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Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minuteDOJ sued California on August 15, 2025, arguing that the state could not enforce heavy-duty truck emissions requirements through the Clean Truck Partnership after the relevant federal waivers were invalidated. On October 31, 2025, a federal judge issued a preliminary injunction blocking CARB from enforcing the Partnership—but not California’s separate Clean Truck Check program or every other truck-emissions obligation.
The U.S. Department of Justice sued California on August 15, 2025, challenging the state’s enforcement of heavy-duty truck emissions requirements through the Clean Truck Partnership. DOJ argues that federal law preempts California from enforcing the underlying vehicle-emissions standards because the relevant federal waivers were invalidated in 2025. The manufacturers joining the case say California cannot accomplish indirectly through a contract what the Clean Air Act prevents it from doing directly through regulation.
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The most important later development was not a final ruling striking down every California truck-emissions rule. On October 31, 2025, the U.S. District Court for the Eastern District of California granted truck manufacturers a preliminary injunction barring the California Air Resources Board from implementing, enforcing, attempting to enforce, or threatening to enforce the Clean Truck Partnership. The order also reached CARB’s related contract lawsuit in Alameda County. The injunction is preliminary, and the available record does not establish a final merits judgment or definitive appellate resolution.
What this means in practical terms: the Clean Truck Partnership’s enforcement is blocked while the federal case proceeds, but California’s separate Clean Truck Check inspection-and-maintenance program remains a distinct obligation. Truck owners and fleets should not interpret the lawsuit as permission to ignore California emissions testing, reporting, roadside inspections, or required repairs.
Timeline of the California truck-emissions dispute
| Date | Development |
|---|---|
| July 5, 2023 | CARB and truck-industry participants signed the Clean Truck Partnership. |
| August 15, 2025 | DOJ announced two federal complaints challenging California’s enforcement of the Partnership. |
| August 2025 | The Federal Trade Commission closed a separate antitrust investigation after receiving written manufacturer commitments concerning the Partnership. |
| October 31, 2025 | The Eastern District of California granted the manufacturers a preliminary injunction against enforcement of the Partnership. |
| March 2026 | A secondary legal-policy tracker reported that the related Alameda County contract case had been stayed because of the federal litigation. This is not a final resolution of either case. |
What was the Clean Truck Partnership?
CARB describes the Clean Truck Partnership as a negotiated agreement signed with the Truck and Engine Manufacturers Association, major heavy-duty truck and engine manufacturers, and Ford. CARB said the participating manufacturers represented more than 90 percent of California’s truck market.
The Partnership was intended to coordinate California’s emissions goals with manufacturers’ need for lead time, regulatory flexibility, and supporting infrastructure as commercial vehicles move toward zero-emission technology. CARB’s materials connect the agreement to several programs, including:
- Advanced Clean Trucks: a manufacturer-sales regulation requiring increasing percentages of zero-emission trucks in California, with different 2035 targets for different truck classes.
- Heavy-Duty Low NOx: CARB’s nitrogen-oxide emissions program, designed to reduce pollution from new heavy-duty engines and vehicles.
- Advanced Clean Fleets: California’s broader fleet-transition framework for increasing the use of zero-emission commercial vehicles.
CARB’s description emphasizes negotiated implementation. The Partnership included commitments involving amendments to legacy-engine provisions, coordination with the EPA’s 2027 heavy-duty nitrogen-oxide rule, manufacturer compliance, and zero-emission infrastructure. In CARB’s telling, the arrangement gave manufacturers additional flexibility and time while preserving California’s emissions and zero-emission objectives.
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DOJ and the manufacturer plaintiffs describe the arrangement differently. Their position is that the Partnership operated as a regulatory backstop: manufacturers agreed to meet specified California requirements regardless of how the underlying legal challenges turned out, while CARB allegedly retained certification and enforcement leverage. That characterization is central to the federal government’s claim that the state was attempting to use a contract to avoid federal preemption.
Why did DOJ challenge California?
The dispute centers on the Clean Air Act’s division of authority between the federal government and the states.
Section 209(a) generally prevents states from adopting or enforcing standards relating to emissions from new motor vehicles or engines. Section 209(b) creates a special waiver process for California. When California has a valid waiver from the Environmental Protection Agency, it may enforce certain vehicle-emissions requirements that other states generally could not adopt independently.
DOJ says EPA had granted waivers for California’s Advanced Clean Trucks and Heavy-Duty Low NOx Omnibus regulations. The federal government’s theory is that congressional resolutions passed in 2025 and signed by President Trump invalidated the relevant waivers. If that position prevails, DOJ argues, the underlying California requirements became preempted by Section 209(a).
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The legal dispute is not limited to whether the Clean Truck Partnership was labeled a contract or a regulation. DOJ argues that California could not enforce the same requirements indirectly after losing the federal authority necessary to enforce them directly. The manufacturers make a similar “indirect regulation” argument and contend that the Partnership’s certification and enforcement mechanisms made compliance effectively mandatory.
California’s position is materially different. CARB’s public materials present the Partnership as a negotiated framework that provided manufacturers flexibility and lead time while advancing emissions-reduction and zero-emission goals. Whether the arrangement is an enforceable contract, a preempted regulatory mechanism, or some combination that must be analyzed provision by provision is a matter for the litigation.
What did the federal court order?
In Daimler Truck North America LLC et al. v. California Air Resources Board et al., No. 2:25-cv-02255, the Eastern District of California granted the truck manufacturers’ request for preliminary relief in part on October 31, 2025.
The order bars CARB from:
- implementing the Clean Truck Partnership;
- enforcing or attempting to enforce it;
- threatening to enforce it; and
- pursuing specific performance of the Partnership in CARB’s related Alameda County contract action.
The court granted relief on the manufacturers’ claim that the Partnership was preempted. However, it did not grant every form of relief requested. For example, the order denied the manufacturers’ separate First Amendment challenge to an executive order.
A preliminary injunction is not the same as a final judgment. It is temporary relief issued while the court considers the case. The order prevents CARB from using the Partnership during the litigation or until the court changes the order, but it does not by itself answer every question about California’s underlying emissions regulations, the 2025 waiver action, or the ultimate scope of federal preemption.
What the injunction does—and does not—change
| Question | Answer |
|---|---|
| Can CARB enforce the Clean Truck Partnership under the preliminary injunction? | Not while the injunction remains in effect, subject to the precise terms of the court’s order. |
| Did the court eliminate every California heavy-duty emissions rule? | No. The verified relief targets enforcement of the Clean Truck Partnership, not every California truck-emissions or inspection requirement. |
| Did the court issue a final ruling on the Clean Air Act dispute? | No. The ruling is preliminary and the broader litigation remains pending in the available record. |
| Can a fleet stop complying with California vehicle-inspection requirements? | No. The Partnership and Clean Truck Check are separate programs. |
| Did the injunction decide the FTC’s antitrust concerns? | No. The FTC handled a separate competition investigation and did not resolve the Clean Air Act preemption question. |
Clean Truck Check is a separate issue for truck owners
California’s Clean Truck Check program is an in-use inspection-and-maintenance program, not the Clean Truck Partnership. CARB says it applies to nearly all diesel and alternative-fuel heavy-duty vehicles with a gross vehicle weight rating above 14,000 pounds that operate on California public roads. That includes vehicles registered in other states when they operate in California.
Depending on the vehicle and applicable requirements, the program involves emissions reporting, compliance fees, emissions testing, roadside inspections, and repairs when emissions-control systems fail. The federal lawsuit and preliminary injunction do not establish that these obligations have disappeared.
For an interstate carrier or owner-operator, the practical checklist is:
- Confirm whether the vehicle falls within Clean Truck Check’s scope. Consider its fuel type, gross vehicle weight rating, registration state, and operation on California public roads.
- Check current CARB requirements and deadlines. Requirements can change separately from the federal litigation, so use current agency guidance rather than relying on headlines about the injunction.
- Complete required reporting, fees, and testing. Do not assume that a vehicle is exempt merely because it is registered outside California.
- Keep testing and repair documentation. Records can matter when a vehicle is inspected or when a failed emissions-control system must be shown to have been repaired.
- Separate diagnostic work from official compliance. A scan that identifies fault codes is useful for repair preparation, but it is not automatically an official CARB test or a certification of legal compliance.
A compatible heavy-duty truck diagnostic scanner may help a fleet identify engine or emissions-system faults before sending a vehicle for repair. Compatibility varies by truck, engine, model year, communications protocol, and the particular regulatory process. Before purchasing or relying on any aftermarket tool, confirm that it works with the vehicle and determine whether CARB accepts that tool or requires a separate testing procedure.
Large operators may also evaluate fleet emissions-compliance services for reporting, inspection preparation, diagnostics, and repair documentation. That category can be useful when a fleet has many vehicles or operates across multiple jurisdictions, but a service provider’s capabilities and current regulatory coverage should be verified rather than assumed.
What are the environmental stakes?
CARB describes its Heavy-Duty Omnibus regulation as a major nitrogen-oxide control measure. CARB estimates reductions of approximately 17.4 tons per day in 2031 and 45.2 tons per day in 2050. Those figures are agency projections and should not be treated as an independently verified outcome of the Partnership or of the lawsuit.
CARB also says that its 2023 amendments gave manufacturers additional compliance flexibility during the 2024–2026 model-year period without changing the program’s overall emissions benefits. That helps explain why the state characterized the Partnership as a practical implementation agreement rather than simply an attempt to impose new requirements without industry input.
For fleets, the wider transition involves more than the court fight. California’s programs address new-vehicle sales, engine nitrogen-oxide emissions, fleet operations, and zero-emission vehicle deployment. The Partnership materials also refer to infrastructure development. Operators considering battery-electric or hydrogen trucks therefore have a separate planning issue: charging, fueling, grid capacity, facility design, and vehicle availability can require substantial lead time even while the legal framework is being contested.
Why did the FTC investigate?
The Partnership also raised competition concerns because four manufacturers—Daimler Truck, International Motors, PACCAR, and Volvo Group—controlled a very large share of the heavy-duty truck market.
In August 2025, the FTC announced that it had closed its investigation after receiving written commitments from the manufacturers. The companies stated that the Partnership was unenforceable and that they would make independent decisions about vehicle sales. The FTC’s action addressed antitrust concerns about coordination among major manufacturers. It did not decide whether California’s requirements were preempted under the Clean Air Act and did not replace the federal court’s injunction.
Who is affected by the lawsuit?
| Group | Why it matters |
|---|---|
| Truck and engine manufacturers | Their certification, product-planning, sales, and compliance decisions are directly tied to the disputed California requirements. |
| CARB and California officials | The injunction limits their ability to use the Clean Truck Partnership, including the related state contract action, while the case proceeds. |
| DOJ and EPA | The federal government is asserting Clean Air Act preemption and challenging the legal effect of California’s waivers. |
| Fleet operators and interstate carriers | They may face uncertainty about future vehicle availability and emissions rules, while still having to comply with separate in-use programs such as Clean Truck Check. |
| Dealers and repair businesses | Changes in model availability, emissions hardware, diagnostic needs, and repair documentation can affect inventory and service procedures. |
What happens next?
The federal case must still address the underlying merits, including the effect of the 2025 congressional resolutions, the scope of Section 209 preemption, and whether California’s Partnership was an unlawful substitute for direct regulation. The state’s contract case in Alameda County is procedurally linked to that dispute; a March 2026 secondary report said the state action had been stayed while the federal case continued.
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That procedural development should not be described as a final victory for either side. Litigation status, appeals, the scope of the injunction, and CARB’s implementation guidance are all subject to change. Manufacturers and fleets should rely on the latest court orders and agency instructions before changing purchasing, certification, testing, or repair practices.
Frequently asked questions
Did the Justice Department win a final judgment against California?
No. The Eastern District of California issued a preliminary injunction on October 31, 2025. It blocks enforcement of the Clean Truck Partnership while the litigation proceeds, but it is not a final merits decision.
Did the court strike down California’s truck-emissions standards?
Not across the board. The order specifically enjoins CARB from implementing or enforcing the Clean Truck Partnership. It does not establish that every California heavy-duty emissions, sales, inspection, or repair requirement is invalid.
Can an out-of-state truck ignore California emissions requirements?
No. CARB says Clean Truck Check covers nearly all diesel and alternative-fuel heavy-duty vehicles above 14,000 pounds that operate on California public roads, including vehicles registered elsewhere. The Partnership injunction does not remove that separate program.
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1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minuteWhat does “federal preemption” mean here?
DOJ’s position is that Clean Air Act Section 209(a) prevents states from enforcing standards for new motor vehicles or engines unless California has a valid Section 209(b) waiver. DOJ and the manufacturers argue that California could not preserve those requirements through a contract after the relevant waivers were invalidated. The ultimate legal answer remains disputed.
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Does a truck diagnostic scanner prove CARB compliance?
No. A scanner may help identify faults and support repairs, but compatibility varies by vehicle, engine, model year, and protocol. An aftermarket scanner is not automatically an official CARB testing device or a legal certification of compliance.
Frequently Asked Questions
Did the Justice Department win a final judgment against California?
No. The Eastern District of California issued a preliminary injunction on October 31, 2025. It blocks enforcement of the Clean Truck Partnership while the litigation proceeds, but it is not a final merits decision.
Did the court strike down California’s truck-emissions standards?
Not across the board. The order specifically enjoins CARB from implementing or enforcing the Clean Truck Partnership. It does not establish that every California heavy-duty emissions, sales, inspection, or repair requirement is invalid.
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No. CARB says Clean Truck Check covers nearly all diesel and alternative-fuel heavy-duty vehicles above 14,000 pounds that operate on California public roads, including vehicles registered elsewhere. The Partnership injunction does not remove that separate program.
What does federal preemption mean in this lawsuit?
DOJ’s position is that Clean Air Act Section 209(a) prevents states from enforcing standards for new motor vehicles or engines unless California has a valid Section 209(b) waiver. DOJ and the manufacturers argue that California could not preserve those requirements through a contract after the relevant waivers were invalidated. The ultimate legal answer remains disputed.
Does a truck diagnostic scanner prove CARB compliance?
No. A scanner may help identify faults and support repairs, but compatibility varies by vehicle, engine, model year, and protocol. An aftermarket scanner is not automatically an official CARB testing device or a legal certification of compliance.
The Bottom Line
Bottom line: DOJ’s case concerns whether California used the Clean Truck Partnership to enforce truck-emissions requirements that federal law allegedly preempts. The October 31, 2025 preliminary injunction blocks enforcement of that Partnership, but it does not erase all California truck rules. Clean Truck Check remains a separate concern for heavy-duty vehicles operating on California roads, including many out-of-state trucks.
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