Sec Form 4 Filing - Weichai America Corp. @ POWER SOLUTIONS INTERNATIONAL, INC. - 2025-08-14

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Weichai America Corp. 2. Issuer Name and Ticker or Trading Symbol POWER SOLUTIONS INTERNATIONAL, INC. [ PSIX] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 3100 GOLF ROAD, 3. Date of Earliest Transaction (MM/DD/YY) 08/14/2025 (Street) ROLLING MEADOWS, IL60008 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 08/14/2025 S( 1 ) 7,136 D $ 81.8007 ( 2 ) 11,456,688 I See Explanation of Responses ( 12 ) Common Stock 08/14/2025 S( 1 ) 28,319 D $ 82.6846 ( 3 ) 11,428,369 I See Explanation of Responses ( 12 ) Common Stock 08/14/2025 S( 1 ) 30,760 D $ 83.5042 ( 4 ) 11,397,609 I See Explanation of Responses ( 12 ) Common Stock 08/14/2025 S( 1 ) 12,430 D $ 84.373 ( 5 ) 11,385,179 I See Explanation of Responses ( 12 ) Common Stock 08/14/2025 S( 1 ) 10,485 D $ 85.6346 ( 6 ) 11,374,694 I See Explanation of Responses ( 12 ) Common Stock 08/14/2025 S( 1 ) 14,386 D $ 86.4457 ( 7 ) 11,360,308 I See Explanation of Responses ( 12 ) Common Stock 08/14/2025 S( 1 ) 8,834 D $ 87.6413 ( 8 ) 11,351,474 I See Explanation of Responses ( 12 ) Common Stock 08/14/2025 S( 1 ) 13,929 D $ 88.3369 ( 9 ) 11,337,545 I See Explanation of Responses ( 12 ) Common Stock 08/14/2025 S( 1 ) 9,312 D $ 89.3299 ( 10 ) 11,328,233 I See Explanation of Responses ( 12 ) Common Stock 08/14/2025 S( 1 ) 255 D $ 90.2445 ( 11 ) 11,327,978 I See Explanation of Responses ( 12 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Weichai America Corp. 3100 GOLF ROAD ROLLING MEADOWS, IL60008 X Weichai Power Co., Ltd. SECTION A 197, FU SHOU EAST STREET HIGH-TECH INDUSTRIAL DEV. ZONE WEIFANG, SHANDONG PROVINCE, F4261061 X Shandong Heavy Industry Group Co., Ltd. #40-1 YANZI SHAN WEST ROAD JINAN, SHANDONG PROVINCE, F4250014 X Signatures /s/ Jinguang Liu (aka Jin Liu), Chief Financial Officer, Weichai America Corp. 08/18/2025 Signature of Reporting Person Date /s/ Chenglong Sun, Authorized Representative, Weichai Power Co., Ltd. 08/18/2025 Signature of Reporting Person Date /s/ Chenglong Sun, Authorized Representative, Shandong Heavy Industry Group Co., Ltd. 08/18/2025 Signature of Reporting Person Date

Explanation of Responses:

( 1 )These transactions occurred pursuant to broker-dealer sales conducted in accordance with Rule 144 under the Securities Act of 1933, as amended. ( 2 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $81.58 to $81.925, inclusive. The Reporting Persons (as defined below) undertake to provide the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares of Common Stock sold at each separate price within the range set forth in this footnote. ( 3 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $82.1651 to $82.9893, inclusive. The Reporting Persons undertake to provide the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares of Common Stock sold at each separate price within the range set forth in this footnote. ( 4 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $83.00 to $83.995, inclusive. The Reporting Persons undertake to provide the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares of Common Stock sold at each separate price within the range set forth in this footnote. ( 5 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $84.00 to $84.87, inclusive. The Reporting Persons undertake to provide the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares of Common Stock sold at each separate price within the range set forth in this footnote. ( 6 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $85.09 to $85.995, inclusive. The Reporting Persons undertake to provide the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares of Common Stock sold at each separate price within the range set forth in this footnote. ( 7 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $86.00 to $86.93, inclusive. The Reporting Persons undertake to provide the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares of Common Stock sold at each separate price within the range set forth in this footnote. ( 8 ) The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $87.00 to $87.975, inclusive. The Reporting Persons undertake to provide the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares of Common Stock sold at each separate price within the range set forth in this footnote. ( 9 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $88.01 to $88.975, inclusive. The Reporting Persons undertake to provide the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares of Common Stock sold at each separate price within the range set forth in this footnote. ( 10 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $89.00 to $89.9876, inclusive. The Reporting Persons undertake to provide the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares of Common Stock sold at each separate price within the range set forth in this footnote. ( 11 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $90.1147 to $90.3675, inclusive. The Reporting Persons undertake to provide the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares of Common Stock sold at each separate price within the range set forth in this footnote. ( 12 )This report is filed jointly by Weichai America Corp., Weichai Power Co., Ltd. and Shandong Heavy Industry Group Co., Ltd. (collectively, the "Reporting Persons"). Weichai America Corp. is the direct owner of the Common Stock referenced in this report and shares the power to vote and the power to dispose of all of such shares of Common Stock with the other Reporting Persons. No individual has beneficial ownership over the Common Stock beneficially owned by the Reporting Persons.

Remarks: Exhibit List: Exhibit 24.1 - Power of Attorney (Weichai Power Co., Ltd.), incorporated by reference to Exhibit 24.1 to the Form 4 filed by Reporting Persons with the Securities and Exchange Commission on August 14, 2025 Exhibit 24.2 - Power of Attorney (Shandong Heavy Industry Group Co., Ltd.), incorporated by reference to Exhibit 24.2 to the Form 4 filed by Reporting Persons with the Securities and Exchange Commission on August 14, 2025

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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