KOER

📖 YOUCANIC Automotive Glossary

KOER (Key On Engine Running) is the diagnostic state with the engine running and all sensors reporting dynamic values. KOER is used for most live data monitoring, active tests, and diagnostics because sensors produce meaningful readings only when the engine runs. MAP sensor shows intake vacuum, O2 sensors produce switching voltages, MAF measures actual airflow, and fuel trims show real-time corrections. KOER testing lets you observe how the engine management system responds to load changes and accessory activation.

Comparing KOEO and KOER values reveals diagnostic information. A sensor correct at KOEO but erratic at KOER suggests heat, vibration, or electrical noise issues. Some functions are only available at KOER (injector balance test, power contribution test, live O2 monitoring), while others are restricted to KOEO for safety (throttle calibration, certain programming operations).