An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Verified Technologies for SmartWay and Clean Diesel

Requirements for In-Use Emissions Testing for Clean Diesel Technology

In-use testing is used to confirm the field performance of products that are on the List of Verified Technologies.

Each retrofit technology manufacturer is responsible for conducting in-use testing as part of the Verification Process for Clean Diesel Technology.

In-use testing that fails will result in:
  • Loss of emission credits for states that used the verified technology to generate them for their state implementation plans (SIP); and
  • Removal from the List of Verified Technologies.
Follow these steps for in-use testing:

1. Confirm with EPA that in-use testing is required.

In-use testing begins:
•    After at least 500 units of a verified product have been introduced into commerce; and
•    Within one month of availability of engines for applicable phase, or as arranged with EPA.

Test Phase I Test units are aged to 25% of the designated durability testing period
Test Phase II Test units are aged to 75% of the designated durability testing period

2. Review system requirements for test procedures.

Identical, rigorous, and repeatable test procedures must be conducted on the unmodified engine and the engine with the retrofit applied.

Acceptable Test Systems Examples of Unacceptable Test Systems
  • An engine dynamometer;
  • A chassis dynamometer; or
  • A mobile emissions detection system.
  • A chassis dynamometer for the test on the unmodified engine; and
  • A mobile emissions detection system for the test on the engine with the retrofit applied.

3. Determine test method and obtain approval.

The test method depends on the retrofit product.

Choose the applicable method below.

After-Treatment Technologies

Control Strategy Upgrade Technologies

Examples: Catalysts, particulate filters and other removable technologies for testing purposes

For successful testing, the manufacturer must:

  • Keep records and fleet applications to have devices.
  • When a CCV is a part of the verified technology, CCV systems may be required for in-use testing and engine inspections are required.

Example: Replacement of mechanical fuel control with electronic fuel control

For successful testing, the manufacturer must:

  • Be sure to set aside and test enough unmodified engines.
  • Account for inevitable loss of engines over time due to accidents, fires, and other unforeseen incidents.

4. Review Sampling Plan requirements for unmodified test engines.

The unmodified test engines sample should:

  1. Represent the distribution of the technology across various applications;
  2. Be selected randomly;
  3. Include a mixture of end-user entities and mileage accumulations;
  4. Include a description of any unscheduled maintenance which might affect the emission results, along with the expected emissions effect.

5. Determine test cycles.

Required test cycles and protocols for each type of test are fairly well defined.

Use the table below as a guide.

Type of Test Corresponding Test Cycle
Highway engine dynamometer test Federal Test Procedure (FTP) transient test cycle
Chassis dynamometer test Urban Dynamometer Driving Schedule (UDDS) test cycle; or other pre-approved test cycle
Non-road engines tested using the engine dynamometer Applicable non-road FTP test cycle
Tests using mobile emissions sampling systems Conditions which reflect normal operation for the engine/truck/equipment being tested

For more information on test cycles, see: Dynamometer Drive Schedules

6. Conduct testing.

Initial testing is conducted on four units of the verified technology for both Phase I and Phase II with mileage or hour accumulations for the applicable phase (25% for Phase I and 75% for Phase II).

7. Determine success or failure.

Determine success or failure for initial testing based on the following:


(Reduces emissions of target pollutant by at least 75%)

Testing is complete if:

  • Four units pass initial testing of Phase I, and
  • Four units pass initial testing of Phase II.


(does NOT reduce emissions of target pollutant by at least 75%)

Each failed test:
  • Must be attributable to the product (and not to maintenance or another problem)
  • Requires two or more additional tests that must achieve 70% reduction in emissions, up to a total of ten.
  • May result in an extension of in-use testing, if requested by the manufacturer.
If 70% reduction is achieved in additional testing:
  • In-use testing ceases and manufacturer has achieved success.
If 70% reduction is NOT achieved in ten tests:
  • Dynamometer testing would be required; and
  • Sampling Plan would be repeated.

Retrofit technologies that fail dynamometer testing will be removed from the List of Verified Technology.

8. Report test results to EPA.

Test results:
  • Must be submitted within three months of the completion of testing;
  • Are much easier to process when provided electronically; and
  • May require corrective action if EPA determines a strong bias in testing.