Earlier examples of the EA 189 diesel engine used a lean NOx trap to reduce the harmful material coming from the tailpipe. According to experts in the Automotive News report, a software update might allow the engines to achieve compliance, but that could affect fuel economy. VW already tried this route once before the scandal came to light, but tests by the California Air Resources Board still showed the figures were too high.
Later, some of the 2.0 TDI engines began using Selective Catalytic Reduction that reduced NOx by injecting a urea solution into the exhaust stream. According to Automotive News, a software update for this equipment might increase the amount of the substance used. Not only would that mean topping up the fluid more often, but there still could be some reduction in fuel economy. But, since the 2-liter, 4-cylinder TDI engine that sits inside the diesel vehicles first mentioned as being affected by the issue in the US don't have a urea treatment system, VW would need to install them into these cars.
VW still hasn't officially outlined its solution (or solutions) to the emissions issue but is expected to soon. The automaker's long-term evasion of regulations with these diesel engines pumped vast quantities of additional NOx into the air. The substance is known to be linked with smog and acid rain. The US Department of Justice is already beginning an investigation into the company, and politicians are pushing for harsh punishments.