CFR is applicable to every motor vehicle sold, imported, etc within the USA. It is incorporated by every state in the USA and therefore enforcement extends to every state and/or local Leo.
Examples, driving a Jeep with doors remove, done? Yes! Legal? No! Enforces? Sometimes. PA law prohibits the use of cats eyes in brake lights. State trooper's enforce, local don't. We all know some folks riding cruisers with aftermarket exhaust. Most cops don't enforce, but if you get stopped at a safety check, or pulled, the cops will look for the EPA stamp. Not there and bike gets impounded. Where are most of these codes found? CFR.
Do what you want, but know the law.
I do agree with you that it applies to requirements for vehicles to be manufactured, imported, or sold in the US. I also will agree that I know the law. I'm a NC State trooper and I've been in law enforcement coming up on 17 years. One thing I do know is motor vehicle law (Now I can't help with your oil issue. My 11 used about a 1/2 to 3/4 of a quart about every 6k miles). I will tell you that I can't enforce federal law. When I was a local officer, I couldn't either. I'll give another example. I was recently trained in Federal Motor Carrier safety regulations (FMCSR) that apply to commercial motor vehicles (big trucks). NC had to adopt the federal regulations for me to be able to enforce them. When I do enforce the federal regs, its civil in nature and only effects the drivers/company's federal safety score. However, I can also criminally charge under NC general statue for seeking to avid FMCSR.
But don't take my word for it. Here is an article on it from Duke law
From the footnotes in the beginning: "5 See infra Part I.B (discussing state enforcement of federal law). This Article focuses on direct state enforcement of federal civil law. States may participate in various ways in the enforcement of federal criminal law as well, for example by arresting individuals for federal offenses. But states lack power to enforce federal criminal law directly, such as by prosecuting federal offenders themselves in state or federal court. States play a similar role with respect to federal immigration law. Under Section 287(g) of the Immigration and Naturalization Act, states or localities can sign a Memorandum of Understanding with the federal government to deputize officials to enforce federal immigration law "in relation to the investigation, apprehension, or detention of [noncitizens] in the United States." 8 U.S.C. § 1357(g) (2006). Deputized state officials obtain federal training from the federal Immigration and Customs Enforcement agency (ICE) and work under ICE's supervision. See Jennifer M. Chacon, A Diversion of Attention? Immigration Courts and the Adjudica- tion of Fourth and Fifth Amendment Rights, 59 DuKE L.J. 1563, 1582-86 (2010) (discussing Section 287(g) arrangements). States also contribute to the criminal enforcement of immi- gration law by investigating and arresting offenders, though again they lack the authority to prosecute offenders directly. See 8 U.S.C. § 1252c (2006) (authorizing state and local law enforcement officials to arrest and detain certain illegal aliens "for such period of time as may be required for the [ICE] to take the individual into Federal custody for purposes of deporting or removing the alien from the United States"); United States v. Santana- Garcia, 264 F.3d 1188, 1193-94 (10th Cir. 2001) (recognizing implicit authority for state police to detain suspects for federal immigration violations); Gonzales v. City of Peoria"
and from page 708
"States have no inherent power to enforce federal statutory law"
Now NC law as it pertains to brake lamps:
GS 20-129 (G) states: (g) No person shall sell or operate on the highways of the State any motor vehicle, motorcycle or motor-driven cycle, manufactured after December 31, 1955, unless it shall be equipped with a stop lamp on the rear of the vehicle. The stop lamp shall display a red or amber light visible from a distance of not less than 100 feet to the rear in normal sunlight, and shall be actuated upon application of the service (foot) brake. The stop lamp may be incorporated into a unit with one or more other rear lamps. (1937, c. 407, s. 92; 1939, c. 275; 1947, c. 526; 1955, c. 1157, ss. 3-5, 8; 1957, c. 1038, s. 1; 1967, cc. 1076, 1213; 1969, c. 389; 1973, c. 531, ss. 1, 2; 1979, c. 175; 1981, c. 549, s. 1; 1985, c. 66; 1987, c. 611; 1989 (Reg. Sess., 1990), c. 822, s. 1; 1991, c. 18, s. 1; 1999-281, s. 1.)
There is no provision or exclusion of a flashing brake light. In fact, almost every new fire truck and ambulance (around here) have flashing LED brake lights now.