Audi will revise, document, and resubmit for approval certain parameters of the engine-management software used in the 3.0L V-6 TDI diesel engine the U.S. Environmental Protection Agency has claimed violates clean-air laws, the automaker has announced.

The updated software will be installed in affected Audi, Porsche, and Volkswagen vehicles as soon as it is approved by authorities, including the California Air Resources Board (CARB), Audi announced.

The announcement stems from discussions focused on a Nov. 2 notice of violation, in which the EPA informed Audi it found undisclosed emissions control devices used to defeat U.S. diesel emissions laws.

Audi has confirmed that three so-called Auxiliary Emissions Control Devices (AECDs) were not declared when the automaker submitted the vehicles for approval. One of the AECDs relates to the temperature conditioning of the exhaust‑gas cleaning system. The other two AECDs are for the avoidance of deposits on the ad-blue metering valve and of HC poisoning of the SCR catalyst with unburnt hydrocarbons. One of them is regarded as a defeat device according to applicable U.S. law. Specifically, this is the software for the temperature conditioning of the exhaust-gas cleaning system.

Audi has agreed with the environmental authorities on further steps of cooperation in which the concrete measures to be taken will be specified. The company has committed to continue cooperating transparently and fully. The focus will be on finding quick, uncomplicated and customer-friendly solutions. The voluntary sales stop for models with the V6 TDI diesel engine, which the three affected Group brands had provisionally decided upon, has been extended until further notice.

This engine was developed by Audi and is used in the A6, A7, A8, Q5 and Q7 from the 2009 model year onwards. Volkswagen uses the engine in the Touareg and Porsche has used it in the Cayenne since model year 2013.

Read Audi's full statement here.