US EPA finds illegal emission strategy in Volkswagen 3 L engines

2 November 2015

The US Environmental Protection Agency (EPA) issued today a Notice of Violation (NOV) to the Volkswagen Group alleging that several model year 2014-2016 cars and SUVs powered by the 3 liter Volkswagen diesel engine are equipped with software designed to defeat regulatory emission testing, which represents an illegal emission “defeat device” under the US Clean Air Act. An In-Use Compliance letter was also issued by the California Air Resources Board (ARB).

The vehicles named in the NOV include the 2014 VW Touareg, the 2015 Porsche Cayenne, and the 2016 Audi A6 Quattro, A7 Quattro, A8, A8L and Q5. When the Volkswagen emission scandal broke out in September, the company admitted using illegal dual calibration software, but only in vehicles powered by 2 liter diesel engines. While most of the affected 2 liter engines used NOx adsorber-based aftertreatment, the vehicles with the 3 liter engines were equipped with urea-SCR NOx control systems.

The dual calibration software in VW 3 liter diesel engines was found through emission testing performed by the EPA’s National Vehicle and Fuel Emissions Laboratory, California ARB’s Hagen-Smit Laboratory, and Environment Canada’s River Road Laboratory.

In the NOV, the EPA explains some of the technical details discovered during the testing. When the software determines the vehicle has begun the FTP-75 test cycle, it directs the vehicle to employ a low NOx “temperature conditioning” mode. A status bit in the software indicates that a temperature conditioning mode is active. In this low NOx temperature conditioning mode, the engine operates under a set of parameters—including injection timing, EGR rate and common rail fuel pressure—designed to produce low engine-out NOx and high exhaust temperatures. The high exhaust temperatures ensure early light-off of the SCR catalyst after the cold start and improve the SCR NOx conversion efficiency throughout the duration of the FTP-75 test. In this low NOx mode, the combination of low engine-out NOx and improved catalyst performance results in tailpipe NOx emissions that are below the applicable emission standard.

The software employs a “timer” that coincides with the low NOx temperature conditioning mode. At exactly one second after the completion of the initial phases of the FTP-75 test (1,370 s, which is when the vehicle would normally be turned of), the software directs the vehicle to cease low NOx temperature conditioning mode. The “temperature conditioning” status bit switches to zero, and a second status bit indicates the activation of “transition to normal mode”. In this “normal mode”, the emission control system is immediately less effective. Compared to the low NOx temperature conditioning mode, the vehicle employs a different injection timing, EGR rate, and common rail fuel pressure. This yields higher levels of NOx from the engine and reduced exhaust temperatures.

When the vehicle starts under conditions that the software determines are not the beginning of the FTP-75, the vehicle does not use the low NOx temperature conditioning mode at all. Instead, the emission control parameters are set consistent with the “normal mode”.

In summary, as soon as the vehicle senses that it is not being tested, it uses normal mode. In the normal mode, tailpipe NOx emissions are up to 9 times the applicable NOx standard levels, depending on model type and type of drive cycle (city / highway).

The EPA’s investigation into this matter is continuing—noted the agency—and the EPA may find additional violations as the investigation continues. The California ARB said it is very disappointed with this development as VW was alerted on September 25, 2015 that ARB would be immediately conducting defeat device testing.

Source: US EPA | California ARB