EXECUTION COPY SPREAD ACCOUNT AGREEMENT

Exhibit 10.4

EXECUTION COPY

SPREAD ACCOUNT AGREEMENT

among

AMERICREDIT AUTOMOBILE RECEIVABLES TRUST 2005-A-X,

as Issuer,

XL CAPITAL ASSURANCE INC.,

as Insurer,

and

WELLS FARGO BANK, NATIONAL ASSOCIATION,

as Trustee, as Trust Collateral Agent and as Collateral Agent

Dated as of January 27, 2005

TABLE OF CONTENTS

i

ii

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SPREAD ACCOUNT AGREEMENT

This SPREAD ACCOUNT AGREEMENT, dated as of January 27, 2005 (this “Agreement”), is among AMERICREDIT AUTOMOBILE RECEIVABLES TRUST 2005-A-X, as issuer (the “Issuer”), XL CAPITAL ASSURANCE INC., as insurer (the “Insurer”), and WELLS FARGO BANK, NATIONAL ASSOCIATION as trustee (in such capacity, the “Trustee” ), as trust collateral agent (in such capacity the “Trust Collateral Agent”) and as collateral agent (in such capacity, the “Collateral Agent”).

RECITALS

WHEREAS, the Issuer was formed pursuant to the trust agreement dated as of January 6, 2005 as amended and restated as of January 27, 2005 (as amended from time to time, the “Trust Agreement”), between AFS SenSub Corp., as seller, (the ”Seller”) and Wilmington Trust Company, as owner trustee (the “Owner Trustee”).

WHEREAS, pursuant to a sale and servicing agreement, dated as of January 27, 2005 (the “Sale and Servicing Agreement”) among the Issuer, the Seller, the Servicer, the Trust Collateral Agent and the Backup Servicer, the Seller sold to the Issuer all of its right, title and interest in and to the Receivables and Other Conveyed Property.

WHEREAS, pursuant to the indenture, dated as of January 27, 2005 (the ”Indenture”), among the Issuer, the Trustee and the Trust Collateral Agent, the Issuer pledged all of its right, title and interest in and to the Collateral to the Trust Collateral Agent on behalf of the Issuer Secured Parties.

WHEREAS, the Issuer requested that the Insurer issue the Note Policy to the Trustee to guarantee payment of the Insured Payments on each Distribution Date, in respect of the Notes.

WHEREAS, in consideration of the issuance of the Note Policy, the Issuer and the Servicer have agreed that the Insurer shall have certain rights as Controlling Party to the extent set forth in the Basic Documents, with respect to the Collateral.

In consideration of the premises, and for other good and valuable consideration, the adequacy, receipt and sufficiency of which are hereby acknowledged the parties hereto agree as follows:

ARTICLE I

DEFINITIONS

Section 1.01. Definitions. Unless otherwise defined in this Agreement, the following terms shall have the following meanings:

“Accelerated Payment Amount Shortfall” has the meaning set forth in Section 1.1 of the Sale and Servicing Agreement.

“AmeriCredit” means AmeriCredit Financial Services, Inc.

“Cash Collateral Deposit” has the meaning set forth in Section 3.06(a).

“Cash Collateralized Receivable” means a Delinquent Receivable for which a deposit has been made to the Spread Account by the Servicer pursuant to Section 3.06(a).

“Collateral Agent” means, initially Wells Fargo Bank, National Association, in its capacity as collateral agent on behalf of the Issuer Secured Parties, including its successors in interest, until a successor Person shall have become the Collateral Agent pursuant to Section 4.05 and thereafter “Collateral Agent” shall mean such successor Person.

“Collateral Agent Fee” means as designated in the fee letter between Collateral Agent and AmeriCredit.

“Controlling Party” means the Person designated as the Controlling Party at such time pursuant to Section 6.01.

“Cumulative Net Loss” means the positive difference between (i) the sum of (A) the aggregate Principal Balance of all Liquidated Receivables plus (B) aggregate Cram Down Losses minus (ii) Liquidation Proceeds received with respect to the Receivables described in clause (i).

“Cumulative Net Loss Ratio” means the ratio, expressed as a percentage, computed by dividing: (a) the sum (without duplication) of (i) Cumulative Net Losses and (ii) the product of (x) 0.50 and (y) the aggregate Principal Balance of all Receivables which are more than ninety (90) days past due as of the end of the related Collection Period; by (b) the Initial Pool Balance.

“Default” means, (i) if the Insurer is then the Controlling Party, any Insurance Agreement Event of Default and (ii) if the Trustee is then the Controlling Party, any Event of Default under Section 5.1 of the Indenture.

“Defaulted Receivable” means a Receivable (i) with respect to which (A) 10% or more of a Scheduled Receivables Payment is more than ninety (90) days past due, (B) the Servicer has repossessed the related Financed Vehicle (and any applicable redemption period has expired), or (C) such Receivable is in default and the Servicer has charged-off such Receivable in accordance with the credit and collection policy attached as Schedule C to the Sale and Servicing Agreement or otherwise has determined in good faith that payment thereunder are not likely to be resumed, or (ii) which is a Sold Receivable.

“Delinquency Ratio” means, the ratio (expressed as a percentage) computed by dividing: (a) the aggregate Principal Balance of all Receivables which were Delinquent Receivables as of the close of business on the last day of the related Collection Period minus the aggregate Principal Balance of all Cash Collateralized Receivables by (b) the sum of the aggregate Principal Balance of all Receivables as of the close of business on the first day of the related Collection Period.

2

“Delinquent Receivable” means a Receivable with respect to which 10% or more of a Scheduled Receivables Payment is more than sixty (60) days past due (excluding (i) Receivables which the Servicer has repossessed the related Financed Vehicle and (ii) Receivables which have become Liquidated Receivables).

“Final Termination Date” means the date that is the later of (i) the Insurer Termination Date and (ii) the Trustee Termination Date.

“Gross Default Ratio” means, the ratio expressed as a percentage, the numerator of which is the aggregate Principal Balance of all Defaulted Receivables since the Closing Date and the denominator of which is the Initial Pool Balance.

“Initial Pool Balance” means the Pool Balance as of the Cutoff Date.

“Insured Payments” has the meaning set forth in the Note Policy.

“Insurer Termination Date” means the date which is the latest of (i) the date of the expiration of the Note Policy and the cancellation and return thereof to the Insurer, (ii) the date on which the Insurer shall have received payment and performance in full of all Insurer Issuer Secured Obligations and (iii) the latest date on which any payment referred to above could be avoided as a preference or otherwise under the United States Bankruptcy Code or any other similar federal or state law relating to insolvency, bankruptcy, rehabilitation, liquidation or reorganization, as specified in an Opinion of Counsel delivered to the Collateral Agent, the Insurer and the Trustee.

“Issuer” means AmeriCredit Automobile Receivables Trust 2005-A-X.

“Issuer Secured Obligations” means the Issuer Secured Obligations under the Indenture and the “Issuer Insured Obligations” under any Related Series Spread Account Agreement.

“Issuer Secured Parties” means the Issuer Secured Parties under the Indenture and the “Issuer Secured Parties” under any Related Series Spread Account Agreement.

3

“Level 1 Cumulative Net Loss Test” means, for any Distribution Date specified below, the Cumulative Net Loss Ratio for the related Collection Period is greater than the percentage set forth opposite such Distribution Date:

“Level 1 Delinquency Test” means, for any Distribution Date, the arithmetic average of the monthly Delinquency Ratios for the three immediately preceding Collection Periods is greater than the percentage set forth opposite such Distribution Date plus 0.25% for each November through April Distribution Dates:

4

“Level 1 Gross Default Test” means, for any Distribution Date specified below, the Gross Default Ratio for the related Collection Period is greater than the percentage set forth opposite such Distribution Date: