Here are the missing subjects.
1) When [you are] calling for roadside service, [you should] please have the following information readily available.
2) When [he is] discussing our sales performance, he pulls no punches.
3) When [?it is] gathering speed, this power along with power from a diesel engine is used to operate the motors.
4) When [they were] asked about kicking the habit, 60 percent [of them] said they could quit if they wanted to.Notice that the subjects agree in 1), 2) and 4), but not in 3).