Open Circuit

📖 YOUCANIC Automotive Glossary

An open circuit is a complete break in an electrical path that prevents current from flowing. In automotive electrical systems, opens can occur in wiring (broken wire inside insulation that looks intact from outside), at connectors (pushed-out or corroded pins that lose contact), in components (burned fuse, blown fusible link, open coil winding, burned-out filament), and at ground connections (corroded ground bolt, broken ground strap). An open circuit causes complete loss of function for the affected circuit — unlike a short which may blow fuses, an open simply prevents the circuit from working.

Open circuits generate DTCs referencing circuit high/low input: a sensor circuit that reads 0V when it should read 2.5V may have an open in the signal wire (ECU sees 0V because the pull-down to ground dominates), or reads 5V because the pull-up reference dominates. DIYers diagnose opens with a multimeter continuity test — disconnect both ends of the wire and test for continuity end to end. Intermittent opens (loose connections that make and break with vibration or temperature) are diagnosed by wiggling connectors and wiring while monitoring live data or continuity.