KOEO

📖 YOUCANIC Automotive Glossary

KOEO (Key On Engine Off) is a diagnostic state where the ignition is ON/RUN but the engine is not running, so all electronic modules are powered and communicating. Sensors provide baseline readings: MAP sensor reads atmospheric pressure (~4.5V at sea level), TPS reads closed position (~0.5V), coolant and intake sensors read ambient temperature, ECU reports 0 RPM. KOEO establishes whether sensors provide correct baselines before the engine adds dynamic influence.

Many diagnostic procedures begin at KOEO. If a MAP sensor reads 3.5V instead of expected 4.5V before the engine starts, the sensor is faulty regardless of running readings. O2 sensor voltage at KOEO should read approximately 0.45V — stuck at 0V or 5V indicates wiring problems. KOEO is also when you verify all modules respond to your scanner — if a module does not communicate at KOEO, it will not at KOER either, pointing to power, ground, or network wiring issues.