[D_Alex]

Er, no, this is probably wrong. The voltage drop is due to resistive losses in the long (and skinny) cable, and the resistive losses depend on current flowing. So, unless there are some weird effects due to the car's electronics, you cannot stop the charging, only slow it down.

[marshray]

So the charger sees the 120 V, decides to begin charging, current flows, and the voltage drops. If the voltage drops out of range, the charger aborts because it's out of design spec and/or there's a significant amount of power being dissipated, probably by resistive heating (i.e., risk of fire).

This is probably necessary to achieve UL rating.