What is the primary reason for engines failing to start?

The primary reason engines fail to start is low battery voltage. The battery provides the necessary electrical power to crank the engine and operate the ignition system. If the battery voltage is insufficient, it may not deliver enough current to start the engine, leading to a failure to crank or an engine that turns over weakly. This is particularly common in colder weather when battery performance can diminish, or if the battery is old or has been improperly maintained.

While issues with the ignition system, fuel supply, or air intake can also contribute to starting problems, they usually involve factors that become evident once the engine has been cranked or if the electrical demand is met. In contrast, low battery voltage directly impacts the ability to initiate that process at all, making it a fundamental reason for a no-start condition.