Can I assume a modifier refers to the object of a sentence

Hi Gordon,

This indeed is an easy question.

Let's begin from the beginning.

When the car was crashing into the light pole, its bumper protected the driver from being hurt.

"its" is a Pronoun. Pronoun errors are one of the errors that are tested on GMAT in two respects:
a. the sense that they must refer to some noun entity in the sentence
b. they must agree in number with the noun entity they refer to

Another important thing to remember about Pronouns is that they must refer to a logical entity, something the usage must make with. For example, in your sentence, there is no ambiguity about the reference of "its" because only "the car" has a bumper. Another singular entity in the sentence that agrees in number with the singular pronoun "its" is "the light pole". But a light pole does not have bumper. Hence, there is NO ambiguity that "its" does refer to "that car".

Also, generally on GMAT, a pronoun in the Subject place grammatically refers to a noun in the Subject place. So in that respect as well, your sentence has no ambiguity at all.

In our course, we cover the topic of Pronoun reference in great details. One of our experts have also written a one-of-its-kind detailed article on the myths related the Pronoun usage. Following is the link:
pronouns-debunking-popular-myths-intro-160811.html

Hope this helps.
Thanks.
SJ