DETROIT — General Motors recalled 3.4 million large cars last month after finding a 9-year-old email from an employee in its files warning of trouble, according to documents released by the government Thursday.

The 2005 email, unearthed in April during a companywide review of ignition-switch problems, is more evidence that GM knew about safety problems for years but failed to recall troubled cars until recently.

So far this year, GM has recalled 17.1 million vehicles to fix ignition-switch problems, raising questions about the safety of switches across the auto industry. The National Highway Traffic Safety Administration, the governments road safety agency, has asked for ignition data from all automakers and is looking into potential safety problems.

GMs troubles began early this year when it began recalling older small cars such as the Chevrolet Cobalt and Saturn Ion to fix faulty ignition switches. The company admitted knowing about the problem for at least a decade, yet it failed to start recalling the cars until February. GM says the switches have caused more than 13 deaths, although lawmakers say the death toll is closer to 100.

The small-car switches can slip out of the run position, causing engines to shut down, knocking out power steering and brakes. That can cause drivers to lose control, and if they crash, the air bags wont inflate. GMs reluctance to recall the cars for years has brought multiple federal investigations, a $35 million fine from NHTSA and numerous lawsuits from crash victims.

A company-funded investigation blamed the problem on a dysfunctional corporate culture and misconduct by some employees. Fifteen workers were dismissed.

After the problem surfaced, GM began looking for other safety problems across its model lineup that may not have been fixed. Thats resulted in 54 recalls involving a record 29 million vehicles so far this year.

The 2005 email warned that a 2006 Chevrolet Impala being tested before production had stalled because the ignition slipped from run to accessory after going over a bump. GM began testing switches in the Impala and other full-size cars in May, and found that they didnt meet company specifications. That led to a June 16 recall of 3.4 million cars, according to the document released by NHTSA.

In a chronology of the Impala recall, GM said the employee who wrote the email was driving an Impala that was in a fleet of vehicles being tested before production. The employee wasnt identified in the document, but a GM spokesman confirmed it was Laura Andres. Her email was disclosed during congressional hearings last month. GM would not comment further.

According to the chronology, GM engineers tested the car Andres was driving in August of 2005 but could not make it stall. They returned it to her and apparently made no changes. Her warning also was brushed off by GM ignition-switch engineer Ray DeGiorgio, who replied that he had recently driven an 06 Impala and did not experience this condition.

In April of this year, GM investigators found Andres email while doing the companywide safety review. She reported hitting a bump at 45 mph and the car stalled. A car behind her had to swerve to avoid a crash. She took it to a shop, and a technician identified the most likely culprit as a faulty ignition switch.

In the email to 11 GM colleagues, she warned of a serious safety problem and a big recall. I dont like to imagine a customer driving with their kids in the back seat, on I-75 and hitting a pothole, in rush hour traffic, she wrote.

Testing by GM done in May and June found that the switches could be pulled out of the run position if key chains were loaded with heavier items and the car went over a bump. The standard Impala keys have a wide slot to hold key rings, and that allows them to swing, creating force on the switches.

GM is recalling the cars to put an insert into the key ring slots that converts it to a small hole. That cuts the force generated by swinging key rings and stops the cars from stalling, GM said.

The recall affects Impalas, Cadillac Devilles and five other models. GM says owners should remove everything from their key rings until repairs are made.