ASE Advanced Engine Performance Specialist Certification (L1) Practice Test 2025 - Free ASE L1 Exam Practice Questions and Study Guide

In the scenario described, the vehicle is showing high RPM while the throttle body is at a low voltage of 0.5V, which suggests that the engine is not receiving the expected amount of air for the given conditions. This situation can indicate a potential vacuum leak.

When there’s a vacuum leak, excess air enters the intake manifold, causing the engine to rev higher than it should at a low throttle position. This discrepancy between the high RPM reading and the low throttle voltage signals that the engine is drawing in air without corresponding input from the throttle. A properly functioning throttle body would generally show a higher voltage during high RPM conditions, as more air would be entering the system.

This situation contrasts with the other options, which would produce different symptoms. For instance, low fuel pressure would typically result in poor engine performance or stalling rather than high RPM, while rich and lean conditions would manifest differently in terms of exhaust emissions and engine response at various throttle positions. Thus, the presence of a vacuum leak is the most likely explanation for the given sensor reading and engine behavior.