Volkswagen is unsure if it will bring its diesel engines back to the United States after last year’s emissions scandal.

While speaking with the Wall Street Journal earlier in the week, the head of Volkswagen AG North America, Hinrich Woebcken, said that due to harsher emissions regulations in the United States, it is become more difficult to produce diesel engines capable of passing tests.

Because of this, the German company is on a “product by product and package by package” basis, evaluating whether it is worth the investment of returning its diesel models to the U.S. market.

In the meantime, the firm is focusing on sales of its petrol-powered vehicles as well as those of its hybrid models and future all-electric cars.

Volkswagen’s diesel woes in the U.S. are compounded by the fact that it has still yet to receive approval for certain diesel engines found to have illegally cheated emissions tests. This comes a full 12 months after the scandal first broke and after the company agreed to pay almost $15 billion to settle emissions-cheating claims with national consumers and regulators.

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