Vehicle Emissions Inspection and Maintenance (I/M): Information for State and Local I/M Agencies
On this page:
- General Information
- Policy and Technical Guidance
- On-Board Diagnostic (OBD) Resources
- Other I/M Testing Resources
- Auditing Resources
- Additional Technical Resources
Vehicle inspection and maintenance (I/M) programs help improve air quality by identifying cars and trucks with high emissions and that may need repairs. Owners or operators of vehicles with high emissions are notified to make any repairs so that emissions are within legal limits. The 1990 Amendments to the Clean Air Act (CAA) established I/M requirements for several areas across the country. This page contains useful resources for State and Local jurisdictions operating Vehicle I/M programs.
General Information
- Overview of Vehicle Inspection and Maintenance (I/M) Programs (pdf) (October 2021, EPA-420-F-21-067)
This document provides information on I/M programs such as where I/M programs are required and an overview of I/M testing. - Overview of Vehicle Repair and Replacement Assistance Programs (pdf) (May 2023, EPA-420-F-23-013)
This document explores how some state and local I/M programs include provisions for vehicle repair or replacement assistance programs for low-income motorists. - OBD Clearinghouse: Weber State University's Center for Automotive Science and Technology
Learn the latest on state and local OBD I/M implementation, technician training opportunities and state outreach materials.
Policy and Technical Guidance
EPA has developed policy and technical guidance on several topics related to I/M program implementation, annual reporting, performance standard modeling, biennial program evaluation, and more that may be relevant for State and Local I/M Agencies available on the Vehicle Emissions Inspection and Maintenance (I/M): Policy and Technical Guidance page.
On-Board Diagnostic (OBD) Resources
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Best Practices for Addressing OBD Readiness in IM Testing of Diesel Vehicles Under 14,000 Pounds Gross Vehicle Weight Rating Memo (pdf)
This memorandum summarizes the findings of a technical forum investigating the best practices for addressing on-board diagnostic (OBD) readiness-related issues that may be encountered during the I/M testing of light- to medium-duty diesel vehicles. The accompanying document identifies best practices as recommended by government, industry, and trade association stakeholders. This document is provided as a courtesy by EPA to interested states to help those who choose to test these vehicles, but should not be construed as an endorsement of such testing, nor as official EPA guidance on the matter. - OBD Readiness Testability Issues (pdf) (June 2012, EPA-420-B-12-044)
This memo and accompanying document update the I/M OBD Vehicles Readiness Exception List (pdf) (January 2008, EPA420-F-08-009) to list specific vehicle makes and models with OBD readiness issues and make suggestions for how I/M programs can improve operational performance by addressing monitor readiness. - On-Board Diagnostics (OBD) Inspection and Maintenance (I/M) Program Implementation for Flexible Fuel Vehicles (FFVs) (pdf) (May 2007, EPA-420-B-07-022)
This document is to provide additional information on the inspection process of alternative fueled vehicles equipped with On-Board Diagnostic (OBD) systems. Specifically, this document provides additional technical information and impacts on the OBD system monitoring capability when flexible fuel vehicles (FFVs) are operated using alternative fuel. - Performing On-Board Diagnostic System Checks as Part of a Vehicle Inspection and Maintenance Program (pdf) (June 2001, EPA420-R-01-015)
The guidance document contains EPA's recommendations regarding the effective implementation of OBD-I/M checks in I/M programs. The recommendations contained in this guidance are consistent with EPA's amended OBD-I/M requirements, published April 5, 2001 (66 FR 18156).- Improving I/M Performance and OBD Monitor Readiness Memo (pdf) This memorandum updates the list of vehicles in the June 2001 guidance that exhibit OBD monitor related readiness issues.
Other I/M Testing Resources
- Acceleration Simulation Mode Test Procedures, Emission Standards, Quality Control Requirements, and Equipment Specifications Final Technical Guidance (pdf) (July 2004, EPA420-B-04-011)
This guidance outlines the Acceleration Simulation Mode (ASM) test procedure. - IM240 & Evap Technical Guidance (pdf) (April 2000, EPA420-R-00-007)
This document outlines the IM240 test procedure and supersedes the August 1998 version of the EPA “IM240 & Evap Technical Guidance”. The below spreadsheet and sample calculations are referenced by the guidance. - The IM240 Transient I/M Dynamometer Driving Schedule and The Composite I/M Test Procedure (pdf) (January 1991, EPA-AA-TSS-91-1)
This document provides descriptive information about the IM240 driving schedule test and provides information on EPA’s Composite I/M Test Procedure (CITP).
Auditing Resources
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EPA Equipment Audit Guidelines (pdf)
These guidelines should be used by states as a comprehensive tool for auditing I/M tailpipe testing equipment. The below forms are to be used with these guidelines. - Instructions for Requesting a Testing Exemption for Light-duty Vehicles (pdf) (June 2022, EPA-420-B-22-028)
This document provides instructions to state and/or local government agencies, which have enforcement authority over their I/M programs, on how to request exemptions from tampering prohibitions for vehicles used in covert audits.
Additional Technical Resources
- Calculation of I/M Waiver Adjusted for CPI (pdf) (December 1999, EPA420-B-99-011)
This document describes the methodology that states should use to determine the minimum repair expenditure limit for waiver under 40 CFR 51.360 of the I/M regulations. Agencies may also use the Consumer Price Index (CPI) Inflation Calculator developed by the U.S. Bureau of Labor Statistics to determine waiver threshold amounts. - Model Year Exemption Policy (pdf)(December 1999, EPA420-S-99-007)
This document contains a series of questions and answers on exempting vehicle model years from I/M testing consistent with the I/M regulations. This document is relevant for any I/M analyses completed with the latest version of EPA’s MOVES model. - Remote Sensing: A Supplemental Tool for Vehicle Emission Control (pdf) (August 1993, EPA420-F-92-017)
A fact sheet looking at the role of remote sensing as a tool to evaluate vehicle emissions.