Despite concern about Toyota acceleration problems, Corolla sales rose nine per cent in February in Canada. (Jeff Chiu/The Associated Press)

Toyota drivers have told U.S. safety officials that a fix for uncontrolled acceleration problems didn't work in at least 15 cases, The Associated Press reported Thursday.

Toyota undertook a massive recall to fix the acceleration problems, but the reports to the U.S. National Highway Traffic Safety Administration suggest that the cause of the sudden speedups may be electronic, not physical problems with the gas pedal or driver error.

NHTSA said Wednesday that it was contacting people who had complained of problems after their Toyotas were repaired.

The company, a leading international auto maker, has recalled more than eight million vehicles since October. The NHTSA said 52 people have been killed in the U.S. in crashes linked with acceleration problems in Toyotas.

The problems have prompted official investigations, including one promised by Canada's federal government, and a class-action lawsuit.

Shirley MacDonald, 76, of Port Coquitlam, B.C., is one of 156 people in the province who have joined the suit.

She was driving to church last summer in her 2004 Toyota Echo when the car suddenly accelerated and ran into a tree.

The car was totalled but MacDonald was not badly hurt. She drives a Nissan now.

But the bad publicity doesn't appear to have affected Toyota's Canadian sales.

The company said it sold 25.2 per cent more vehicles in February than it did in February 2009, including 2,906 of the popular Corollas, whose sales were up nine per cent.

With files from The Associated Press