While the diesel-emissions scandal focus has largely focused on Volkswagen these past few months, remember that both Porsche and Audi are also swept up in the controversy thanks to a shared, non-emissions-compliant 3.0-liter diesel V-6. At the 2016 Detroit auto show, Porsche’s CEO Oliver Blume outlined in general terms his brand’s proposed fix to bring the diesel six into compliance, which was submitted to the EPA and California Air Resources Board (CARB) back in December. According to Reuters, the CEO said the fix was in, but Porsche was simply waiting to see whether the EPA and CARB would accept it.

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Mr. Blume didn’t go into specifics regarding the fix, which would be applied to 2013?2016 model-year Cayenne diesels, but claimed that a hardware change would be required on fewer than half of the 13,000 affected vehicles. Even so, it seems only the catalytic converter would need to be swapped out (in addition to an engine-software reflash) on 2013 and 2014 Cayenne Diesel models. Only an engine-software tweak is needed to bring 2015 and 2016 versions into compliance. Mr. Blume’s remarks did not touch on whether the same fix would apply to the diesel-powered versions of the Cayenne’s close sibling, the Audi Q...