To help identify faults or plan maintenance, manufacturers are able to gather performance data from connected cars such as the total distance travelled, or the length and number of trips made.
But drivers may be unaware of just how much other information such cars allow manufacturers to gather about them.
A study conducted by German motorists organization ADAC for European lobby group FIA Region 1 found that in addition to trip and distance data, one recent model reported maximum engine revolutions, the status of vehicle lights -- and far more besides.
The car, a BMW 320d, also recorded the length of time the driver used different driving modes, and recorded when the seatbelt tightened due to sudden braking. More sinisterly, it also transmitted the latest destinations entered into the car's navigation system, and personal information such as contacts synchronized from mobile phones.
ADAC only examined one car, and wants to extend the study to see how other brands behave, a spokeswoman said.
But FIA wants car manufacturers to come clean themselves, without waiting to be unmasked: It asked them to publish an easily understandable list for each model of all the data collected, processed, stored and transmitted externally.
With the risk that the data might be intercepted or the car hacked and the data taken, FIA wants carmakers to secure the data, and to make it possible for drivers to block the processing or transmission of non-essential data.
It will soon be impossible for car buyers to purchase non-connected vehicles in Europe, as from April 2018 all new vehicles must include support for eCall, a system that in case of accident automatically communicates its exact location to emergency services, with the time of incident and the direction of travel (most important on motorways). To do that, it will need to be continuously monitoring its position and have a mobile data connection to report back in case of incident.
Once automotive manufacturers have gone to the trouble of installing such hardware, it's unlikely they will pass up the opportunity to link in potentially revenue-generating services such as music streaming, traffic information or location-based recommendations.
Should they take that step, though, FIA wants them to give car owners the opportunity to switch providers for such services, as it believes that that way they will get the lowest prices and the most innovative products.
The motorists' organizations have launched a campaign to promote motorists privacy rights and their freedom to choose service providers: My Car, My Data.