PGM-FI Series Part 8: What is EOT Sensor? Function, symptoms of failure, how to test. Based on Honda Satu Hati Education series.
What is EOT Sensor?
EOT = Engine Oil Temperature Sensor (also called ECT on liquid-cooled). On Honda manual bikes CB150R, Supra GTR, Sonic, it's screwed into cylinder head / crankcase, measuring oil or coolant temperature. It's NTC thermistor like IAT - resistance drops as engine gets hotter.
Function
- Cold Enrichment: When EOT reads cold (e.g., 20°C), ECU adds extra fuel for easy cold start and fast idle
- Warm-up Compensation: Gradually reduces fuel as engine warms to 80-90°C
- Fan Control (if equipped): Triggers radiator fan at ~100°C
- Overheat Protection: If too hot, ECU may limit RPM
Symptoms of Bad EOT Sensor
1. MIL Code 7-1 / 7-2
Honda MIL 7 blinks = EOT circuit problem. 7-1 = open circuit, 7-2 = short circuit
2. Very Hard Cold Start
EOT reads hot when actually cold = ECU gives too little fuel. Need many cranks in morning
3. Rich Running, Black Spark Plug, High Fuel Consumption
EOT reads cold all time = ECU always enriches. Spark plug sooty black.
4. Idle Too High When Hot or Too Low When Cold
5. Fan Not Working / Engine Overheating
How to Test EOT Sensor
Resistance Test (Unplugged, Key OFF)
- At 20°C (cold engine, morning): ~2.5-3.0 kΩ
- At 80°C (warm engine, after 5 min ride): ~0.3-0.5 kΩ
- At 100°C: ~0.15-0.25 kΩ
- Open (OL) or 0Ω = bad sensor
Voltage Test (Plugged, Key ON)
Signal wire ~2.5-3V at cold, drops to ~0.5V at hot. If stuck, bad.
Quick Test
Unplug EOT when engine cold - if engine starts easier, EOT is reading wrong (too hot). Or dip sensor in hot water - resistance should drop quickly.
Fix
Check connector for oil contamination, check wiring for melt near exhaust. Replace sensor with new O-ring. Clear MIL code after. Use OEM for accurate temp.
Labels: Honda Service Guides, Electrical System, Engine & Transmission, Troubleshooting