by GMAC or
      to GMAC by the Primary Swap Counterparty, which payment shall equal (A)
      the sum of the Settlement Amount (as determined by GMAC (on behalf of the
      Trust)) in respect of the Primary Swap Agreement and the Assignment
      Currency Equivalent of the Unpaid Amounts owing to the Trust by the
      Primary Swap Counterparty under the Primary Swap Agreement (without giving
      effect to any Delinquent Payments made by GMAC) less (B) the Assignment
      Currency Equivalent of the Unpaid Amounts owing by the Trust to the
      Primary Swap Counterparty under the Primary Swap Agreement. If that amount
      is a positive number, the Primary Swap Counterparty shall pay it to GMAC;
      if it is a negative number, GMAC shall pay the absolute value of that
      amount to the Primary Swap Counterparty. The amount of the Assignment
      Payment determined as being due as a result of the assignment shall be
      payable within five Business Days following the Assignment Date.

            (c) The Back-to-Back Swap Transaction shall be terminated on and as
      of the Assignment Date . For the purposes thereof, the Assignment Date
      shall be deemed to be an Early Termination Date for the Back-to-Back Swap
      Transaction and the Primary Swap Counterparty shall be deemed to be the
      Affected Party and the payment in respect of the

                                       4


      termination of the Back-to-Back Swap shall be determined in accordance
      with the provisions of Section 6(e)(ii)(1) (the "Back-to-Back Early
      Termination Payment"). If, either GMAC or the Primary Swap Counterparty
      (such party in such capacity, the "Post Assignment Payor") has made
      payments to the other party (such party in such capacity, the "Post
      Assignment Payee") under the Back-to-Back Swap Agreement in respect of
      amounts accruing on or after the Assignment Date, other than the
      Back-to-Back Early Termination Payment, the Post Assignment Payee agrees
      to reimburse the Post Assignment Payor in an amount equal to the full
      amount of any such payments. If, prior to the Assignment Date, GMAC or the
      Primary Swap Counterparty (such party in such capacity, the "Pre
      Assignment Payor") has not made all or any part of the payments required
      to be made by it to the other party (such party in such capacity, the "Pre
      Assignment Payee") under the Back-to-Back Swap Agreement, the Pre
      Assignment Payor agrees to pay, without duplication of any termination
      payment (including any Unpaid Amount as defined in the Back-to-Back Swap
      Agreement) that may become due to the Pre Assignment Payee as of the
      Assignment Date, an amount equal to the full amount of any such payments.

            (d) Upon (i) the effectiveness of the Fallback Swap Agreement and
      (ii) the payment by GMAC to the Trust in a timely fashion of all
      Delinquent Payments, if any, (x) the Event of Default or Termination Event
      under the Primary Swap Agreement constituting such Designated Event, if
      any, shall be deemed to be cured on and as of the Assignment Date for
      purposes of establishing the rights and obligations of the parties under
      the Fallback Swap Agreement, and (y) no Early Termination Date (as defined
      in the Primary Swap Agreement) may be designated as a result of such
      Designated Event.

      Section 2.02 Additional Contingent Counterparty. If GMAC has acceded to
the rights and obligations of the Primary Swap Counterparty under the Primary
Swap Agreement in accordance with the provisions of this Article II, GMAC shall
have the option to find a Person with the Requisite Rating that will either (i)
enter into an assignment agreement that is substantially similar to this
Agreement pursuant to which such Person will become the Additional Contingent
Counterparty or (ii) enter into swap transaction(s) substantially similar to the
Primary Swap Transaction(s) (the "Replacement Primary Swaps") and a contingent
assignment agreement under which such Person would accede to the rights and
obligations of GMAC under the Fallback Swap Agreement, in which case GMAC will
become the Additional Contingent Counterparty. The Primary Swap Counterparty
shall reimburse GMAC for any reasonable costs associated with finding a party to
serve as the counterparty under the Replacement Primary Swaps or as the
Additional Contingent Counterparty, as the case may be. Any delay or inability
in finding a party to serve as the counterparty under the Replacement Primary
Swaps or as the Additional Contingent Counterparty will not result in the
occurrence of a Termination Event, an Event of Default or otherwise lead to the
designation of an Early Termination Date under the Fallback Swap Agreement.

      Section 2.03 Notice. The Primary Swap Counterparty agrees that, to the
extent that it has actual knowledge that it will be unable to make a payment or
delivery on a scheduled payment date under the Primary Swap Agreement, it shall
provide notice to the Trust of such inability at least two Business Days prior
to such scheduled payment date. This Section 2.03 shall not be construed to
obligate the Primary Swap Counterparty to undertake any affirmative

                                       5


action or inquiry to ascertain whether it will be able to make any such payment
or delivery. Any failure by the Primary Swap Counterparty to provide notice to
the Trust of such inability shall be without prejudice to the Primary Swap
Counterparty's rights under this Agreement and the Primary Swap Agreement.

                                  ARTICLE III

                                  MISCELLANEOUS

      Section 3.01 Miscellaneous.

            (a) Entire Agreement. This Agreement, the Primary Swap Agreement and
      the Back-to-Back Swap Agreement constitute the entire agreement and
      understanding of the parties with respect to the subject matter thereof
      and supersede all oral communications and prior writings (except as
      otherwise provided therein) with respect thereto.

            (b) Counterparts. This Agreement may be executed and delivered in
      counterparts (including by facsimile transmission) each of which will be
      deemed an original.

            (c) Headings. The headings used in this agreement are for
      convenience of reference only and are not to affect the construction of or
      to be taken into consideration in interpreting this Agreement.

            (d) GOVERNING LAW. THIS AGREEMENT SHALL BE GOVERNED BY, AND
      CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK WITHOUT
      REFERENCE TO ITS CONFLICT OF LAW PROVISIONS BUT WITHOUT PREJUDICE TO THE
      PROVISIONS OF SECTION 5-1401 OF ITS GENERAL OBLIGATIONS LAW, AND THE
      OBLIGATIONS, RIGHTS AND REMEDIES OF THE PARTIES HEREUNDER SHALL BE
      DETERMINED IN ACCORDANCE WITH SUCH LAWS.

            (e) Notices. All demands, specifications and notices to a party
      hereto under this Agreement will be made pursuant to the provisions of the
      Primary Swap Agreement or the Back-to-Back Swap Agreement, as applicable.

            (f) No Waiver. Notwithstanding any other provision in this Agreement
      to the contrary, no full or partial failure to exercise and no delay in
      exercising, on the part of any party hereto, any right, remedy, power or
      privilege under this Agreement, regardless of the frequency or constancy
      of such failure or delay, shall operate in any way as a waiver thereof by
      such party.

            (g) Inconsistencies. Except as expressly provided herein, the
      Primary Swap Agreement shall not be deemed to be amended hereby in any
      respect. In the event of any inconsistencies between the provisions of
      this Agreement and those of the Primary Swap Agreement or the Back-to-Back
      Swap Agreement, the provisions hereof shall prevail.

            (h) Amendments. This Agreement may not be amended except by the
      execution of a written instrument by all parties hereto.

                                       6


            (i) Limitation of Liability. It is expressly understood and agreed
      by the parties hereto that (a) this Agreement is executed and delivered by
      Deutsche Bank Trust Company Delaware, not in its individual capacity but
      solely as Owner Trustee of Capital Auto Receivables Asset Trust 2004-2 in
      the exercise of the powers and authority conferred and vested in it, (b)
      each of the representations, undertakings and agreements herein made on
      the part of the Trust is made and intended not as personal
      representations, undertakings and agreements by Deutsche Bank Trust
      Company Delaware but is made and intended for the purpose for binding only
      the Trust, (c) nothing herein contained shall be construed as creating any
      liability on Deutsche Bank Trust Company Delaware in its individual,
      corporate capacity, to perform any covenant either expressed or implied
      contained herein, all such liability, if any, being expressly waived by
      the parties hereto and by any Person claiming by, through or under the
      parties hereto and (d) under no circumstances shall Deutsche Bank Trust
      Company Delaware be personally liable for the payment of any indebtedness
      or expenses of the Trust or be liable for the breach or failure of any
      obligation, representation, warranty or covenant made or undertaken by the
      Trust under this Agreement or any other related documents.

                                       7


            IN WITNESS WHEREOF, the parties have executed this agreement by
      their duly authorized officers as of the date hereof.

                                             CAPITAL AUTO RECEIVABLES ASSET
                                             TRUST 2004-2

                                             By: DEUTSCHE BANK TRUST COMPANY
                                                 DELAWARE, not in its individual
                                                 capacity but solely as Owner
                                                 Trustee

                                             By: /s/ Eva Aryeetey
                                                 ------------------------------
                                             Name: Eva Aryeetey
                                             Title: Attorney-In-Fact

                                             GENERAL MOTORS ACCEPTANCE
                                             CORPORATION

                                             By: /s/ Carl J. Vannatter
                                                 -------------------------------
                                             Name: Carl J. Vannatter
                                             Title: Director - Global
                                                    Securitization

                                             CREDIT SUISSE FIRST BOSTON
                                             INTERNATIONAL

                                             By: /s/ Carole Villoresi
                                                 ------------------------------
                                             Name: Carole Villoresi
                                             Title: Authorized Signatory

                                             By: /s/ Suanne Dunn
                                                 -------------------------------
                                             Name: Suanne Dunn
                                             Title: Authorized Signatory