Tampering of emissions control systems is prohibited


Who is affected by this notice?

Vehicle owners, operators, automotive/diesel technicians and repair facilities, fleet managers, car and truck dealers, and auto/truck parts retailers.

Why is CDPHE issuing this notice?

It is illegal under state and federal law to tamper with the emissions system of any vehicle. All vehicles (gasoline-or-diesel-powered, and light-or-heavy-duty) are subject to the regulation.

What is the definition of tampering?

Tampering is defined as the disconnecting, deactivating, removing or rendering inoperable any emission control device or element of design installed or engineered by the manufacturer on your vehicle, and is prohibited pursuant to CRS 42-4-314.

All vehicles certified for sale in the United States by U.S. EPA or the California Air Resources Board (CARB) have emission control systems that monitor and regulate the engine operations and exhaust gases to maintain air pollutants at strict levels. Tampering with these devices is illegal: it causes excess pollution, and may cause damage to other emissions control devices on your vehicle.

If you remove, disconnect, detach, deactivate, alter, modify, reprogram, or reduce the effectiveness of any emission control device installed by the manufacturer, or use less-effective replacement parts, then you are committing the act of tampering. This includes reprogramming or “re-flashing” the vehicle’s computer, or installing performance chips to circumvent or “defeat” factory settings, or to produce excessive exhaust smoke (diesel trucks). This also includes modifications such as installing an aftermarket exhaust system (pre-catalyst), or installing larger capacity turbocharger and/or turbo waste-gate modifications.

Tampering with a vehicle will also void its warranty.

Any person other than a manufacturer or dealer who violates this section, or any person who violates the Clean Air Act (CAA § 203(a)(3)(B)), shall be subject to a civil penalty of not more than $3,750 per violation. Any manufacturer or dealer who violates this section shall be subject to a civil penalty of not more than $37,500 per violation.

What is CDPHE doing?

CDPHE is reaching out to vehicle owners, fleet managers, vehicle dealers and enforcement agencies to clarify the tampering prohibition. 

What should I do?

Here is a general (but not complete) list of things to check to ensure compliance:

  • Do not remove, disconnect, detach, deactivate, alter, modify, reprogram or in any way render any emission control device or element of design inoperable or less effective than originally designed.
  • Do not sell, lease, or offer for sale or lease any vehicle with a tampered emissions system.
  • Do not purchase a tampered vehicle from any person, dealer, or auto auction.
  • Do not install any non-compliant emission control devices on your vehicle or engine.
  • Use only emissions control systems replacement parts that are approved by U.S. EPA or CARB.

Additional information: 

For additional information on vehicle tampering, contact the CDPHE Emissions Technical Center 888-861-2646

Or send an email:

Gasoline-powered vehicles:

Diesel-powered vehicles: