SECOND SUPPLEMENTAL INDENTURE

Exhibit 10.4

CSK AUTO, INC.

4  ⁵ / 8 % Senior Exchangeable Notes due 2025

SECOND SUPPLEMENTAL INDENTURE

Dated as of July 27, 2006

with respect to the

INDENTURE

Dated as of December 19, 2005

THE BANK OF NEW YORK TRUST COMPANY, N.A.,

as Trustee

SECOND SUPPLEMENTAL INDENTURE

SECOND SUPPLEMENTAL INDENTURE dated as of July 27, 2006 (this “Supplemental Indenture ” ) among CSK Auto, Inc., an Arizona corporation (the “ Company ”), CSK Auto Corporation, a Delaware corporation and the parent of the Company (the “ Issuer ”), CSKAUTO.COM, Inc., a Delaware corporation (the “ Subsidiary Guarantor” ), and The Bank of New York Trust Company, N.A., a national banking association, as trustee under the indenture referred to below (the “ Trustee” ).

WITNESSETH

A. WHEREAS, the Company, the Issuer and the existing Subsidiary Guarantor have heretofore executed and delivered to the Trustee an Indenture (as amended, supplemented or otherwise modified, the “ Indenture” ) dated as of December 19, 2005, providing for the issuance of the Company’s 4  ⁵ / 8 % Senior Exchangeable Notes due 2025 (the “ Notes” ), initially in the aggregate principal amount of up to $100,000,000.

B. WHEREAS, pursuant to and in accordance with Section 10.02 of the Indenture, the Company has obtained, on the date hereof, the consent of the holders of the Notes representing not less than a majority in aggregate Principal Amount of the outstanding Notes to the amendments to the Indenture set forth in this Supplemental Indenture.

NOW, THEREFORE, in consideration of the foregoing and for other good and valuable consideration, the receipt of which is hereby acknowledged, it is mutually covenanted and agreed for the equal and ratable benefit of the holders of the Notes as follows:

SECTION 1. Defined Terms . As used in this Supplemental Indenture, terms defined in the Indenture or in the preamble or recital hereto are used herein as therein defined. The words “herein,” “hereof” and hereby and other words of similar import used in this Supplemental Indenture refer to this Supplemental Indenture as a whole and not to any particular section hereof.

SECTION 2. Amendments to Indenture . At such time as the Company delivers written notice to the Trustee and The Altman Group, Inc., the Depositary for the Notes for purposes of a tender offer and consent solicitation for the Notes, that Notes representing at least a majority in aggregate Principal Amount of outstanding Notes not owned by the Company or its Affiliates tendered (and not validly withdrawn) have been accepted pursuant to the Company’s Letter of Consent and Waiver dated July 27, 2006:

“ Covenant Reversion Date ” means 11:59 p.m., New York City time, on June 30, 2007.

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“ Exchange Price ” as of any day means the Principal Amount divided by the Exchange Rate as of such date and rounded to the nearest cent. The Exchange Price shall be $16.50 per share of Common Stock as of July 27, 2006.

Section 4.06. Rule 144A Information Requirement . Within the period prior to the expiration of the holding period applicable to sales thereof under Rule 144(k) under the Securities Act (or any successor provision), the Company and the Issuer covenant and agree that they shall, during any period in which neither the Company nor the Issuer is subject to Section 13 or 15(d) under the Exchange Act, make available to any holder or beneficial holder of Notes or any Common Stock issued upon exchange thereof which continue to be Restricted Securities in connection with any sale thereof and any prospective purchaser of Notes or such Common Stock designated by such holder or beneficial holder, the information required pursuant to Rule 144A(d)(4) under the Securities Act upon the request of any holder or beneficial holder of the Notes or such Common Stock and it will take such further action as any holder or beneficial holder of such Notes or such Common Stock may reasonably request, all to the extent required from time to time to enable such holder or beneficial holder to sell its Notes or Common Stock without registration under the Securities Act within the limitation of the exemption provided by Rule 144A, as such Rule may be amended from time to time. Upon the request of any holder or any beneficial holder of the Notes or such Common Stock, the Company and the Issuer will deliver to such holder a written statement as to whether it has complied with such requirements.

Section 4.08. Compliance Certificate . The Company shall, except as otherwise provided in this Section 4.08, deliver to the Trustee, within one hundred twenty calendar days after the end of each fiscal year of the Company (which fiscal year of the Company presently ends on the Sunday nearest to January 31), a certificate signed by either the principal executive officer, principal financial officer or principal accounting officer of the Company,

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stating whether or not to the best knowledge of the signer thereof the Company or the Issuer is in default in the performance and observance of any of the terms, provisions and conditions of this Indenture (without regard to any period of grace or requirement of notice provided hereunder) and, if the Company or the Issuer shall be in default, specifying all such defaults and the nature and the status thereof of which the signer may have knowledge (such certificate, a “Compliance Certificate”).

The Company will, except as otherwise provided in this Section 4.08, deliver to the Trustee, promptly upon becoming aware of (i) any default in the performance or observance of any covenant, agreement or condition contained in this Indenture, or (ii) any Event of Default, an Officers’ Certificate specifying with particularity such default or Event of Default and further stating what action the Company or the Issuer has taken, is taking or proposes to take with respect thereto (such certificate, a “Default Certificate”).

Any notice required to be given under this Section 4.08 shall be delivered to a Responsible Officer of the Trustee at its Corporate Trust Office.

Notwithstanding any other provision of this Section 4.08 or this Indenture, (i) the Compliance Certificate that the Company would have been required (but for this sentence) to deliver pursuant to this Section 4.08 at any time before the Covenant Reversion Date shall not be required to be delivered for failure of the Company to comply with Sections 4.08 or 5.04 of this Indenture until the Covenant Reversion Date, and (ii) the Company shall have no obligation to deliver a Default Certificate pursuant to this Section 4.08 relating to the default in the performance or breach of any covenant contained in Sections 4.08 or 5.04 of this Indenture that occurred prior to the Covenant Reversion Date.