Sorry, your comment is incorrect again. The most recent version of CEN 15722 requires the two most recent locations before the incident location.
The modem does not have to passively track the mobile networks; it can do what it wants. The common OEM implementation these days is that the physical device that does eCall does several things, including eCall, over the same cellular radio. There's nothing stopping the OEM from connecting to a random website and eval()ing the result.
You seem confident in the security of this unhackable system so I will point out some of its other security weaknesses. Several eCall device implementations include Bluetooth modules (both "unused" as part of hardware and implementations that use Bluetooth.) Bluetooth is as secure as a wet cardboard box, so you could take BlueBorne or one of the six million other Bluetooth exploits that work on a non-discoverable device just sitting on the shelf, get in that way and boom, you can transmit whatever you want over the cellular radios. Vehicle infotainment systems are pretty insecure on average and are frequently hacked, so you could take over the infotainment system, get into the CAN bus that way and then send bad data to the eCall system, which is in the business of processing and responding to CAN data.
But those are just a few of the million ways; you could write up attacks all day long and you wouldn't scratch the surface. The facts are: this is a system with cellular radio(s), a CAN bus connection, sensors that constantly listen and interpret data; this is a large attack surface, built by OEMs that write notoriously insecure software. It is, by any reasonable judgment of those facts, a pretty hackable system. And yet, the European Commission goes around telling people that it "cannot" be hacked.
Anyway, this will be my third comment in a row here telling people that their comment is plain incorrect, so I'm going to have to leave the discussion here. I hope that my words provide some food for thought - for the next time that a system that could track you becomes legally mandatory.