The two cars were found to have problems with the deployment of airbags.
In the frontal impact test of the Mazda, the firing of the airbags was delayed, compromising protection of the front seat occupants.
“Although these disturbances are not part of our tests, they could occur in real life accidents,” said Euro NCAP today.
Both manufacturers fixed the problems.
Mazda improved the airbag control software in production cars and will contact all Mazda 2 owners, to ensure their cars are upgraded.
Volvo agreed to modify production cars and to contact all V70 owners.
But despite the modifications the curtain airbag in the V70 fired late during a second round of testing. Volvo is investigating the cause and drivers are being urged to contact their dealer.
The Mazda 2 airbags deployed correctly.
Michiel van Ratingen, secretary general of Euro NCAP, said: “This is exactly why Euro NCAP exists: to independently evaluate the protection that these cars offer consumers and to spot just this kind of error. If there is a safety problem, we will not re-test the vehicle unless the problem is fixed on all cars.”
However, both cars received five out of five stars for adult occupant protection, alongside the Mercedes Benz C Class and Renault Laguna also assessed in the latest round of tests.
Mr van Ratingen explained what happened during testing of the Mazda2 and Volvo V70, and why both cars still received five stars despite problems with their airbag deployment.
"The cases of the Mazda and Volvo were both related to airbag deployment.
"However both were quite different in nature."
In relation to the Mazad2 test, he said: "During the frontal test, a high spike on the acceleration signal measured at the airbag sensor milliseconds before the crash caused the driver airbag to deploy late.
"The most likely cause of this was identified as a hard object (possibly the chain puling the vehicle) striking the sub frame.
"Although this is considered a test artefact, EuroNCAP believes that such event could happen on the road and that the airbag deployment should not be affected the way it did in the test.
"Mazda improved the airbag triggering algorithm accordingly."
Because Mazda rectified the problem and performed well in all other areas of adult occupant protection, it received five stars.
In relation to the Volvo V70, he said: "The side airbag of the Volvo incorrectly deployed during both pole tests. Whilst it gave sufficient protection based on the dummy head measurements, the EuroNCAP protocol penalises such incorrect deployment as it is clearly not as intended.
"Volvo is investigating what has caused this to happen.
"The V70 got the five-star rating based on a total adult score of 34 out of 37 points based on front, side and pole test results."
The Renault Laguna would have been Euro NCAP’s highest ever scorer in adult occupant protection if it had not lost a point for the opening of a rear door in the side impact test.
None of the cars achieved higher than three stars for pedestrian protection.
Today, Euro NCAP releases the results for six cars: the Daihatsu Materia, Mazda 2, Honda Civic, Mercedes Benz C Class, Renault Laguna and the Volvo V70.