Dozens of transport ministry officials inspected Mitsubishi Motors' offices across Japan on Tuesday after the automaker last week widened a recall to about 1.7 million vehicles.
The inspection of Mitsubishi's Tokyo headquarters and quality-control offices nationwide came after the ministry criticised the firm over the latest expansion of an oil leak recall.
"We are inspecting the company's offices to see whether the quality improvement programme that Mitsubishi submitted to us is appropriate," ministry official Tsuneki Matsuo told AFP.
He added that the inspection, which involves about 40 ministry staff, would include Mitsubishi dealerships in Japan.
Two years ago, Mitsubishi recalled nearly 250,000 vehicles, adding about 300,000 more vehicles to the call back this year, after anonymous tips to the transport ministry prompted officials to order the firm to revisit the glitch.
Last week, the company said it was adding another 1.2 million vehicles to the recall, the latest in a string of safety and quality issues to dent Japan's auto sector.
A faulty engine part could trigger an oil leak and light the oil pressure gauge on the dashboard. In a worst case scenario the engine could seize, the company said, adding that no accidents had been linked to the glitch.
The latest recall prompted a rebuke from transport ministry officials, who said last week they would meet with Mitsubishi officials to press them on the issue, saying the company had not made proper disclosures to the public.
It ordered the firm to report on the status of internal measures taken to prevent a recurrence of the problem, and said it would ask government-chosen experts to probe the recall.
In a statement Tuesday, Mitsubishi said "we will fully cooperate with the on-site inspection and will make steady progress to prevent a repeat".
The transport ministry slap down comes a decade after Mitsubishi admitted to keeping the ministry and public in the dark about tens of thousands of complaints filed by car owners dating back to the late 1970s.
There were some fatal accidents linked to the safety problems.
Bigger rivals Toyota, Nissan and Honda have recalled millions of vehicles in recent years, dealing a blow to their safety and quality image.