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Germany's transport ministry is to test a Porsche SUV model following reports it could be in breach of diesel emissions limits.

Der Spiegel magazine said it had tested the Cayenne V6 TDI and found its emissions were higher than allowed.

Porsche has said the Spiegel test was "implausible" and its vehicles meet emissions requirements.

Its sister company Volkswagen is to pay fines and compensation after admitting cheating on emissions tests in 2015.

Volkswagen fitted some of its diesel vehicles with "defeat device" software designed to detect testing and change performance to improve results.

Der Spiegel it had been told by a source that the Porsche Cayenne had a "warm up mode" whose true purpose was to comply with emissions requirements. It said tests showed that once the car was confronted with small bends or a slope it switched to a different mode and emissions were higher.

In a statement, Porsche said it had obtained extracts of Der Spiegel's test, carried out with technical inspection company TÃœV Nord, but found them unconvincing. It also noted that emissions depend on conditions such as engine load, speed and temperature, Reuters reported.

Porsche also said it had carried out tests on a comparable Cayenne V6 TDI following the Der Spiegel report and found the vehicle to comply with nitric oxide emission limits.

The company had offered to carry out joint tests with Der Spiegel but the magazine had refused, it said.