UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): August 8, 2013

CARMAX AUTO OWNER TRUST 2013-3

(Issuing Entity with respect to Securities)

CARMAX BUSINESS SERVICES, LLC

(Sponsor with respect to Securities)

CARMAX AUTO FUNDING LLC

(Depositor with respect to Securities)

12800 Tuckahoe Creek Parkway

Richmond, VA 23238-1115

(Address of principal executive offices of registrant, including zip Code)

Registrant’s telephone number, including area code: (804) 935-4512

Former name or former address, if changed since last report: Not applicable

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

CarMax Auto Funding LLC, a Delaware limited liability company, (the “Depositor”) has registered an issuance of $14,000,000,000 aggregate principal amount of various classes of asset backed notes on Form S-3 (Commission File No. 333-189212), filed on June 10, 2013, and as amended by Pre-Effective Amendment No. 1 on June 21, 2013 (as amended, the “Registration Statement”).

On August 8, 2013 (the “Closing Date”), the Depositor entered into an Amended and Restated Trust Agreement, a copy of which is filed as an exhibit hereto, with U.S. Bank Trust National Association, as owner trustee (the “Owner Trustee”), relating to CarMax Auto Owner Trust 2013-3 (the “Issuing Entity”), a Delaware statutory trust created on April 3, 2013. On the Closing Date, CarMax Business Services, LLC (“CarMax Business Services”) and the Depositor entered into a Receivables Purchase Agreement, a copy of which is filed as an exhibit hereto, pursuant to which specified motor vehicle retail installment sale contracts and related property were sold by CarMax Business Services to the Depositor. On the Closing Date, the Issuing Entity, the Depositor, CarMax Business Services, as servicer, and Wells Fargo Bank, National Association, as backup servicer, entered into a Sale and Servicing Agreement, a copy of which is filed as an exhibit hereto, pursuant to which motor vehicle retail installment sale contracts and related property were transferred by the Depositor to the Issuing Entity. On the Closing Date, the Issuing Entity issued to the Depositor the Class A-1 Asset-backed Notes, Class A-2 Asset-backed Notes, Class A-3 Asset-backed Notes, Class A-4 Asset-backed Notes, Class B Asset-backed Notes, Class C Asset-backed Notes and Class D Asset-backed Notes, having an aggregate original principal amount of $1,000,000,000 pursuant to an Indenture entered into between the Issuing Entity and Wells Fargo Bank, National Association, as indenture trustee (the “Indenture Trustee”), on the Closing Date, a copy of which is filed as an exhibit hereto. On the Closing Date, the Issuing Entity, the Indenture Trustee and CarMax Business Services, as administrator, entered into an Administration Agreement, a copy of which is filed as an exhibit hereto, pursuant to which the administrator agreed to perform certain duties and obligations of the Issuing Entity and the Owner Trustee under the transaction documents.

The prospectus supplement, dated July 31, 2013, issued under the Registration Statement, contains statistical information regarding the characteristics of the statistical pool of receivables as of June 30, 2013, the statistical calculation date. Set forth below is information as of July 31, 2013 (the “Cutoff Date”) regarding the characteristics of the pool of receivables transferred to the Issuing Entity on the Closing Date.

Composition of the Receivables

as of the Cutoff Date

As of the Cutoff Date, the weighted average FICO^®* score of the Receivables is 700.1, with the minimum FICO score being 471 and the maximum FICO score being 900. Additionally, 90% of the Pool Balance as of the Cutoff Date is composed of obligors with FICO scores between 567 and 838, with 5% of obligor FICO scores (based on Principal Balance) exceeding 838 and 5% of obligor FICO scores (based on Principal Balance) falling below 567. The calculations in this paragraph reflect only Receivables with obligors that have a FICO score at the time of application. The percentage of obligors that did not have a FICO score at the time of application was 0.68% based on Principal Balance.

1

Distribution of the Receivables by Remaining Term to Maturity

as of the Cutoff Date

Distribution of the Receivables by Original Term to Maturity

as of the Cutoff Date

Distribution of the Receivables by Obligor Mailing Address

as of the Cutoff Date

2

Each state included in the “other” category in the distribution by obligor mailing address table accounted for not more than 1.07% of the total number of Receivables and not more than 1.07% of the Pool Balance, in each case as of the Cutoff Date.

Distribution of the Receivables by Financed Vehicle Model Year

as of the Cutoff Date

3

Distribution of the Receivables by Contract Rate

as of the Cutoff Date

Distribution of the Receivables by Original Principal Balance

as of the Cutoff Date

The average original Principal Balance of the Receivables was $18,850.13 as of the Cutoff Date.

4

Distribution of the Receivables by Remaining Principal Balance

as of the Cutoff Date

The average remaining Principal Balance of the Receivables was $15,933.46 as of the Cutoff Date.

Pool Underwriting

In the pool of Receivables, 51,048 Receivables having an aggregate Principal Balance as of the Cutoff Date of $810,715,829.10 (representing 81.07% of the aggregate Principal Balance of the pool of Receivables) were automatically approved. The remaining Receivables were approved after review by a credit underwriter based on the decision rules established by CarMax Auto Finance. As described in the prospectus dated July 25, 2013, CarMax Auto Finance does not consider any of the Receivables to constitute exceptions to its underwriting standards.

Reserve Account

On the Closing Date, the Depositor deposited $2,500,000.00 into the reserve account.

5

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, the depositor has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

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EXHIBIT INDEX