DTC P010800 – Engine Coolant Temperature Sensor 1 (ECT) Circuit High.

✅ P010800 – ECT Sensor 1 Circuit High Input

This code means the ECU is receiving a higher-than-expected voltage from the coolant temperature sensor (ECT).
High signal voltage = ECU thinks engine coolant temperature is extremely low (cold) → open circuit, damaged sensor, or wiring fault.

🔧 Common Symptoms

Hard cold starting

High idle RPM

Rich fuel mixture

Black smoke

Poor mileage

Radiator fan may run continuously

Temperature gauge not working / stuck low

🎯 posible causes

Sensor / Wiring Related

1. ECT sensor unplugged / loose connector

2. ECT sensor internal open circuit

3. Signal wire open (broken wire)

4. Signal wire shorted to battery voltage (5V)

5. Ground wire open

6. Corroded pins or coolant intrusion

ECU Related

7. Faulty ECU (rare)

🔍 Step-By-Step Diagnosis (Workshop Method)

1. Visual Inspection (Always first)

Check ECT sensor connector – push tight

Look for corrosion, rust, oil, coolant contamination

Inspect wiring for cuts, rodent bites, loose pins

2. Check Coolant Temperature on Scanner

Key ON, cold engine

Live data should read near ambient temperature (20–35°C)

If scanner shows –30°C, –40°C or very low values, → signal voltage is high → open circuit fault.

3. Check Reference Voltage

Unplug ECT sensor

Measure between 5V reference wire and ground

Should be approx. 5V

If 5V is missing → ECU or wiring issue.

4. Check Ground

Check ground wire continuity

Resistance should be < 1 ohm

Open ground = high circuit signal.

5. Sensor Resistance Check

ECT sensor is NTC type ↑ temp = ↓ resistance.

Typical values:

Cold engine (20–25°C): 2k–3k ohms

Hot engine (80–90°C): 200–300 ohms

If sensor shows:

Infinite resistance (open circuit) → Sensor faulty → replace.

6. Wiggle Test

With live data running, wiggle harness

If temperature jumps → wiring fault.

🛠️ Most Common Fixes

🌟 Clean & tighten ECT sensor connector
🌟 Repair broken/open wires
🌟 Replace corroded connector
🌟 Replace faulty ECT sensor
🌟 Clear DTC and recheck live data

ECU replacement is rarely needed.

Welcome To Madurai Car Service 💐🙏🏻.