Red Seal Automotive Service Technician Practice Exam

The activation of the "check engine" light is often associated with various issues detected in the vehicle's engine management system. A faulty oxygen sensor is a common cause for this warning light because this sensor plays a crucial role in measuring the amount of oxygen in the exhaust gases. It provides vital data to the Engine Control Unit (ECU), which uses this information to optimize fuel mixture and emissions control. When the oxygen sensor fails or operates outside its normal range, it can lead to issues such as poor fuel economy, increased emissions, and engine performance problems. These malfunctions trigger the onboard diagnostics system to alert the driver via the check engine light, indicating that immediate attention is needed to diagnose and rectify the issue.

In contrast, faulty brake pads and broken tail lights would not cause the check engine light to activate as they are managed by separate systems within the vehicle. Low oil levels, while serious and potentially leading to engine damage, do not specifically activate the check engine light; instead, that situation might trigger different alerts regarding oil levels or pressure.