DIGITAL DISPLAY CIRCUIT TESTER: Equipped with LED display showing real-time voltage readings from 5V-30V, making electrical diagnostics clear even in low light conditions with the built-in rear light illumination for nighttime repairs. AUTOMOTIVE ELECTRICAL DIAGNOSTICS: Quickly identifies positive/negative poles through color-coded LED indicators (red for positive, green for battery negative), helping mechanics and DIY enthusiasts accurately detect circuit problems without guesswork. MULTI-FUNCTION TESTING CAPABILITY: Checks blown fuses, tests battery performance, detects short circuits, distinguishes between real/virtual electricity, examines ABS circuits, and verifies vehicle speed sensors - all with a compact tool for comprehensive vehicle troubleshooting. FREQUENCY MEASUREMENT MODE: When connected to AC signals (5-30V), displays estimated frequency ranges for injector signals, spark, and crankshaft sensor signals, providing advanced diagnostic information for professional automotive technicians. Use scenarios: - In daily maintenance, use the tester to verify polarity and fuse integrity, assess battery health, and perform quick checks in the engine bay with the rear light for visibility. - During wheel or ABS service, diagnose ABS circuits and speed sensor conditions with the color coded polarity indicators and fuse/battery tests, reducing guesswork. - For advanced diagnostics, connect to AC signals to read injector frequency, spark, and crankshaft sensor ranges, aiding professional troubleshooting and timing checks.