WASHINGTON—Two Japanese autoparts suppliers will pay fines of more than half a billion dollars over a price-fixing conspiracy in the sale of parts to U.S. automakers.

Yazaki Corp. will pay a US$470-million fine, the second-largest criminal fine ever obtained for an antitrust violation.

DENSO Corp., the second company, will pay a $78-million fine.

Four Yazaki executives will also serve up to two years in U.S. prison and pay $20,000 in fines as part of plea bargain.

Prosecutors say Yazakis bid rigging included automotive wire harnesses that direct and control a vehicles electronic components, instrument panel clusters that drivers use on the dashboard to gauge vehicle performance and fuel senders that measure the amount of gas in the tank.

DENSOs alleged price-fixing involved electronic control units that control electronic systems and heater control panels.

The pleas are part of an ongoing investigation—the largest ever in the Justice Department antitrust division—that also involved Canadian auto parts giant Magna International Inc.

In Magnas case, the investigation centres on bids by its Cosma Int. unit. Cosma produces vehicle body and chassis systems and provides vehicle engineering services.

Court documents filed in a Detroit federal court say the Japanese companies and executives sold automotive electrical components to automakers in the U.S. and elsewher at inflated prices.

The Justice Department has been building its case on the bid-rigging and price-fixing since January 2000.

It would not comment on which automakers were affected by the conspiracy or how much the price-fixing scheme inflated vehicle prices as the investigation continues. But investigators say theres no doubt consumers were hurt financially.

The two-year sentences against the executives would be the longest prison term ever imposed on a foreign national voluntarily submitting to U.S. jurisdiction for a Sherman Act antitrust violation, the Justice Department said.