A German government commission is seeking further explanation from General Motors Co.'s Opel division regarding diesel engines that can disable some pollution controls under certain circumstances.

Opel officials appeared Wednesday before the panel looking into diesel emissions controls following a report last week by environmental group DUH and the weekly Der Spiegel that the Zafira model reduces pollution controls at some speeds and temperatures.

Transport Minister Alexander Dobrindt said the company acknowledged that controls are reduced above 145 kph (90 mph) and below a certain air pressure, but said the panel had doubts as to whether that is designed to protect the engine. Opel is to submit technical details within two weeks.

The automaker denies doing anything illegal.