Tampering and Aftermarket Defeat Devices

What is tampering and why is it important?

Under the Clean Air Act (CAA), tampering with or defeating emission controls is prohibited.  In addition, it is a violation of the Clean Air Act “for any person to manufacture or sell, or offer to sell, or install, any part or component intended for use with, or as part of, any motor vehicle or motor vehicle engine, where a principal effect of the part or component is to bypass, defeat, or render inoperative any device or element of design installed on or in a motor vehicle or motor vehicle engine in compliance with regulations under [Title II of the CAA], and where the person knows or should know that such part or component is being offered for sale or installed for such use or put to such use.”

Congress’ purpose behind these rules was to protect public health as increased emissions are linked to:

Premature death in people with heart or lung disease
– Nonfatal heart attacks
– Irregular heartbeat
– Aggravated asthma
– Decreased lung function
– Increased respiratory symptoms, such as irritation of the airways, coughing or difficulty breathing


We have come a long way in reducing emissions from diesel engines, but tampering can take away all of the progress that has been made by removing the emission controls that have helped to significantly reduce diesel emissions.  A “full delete” of the emission controls on a modern diesel pickup truck can cause it to emit as much harmful pollution as 300 trucks with fully functional emission controls.

In addition, recent EPA investigations have found that tampering is rather widespread with controls on over 500,000 diesel pickup trucks or about 13% of those registered that were originally certified with emission controls.  The excess NOx emissions from these vehicles is the equivalent of adding 9 million trucks to our roads.  This data does not include the potential impacts of tampering heavy-duty trucks, non-road equipment, and agricultural equipment.

What can I do to help combat tampering?

Report Suspected Tampering

Suspected tampering can be reported either by e-mail to tampering@epa.gov or through the suspected violation reporting form.  Links can be found below:

Outreach Materials

Learn More

There are a number of great resources for learning more about this issue.  Clean Air Northeast has an excellent tampering page with a comprehensive list of information, links, and resources.  Also linked is the EPA National Compliance Initiative page with additional information.

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