U.S. · Vehicle safety · 49 CFR 571.103
FMVSS 103: Windshield Defrosting and Defogging Systems explained.
Purpose, scope, application and key requirements of 49 CFR 571.103, quoted from the eCFR, with a finder for its 6 section headings.
FMVSS 103 is the federal motor vehicle safety standard at 49 CFR 571.103. Its text states its scope as: This standard specifies requirements for windshield defrosting and defogging systems. The standard has 4 top-level sections and 6 numbered headings in all.
Find a section
What FMVSS 103 says it is for
The eCFR heads this section "Standard No. 103; Windshield defrosting and defogging systems." Under 49 CFR part 571, the Federal Motor Vehicle Safety Standards are the numbered standards that set safety performance requirements for motor vehicles and equipment. The text below is quoted from 571.103 as current through October 29, 2026.
This standard specifies requirements for windshield defrosting and defogging systems.
What it applies to
The application section of the standard says:
This standard applies to passenger cars, multipurpose passenger vehicles, trucks, and buses.
Applicability is decided by the text of the standard as written, including any exclusions it lists, and by the date-specific rules in it. This page does not decide whether a particular vehicle or item is covered.
How the standard is organized
The eCFR text of 571.103 has these top-level sections:
- S1: Scope
- S2: Application
- S3: Definitions. Road load
- S4: Requirements
In all, the text has 6 numbered headings. Use the finder above to search them; for example, a search for "test" lists the headings that mention tests.
Key requirements, quoted from the text
These are excerpts from the requirements sections of 571.103, in the order the standard presents them. Long paragraphs are shortened where marked with [...]; the eCFR has the complete text, tables and figures, which this page omits.
S4 Requirements. (a) Except as provided in paragraph (b) of this section, each passenger car shall meet the requirements specified in S4.1, S4.2, and S4.3, and each multipurpose passenger vehicle, truck, and bus shall meet the requirements specified in § 4.1. (b) Each passenger car, multipurpose passenger vehicle, truck, and bus manufactured for sale in the noncontinental United States may, at the option of the manufacturer, have a windshield defogging system which operates either by applying heat to the windshield or by dehumidifying the air inside the passenger compartment of the vehicle, in lieu of meeting the requirements specified by paragraph (a) of this section.
S4.1 Each vehicle shall have a windshield defrosting and defogging system. S4.2 Each passenger car windshield defrosting and defogging system shall meet the requirements of section 3 of SAE Recommended Practice J902 (1964) (incorporated by reference, see § 571.5) when tested in accordance with S4.3, except that “the critical area” specified in paragraph 3.1 of SAE Recommended Practice J902 (1964) shall be that established as Area C in accordance with Motor Vehicle Safety Standard No. 104, “Windshield Wiping and Washing Systems,” and “the entire windshield” specified in paragraph 3.3 of SAE Recommended Practice J902 (1964) shall be that established as Area A in accordance with § 571.104.
S4.3 Demonstration procedure. The passenger car windshield defrosting and defogging system shall be tested in accordance with the portions of paragraphs 4.1 through 4.4.7 of SAE Recommended Practice J902 (1964) or SAE Recommended Practice J902a (1967) (both incorporated by reference, see § 571.5) applicable to that system, except that— (a) During the first 5 minutes of the test: (1) For a passenger car equipped with a heating system other than a heat exchanger type that uses the engine's coolant as a means to supply the heat to the heat exchanger, the warm-up procedure is that specified by the vehicle's manufacturer for cold weather starting, except that connection to a power or heat source external to the vehicle is not permitted. [...]
Limits of this page
This page quotes the text of 49 CFR 571.103 as published in the eCFR, current through October 29, 2026. It omits tables, figures, cross-referenced test procedures in other parts, and the preambles and rulemaking history that explain the rule. It does not tell you whether a given vehicle, part or product complies, how to run a test, or what a manufacturer must certify. Compliance questions go to the manufacturer's engineers, qualified counsel or NHTSA. The eCFR is an editorial compilation, not the official legal edition of the Federal Register.
Sources
Sources opened and read November 2, 2026.
Frequently asked questions
What is FMVSS 103?
FMVSS 103 is codified at 49 CFR 571.103, headed "Standard No. 103; Windshield defrosting and defogging systems". Its scope text reads: This standard specifies requirements for windshield defrosting and defogging systems.
What does FMVSS 103 apply to?
Its application section reads: This standard applies to passenger cars, multipurpose passenger vehicles, trucks, and buses.
How is FMVSS 103 organized?
The eCFR text has these top-level sections: S1 Scope; S2 Application; S3 Definitions. Road load; S4 Requirements. The finder on this page searches all 6 numbered section headings.
Where does FMVSS 103 define its terms?
In S3 Definitions. Road load. This page quotes 0 of the 0 defined terms found there, from the eCFR.
Where are the test conditions and procedures in FMVSS 103?
The headings that cover tests, conditions or procedures include: S4.3 Demonstration procedure. Read the full text in the eCFR for the exact conditions.
Is this page the official text of FMVSS 103?
No. It quotes parts of the eCFR text of 49 CFR 571.103 (current through October 29, 2026, read November 2, 2026) and is an unofficial reference. The eCFR is not the official legal edition of the Federal Register, and the standard changes by rulemaking, so check the current text and NHTSA before relying on it.
Not legal or compliance advice
This page is general information drawn from the sources listed, not legal, engineering or compliance advice, and it is not run by any government agency. Rules, forms and dates change and your agency, base jurisdiction or enforcement officer decides your case, so confirm with the office named on this page before you rely on it. Everything runs in your browser; nothing you enter is sent anywhere.