Jump to main content or area navigation.

Contact Us

National Clean Diesel Campaign (NCDC)

Working Together for Cleaner Air

In-use Testing

Retrofit Technology In-use Testing Requirements

As retrofit technologies are introduced into the market and as states begin to rely on these technologies to improve their air quality and generate credits for their state implementation plans (SIP), it becomes increasingly important to verify the field performance of the products. The following in-use testing requirements are part of the OTAQ Verification Process and the responsibility of each retrofit manufacturer. Failure to prove acceptable in-use performance will result in loss of emission credits and removal from the Verified Technology List.


In-use testing is not required to begin until at least 500 units of a verified product have been introduced into commerce. Technology manufacturers will inform EPA, as part of their verification application, when they believe they will have introduced 500 units. There are two phases to the in-use testing program. In each phase, units in normal field operation must have reached a certain age prior to being tested. All testing is the responsibility of the retrofit technology manufacturer and shall begin within one month of an adequate number of engines becoming available for each phase, unless a previous agreement has been made with EPA.

  • Phase 1 - Test units aged to 25% of the designated durability testing period.
  • Phase 2 - Test units aged to 75% of the designated durability testing period.

Top of page

In-Use Test Methods

The actual test method to be used will depend upon the retrofit product. For all products it is important that identical, rigorous, repeatable test procedures be used in unmodified engine and with-retrofit-technology testing. For example, using a chassis dynamometer for the unmodified engine test and a mobile emissions detection system for the with-retrofit-technology test would be unacceptable. One must be able to compare the test results directly. It is also important to have OTAQ pre-approval of the in-use test method to be used.

  • After-Treatment Technologies (Catalysts, particulate filters and other technologies that may be removed for testing purposes.)

    Once the sales and durability testing period requirements are met, after-treatment technologies are to be tested for in-use performance. The retrofit manufacturer is responsible for testing the technology using a system such as an engine dynamometer, chassis dynamometer, or a mobile emissions detection system for tests with the device installed and unmodified engine tests. All pollutants shall be measured during the in-use testing.

  • Control Strategy Upgrade Technologies (Replacement of mechanical fuel control with electronic fuel control is an example.)

    Prior to installation of the retrofit technology, manufacturers of upgrade technologies must conduct unmodified engine tests; later these same engines will be tested again after some period of normal, in-use operation. An engine dynamometer, a chassis dynamometer, or a suitable mobile emissions detection system may be used for this testing. All pollutants shall be measured during the in-use testing.

    One key to a successful in-use program for these types of retrofit technologies will be to choose and test enough engines. Unmodified engine tests must be completed on a population of engines large enough to reflect the inevitable loss (accidents, fires, etc.) of some engines over time so that there will be an adequate set of engines to draw from for required in-use testing, even if they run to their most extensive number. These requirements demand caution and careful planning on the part of upgrade technology manufacturer as one cannot “go back” and obtain suitable unmodified engine tests.

  • Top of page

  • Sampling Plan (This section applies to after-treatment technologies and control strategy upgrade technologies.)

    The unmodified tested engines sample should be representative of the distribution of the technology across the various applications and uses to which it has been applied. Engines to be tested are to be selected randomly and the sample should include a mix of end-user entities as well as mileage accumulations. Additionally, manufacturers must include, along with the test results, a description of any unscheduled maintenance which may affect the emission results, and its expected emissions effect.

  • Test Cycles

    While the retrofit manufacturer may propose which type of emissions testing equipment to use for in-use testing, the required test cycles and protocols for each of type of equipment are generally well defined. Highway engine dynamometer tests must be conducted over the Federal Test Procedure (FTP) transient test cycles. The Urban Dynamometer Driving Schedule (UDDS) test cycle, or other pre-approved test cycle, is required for chassis dynamometer tests. Non-road engines, that are tested using the engine dynamometer, will be tested using the applicable non-road FTP test cycle. All tests using mobile emissions sampling systems must be conducted over conditions which reflect normal operation for the engine/truck/equipment being tested.

  • Testing

    Initially, four engines must be selected for in-use testing. The engines must have mileage or hour accumulations greater than 25% (for Phase I) or 75% (for Phase II) of the minimum durability testing periods defined in the table to be developed.

    At least four units must be tested: if all four pass, testing is complete. A unit passes if testing shows that it reduces emissions of the target pollutants by at least 75 percent of its original OTAQ Verification Process reduction. For testing beyond the initial four units, a 70 percent pass rate must be achieved. For each failed test, for which the cause can be attributed to the product and not to maintenance or other engine related problems, two or more additional units will be evaluated, up to a total of ten.

  • Failures

    If the 70 percent success rate is not achieved in ten tests, then dynamometer testing would be required. The manufacturer may request an extension of the in-use testing program in order to achieve a 70 percent success rate in lieu of dynamometer testing. EPA would then determine at what point during the extension, dynamometer testing should be performed. If the manufacturer demonstrates a 70% success rate during the extension, in-use testing would cease. In the event dynamometer testing is required, the sampling plan would be repeated. Retrofit technologies that fail dynamometer testing will be removed from the Verified Technology List.

  • Test Results

    Test results for all phases are to be submitted to EPA using the format provided. Note that test results provided electronically are normally much easier to process than paper submissions. The results will be submitted to EPA within three months of the completion of testing. Should EPA determine strong bias in testing, EPA may require corrective action, i.e., additional in-use testing of non-represented engines.

Top of page

For questions, technical assistance, or more information: Contact Us

Jump to main content.