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Person using equipment to test emissions from a car exhaust.

Emissions generated from gasoline and diesel powered vehicles are one of the greatest sources of air pollution in Minnesota. Equipment to reduce emissions are included on most vehicles. Federal law prohibits removal, alteration or otherwise tampering with a vehicle’s pollution control equipment.

What is tampering?

Tampering is removing, disconnecting, altering, bypassing or rendering ineffective any pollution control equipment installed in a motor vehicle. Tampering with a vehicle emissions control system is illegal and can negatively affect vehicle performance, void warranties, and contribute to air pollution. 

State law prohibits renting, leasing, offering for sale, or transferring ownership of a motor vehicle unless all air pollution control systems are in place and in operating condition. Even vehicles sold “as is” or without warranty must comply with anti-tampering laws. Tampering with, or selling a vehicle that has been tampered with, may result in monetary penalties. The components of a vehicle emission control system that can be tampered with include, but are not limited to:

  • catalytic converter
  • air injection system
  • evaporative emission system
  • exhaust gas recirculation (egr)
  • system fuel inlet restrictor
  • oxygen sensor positive
  • crankcase ventilation (PCV)
  • computer command controls
  • thermostatic air intake system
  • diesel particulate filter

Common auto dealer questions

Should I take a tampered vehicle as a customer trade-in for a new vehicle?
No. The trade-in transaction is considered a sale, and this act would violate the anti-tampering law. If a customer offers you a tampered vehicle in trade, you should tell them, for their own protection, that the tampered emissions systems must be repaired prior to accepting the vehicle. Alternatively, you may offer to repair the vehicle, if you have the ability to do the necessary repairs, and work out the repair costs as part of the trade-in agreement.

How can I protect myself from a customer falsely accusing me of selling a tampered vehicle?
To protect yourself from the ramifications of selling, or being accused of selling a tampered vehicle, you may want to develop a checklist of emission control systems that you and the consumer can review prior to vehicle purchase.

There are at least three companies in the U.S. that produce manuals containing emission control tables for most makes and models of foreign and domestic vehicles. These manuals are good resources for repair technicians and vehicle dealers concerned about the federal and state anti-tampering laws.

May I sell a tampered vehicle to a salvage dealer for parts?
Yes, if the dealer is a licensed salvage dealer. Vehicles with salvage certificates of title are exempt from the provisions on the anti-tampering law. Be sure that the dealer to whom you sell the tampered vehicle has a salvage dealer license and that they intend to obtain a salvage certificate of title for the vehicle; it is a good idea to get this in writing. Following the above procedure will make it clear that you intend to comply with the anti-tampering law.

Common auto mechanic questions

Can I work on a vehicle which was previously tampered with?
Yes. However, if you are replacing a part that is not the proper part for that vehicle and emission system, then you are required to put the proper parts back on the vehicle. If you perform any work on any part of the vehicle which has been previously tampered with, you must perform the correct repair or not do it at all in order to not be liable for tampering. This is true regardless of the age or mileage on the vehicle, and applies to any motor vehicle which was designed to meet federal emissions standards. 

Do mechanics have to use replacement parts that are made by the manufacturer?
No. You may also use rebuilt parts, or equipment made by independent aftermarket parts manufacturers. Replacement parts must be equivalent in design and function to the parts that were originally on the vehicle when it was certified. They must not have a negative effect on emission control. To be certain you're using acceptable replacement parts, get a written statement from the parts manufacturer saying that the replacement part conforms in design and function with the original part.

Can I remove a converter from a vehicle that is used only for off-road driving?
No. The tampering prohibition applies to "motor vehicles", which are defined as "any vehicle, including mobile homes and recreational vehicles, that is propelled or drawn by power other than muscular power or power collected from overhead electric trolley wires." A light-duty vehicle manufacturer certifies an engine chassis configuration as meeting the applicable emissions standards for motor vehicles manufactured in a given model year, and it is not legal for anyone to "de-certify" a motor vehicle for off-road use. 

Can I replace a catalytic converter with a converter replacement pipe?
No. Under state and federal law, catalytic converters may not be removed and replaced with "converter replacement pipes" by any person. The 1990 Clean Air Act Amendments even prohibit private individuals from installing converter replacement pipes on their own vehicles. It is also a prohibited act to replace an existing "converter replacement pipe" on a vehicle that has already been tampered with. 

If a converter-equipped vehicle is brought to a shop with a converter already removed by the owner, is it tampering to install a section of pipe in the space left vacant by the converter's removal?
Yes. If a repair facility completes, assists, or participates in any way of tampering begun by someone else, it has also violated state and federal tampering laws. 

Stay in compliance

  • Before accepting a vehicle as a trade-in, verify that it meets all federal and state emission system tampering laws
  • Before offering a vehicle for sale, ensure that the emissions control system is fully functional and has not been tampered with
  • If you also service vehicles, perform all work on emission controls according to manufacturer specifications and Do not tamper with vehicle emission controls
  • Do not advise customers on how to tamper with their vehicle emission controls 
  • Do not work on tampered emission controls unless repairing them to their original condition - otherwise you can be held personally liable