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California Approves HD NOx Omnibus Rule; MEMA Advocates for Suppliers

Date: September 8, 2020

On August 27, the California Air Resources Board (CARB) approved its heavy-duty (HD) NOx Omnibus rulemaking that sets stringent new HD NOx standards, extends emissions warranty requirements and full useful life (FUL), and changes in-use testing methodologies.  CARB initiated, nearly seven years ago, the Low NOx Demonstration Program with Southwest Research Institute (SwRI) in collaboration with U.S. EPA, to demonstrate the feasibility of achieving 90 percent reduction of NOx emissions from current HD engines. Within those seven years, CARB collaborated with industry stakeholders - including technology suppliers - early in the regulatory development process. Suppliers provided significant technology advancements that support important emissions reductions from HD vehicles since California last revised the HD NOx standards.

MEMA submitted comments and provided testimony to CARB indicating that the trade association strongly supports the CARB’s goals of the Omnibus rulemaking outlined in the proposal. HD vehicle suppliers, which MEMA represents through its HDMA division, support a holistic HD NOx emissions reduction strategy and encourage stringent new standards that support implementation of the best available cost-effective, emissions reduction technologies. Maintaining stringency in the HD NOx standards is necessary to continue strengthening supplier manufacturing sector jobs − the largest sector of manufacturing jobs in the U.S. − and driving a global technology leadership position for U.S. manufacturers. MEMA also continues to encourage CARB and U.S. EPA to coordinate on their HD low NOx programs and to work to harmonize the programs as closely as possible.

Specifically, MEMA advocated for California to adopt stringent, feasible, cost-efficient HD NOx standards of 0.05 g/bhp-hr for MYs 2024-2026 and 0.02 g/bhp-hr for MY2027 and subsequent years. MEMA successfully negotiated significantly scaled back and phased-in FUL and emissions warranty requirements. MEMA also successfully advocated CARB limit the double counting of the HD ZEV credits allowed to count toward HD NOx compliance (credits sunset after 2026 instead of after 2030); CARB removed the optional 50-state program which allowed OEMs to certify engines nationwide to 0.1 g/bhp-hr in 2024-2026; and CARB will conduct a study on emissions component wear and impact on costs as a result of the lengthened warranty. MEMA and HDMA will now turn to working with U.S. EPA to provide a HD NOx national program.

MEMA Advocacy on CARB’s HD NOx Omnibus


NOx Standards

MEMA Advocacy Objective:
CARB establish HD NOx standards that promote the best-available, cost-effective technologies. Specifically, a HD NOx 0.02 g/bhp-hr standard in 2027.

Result: CARB established a stringent 90 percent reduction of the current HD NOx standard, setting the standard at 0.02 g/bhp-hr starting in 2027 along with stringent low-load certification cycle standard and idling standard.




NOx Idling












2027 and







Emissions Warranty and Full Useful Life

MEMA Advocacy Objective:
CARB scale back and phase in its proposed extended FUL and emissions warranty requirements for Class 4-8 vehicles. MEMA also requested CARB study emissions parts to help suppliers mitigate increased costs associated with supplier durability development meeting the increased warranty requirements.

1. CARB significantly scaled back and phased-in its FUL and emissions warranty requirements.
(e.g. FUL was scaled back from 1 million miles in 2027 to 800,000 in 2031 and emissions warranty requirements from 800,000 in 2027 to 600,000 in 2031 (for Class 8).
2. CARB has agreed to study over 9 months the impact on the longer warranty requirements, its costs, how they will impact first and second vehicle owners, etc. U.S. EPA will join the study.

Disallow Credits for HD ZEVS in the Omnibus

MEMA Advocacy Objective:
Prevent double counting of HD ZEV credits allowing vehicle manufacturers to generate credits for the HD NOx Omnibus program with the same HD ZEVs that are being used to comply with California’s Advanced Clean Trucks (ACT) rule.

CARB limited credits allowed to be generated from HD ZEVs to sunset after 2026 (originally proposed to sunset after 2030).


Revisions to the Optional 50-State FTP Standard

MEMA Advocacy Objective:
CARB revise the FTP standard for its optional 50 state program to 0.08 g/bhp-hr from the proposed 0.01 g/bhp-hr. CARB provides an option for vehicle manufacturers to certify MYs 2024–2026 engines to a less stringent standard than CARB’s 0.05 g/bhp-hr standard if they meet that standard on a nationwide basis.

The optional 50-state program was removed from the rule.

You can read the full comments here.

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