WASHINGTON – Federal regulators are opening a second inquiry into whether Toyota delayed notifying the government of a dangerous defect, this one affecting the steering systems of nearly 1 million sport utility vehicles and pickup trucks.

The probe by the National Highway Traffic Safety Administration comes a little more than a month after the agency fined Toyota $16.4 million for waiting at least four months before notifying safety officials about a “sticky pedal” defect. That sanction was the largest financial penalty imposed by the U.S. government on an automaker.

The new investigation involves the steering-relay rod on the Toyota 4Runner, Toyota Truck and Toyota T100s affecting some models made from 1989 through 1998. The rod, which connects the steering wheel to the wheels, can break after wear and tear and cause drivers to lose control. The safety agency has linked the defect to complaints involving at least 15 crashes, three deaths and seven injuries.

Toyota issued a recall for the steering defect in September 2005. It had issued a similar recall in Japan nearly a year before that, and the company’s critics have said Toyota and NHTSA should have realized more quickly that the same problem existed in the United States.

Automakers are required to notify the NHTSA within five working days of learning that their vehicles have a safety defect.

Toyota explained at the time that the first recall was issued only in Japan because the company had no similar information on the defect in the United States. Moreover, the company said, it thought the problem was unlikely to appear in the United States because Japanese drivers do more close-quarters maneuvering, such as for narrow parking spaces, that would put more stress on the steering.

On Friday, said the NHTSA, the agency was alerted to 41 complaints filed by U.S. consumers before the 2004 recall in Japan, indicating that Toyota had information at the time indicating a recall was necessary.

Toyota said in a statement that it “will cooperate with the agency’s investigation.”

Some consumer advocates said the incident reflects poorly on Toyota as well as the agency.

“Toyota said they turned the cars harder in Japan because they have tighter parking spaces — that’s poppycock,” said Joan Claybrook, a consumer advocate and ex-NHTSA chief. “NHTSA was asleep at the wheel.”

NHTSA learned that Toyota had received complaints from U.S. consumers about the faulty steering rod before the 2004 recall from a California law firm representing the family of an Idaho 18-year-old killed when his 1991 Toyota pickup crashed.

“Toyota was clearly warned by at least 40 U.S. customers that their steering rods had snapped and they were losing control of their trucks and pickups,” said John Kristensen, a California attorney representing the family of Michael “Levi” Stewart.

“And then they told the U.S. government that there was no similar information in the U.S.? That was completely false.”

Stewart’s truck veered off the road and rolled over after the steering rod snapped, according to the lawsuit.