The two sides agreed to uphold principles of "globalisation, localisation, industrial co-operation and transparency", and welcomed the expansion plans for overseas production announced by the five big Japanese car firms. But the figures for increased production in America and for US sales in Japan were not subject to trade laws.
The deal was received warmly in Tokyo on the day when more than 2,000 companies held their annual meetings.
Reactions all made much of the fact that the figures included in the accord were voluntary, and that no concrete promises had been made by the Japanese government.
The overnight news lifted the Nikkei 261 points in the first 15 minutes of trading, although the index slipped later in the day.
"We want to repeat that these plans must not be ones that will be restricted, forced, or involve participation by the government, and must not be targeted by any laws in either nation," Cabinet Secretary Kozo Watanabe said.
All that the Japanese side agreed to unambiguously was a "review" of the market for replacement parts and to write to car dealers to affirm their right to sell foreign cars.
Analysts predicted that the agreement would lead to increased production of Japanese cars in America, and greater use of US-made parts.
But given the weakness of the dollar, the Japanese firms have already begun to transfer production off-shore.
If anything, the agreement gives them an excuse for scaling down uncompetitive domestic factories.
"The accord reached was good news for both sides," said Takashi Kawamura, of the New Japan Economic Research Centre. "But the fact that the agreement was based on production plans by Japanese manufacturers shows that it is unresolved. Those plans are not new at all." ."