When troubleshooting a non-starting engine, what should be checked first?

When troubleshooting a non-starting engine, the first aspect to check is the battery charge. The battery is essential for providing the electrical power necessary to start the engine. If the battery is weak or dead, it won't be able to supply sufficient voltage to the starter motor, which is responsible for cranking the engine.

Checking the battery charge is crucial because it can often be the simplest and quickest fix. A charged battery can lead to a successful start, while a depleted one will obviously prevent the engine from starting. It could also be helpful to inspect connections and cables for corrosion or loose connections, which could also impact battery performance.

While the engine oil level, transmission fluid, and tire pressure are important factors for the overall health and performance of the vehicle, they are not directly related to the engine's ability to start. The engine oil level may affect the engine's operation once it's running, but it does not prevent it from starting initially. Similarly, while transmission fluid is critical for drivetrain performance, it does not impact whether the engine will crank. Tire pressure affects vehicle handling but has no effect on the engine's starting sequence. Thus, beginning the troubleshooting process with the battery charge is the most logical and effective approach.