DTC P010700 – Engine Coolant Temperature (ECT) Sensor 1 Circuit Low.

✅ P010700 – ECT Sensor 1 Circuit Low

This code means the ECM is seeing a very low voltage from the engine coolant temperature sensor.
Low voltage = ECM thinks the coolant temperature is very cold (–40°C / –40°F).

🔧 Common Causes

Cause Description

Faulty ECT sensor Internal short causing low signal.
Wiring short to ground Signal wire touching ground or damaged insulation.
Corroded/loose connector pins Poor connection → low voltage.
Low coolant level Sensor not immersed in coolant.
Faulty thermostat (stuck open) Engine stays cool → ECM thinks temperature is low.
ECM fault (rare) Only after all other checks.

🧰 Step-by-step Diagnosis

1. Scan Live Data

Check ECT temperature on scanner:

If reads –40°C or extremely low → open circuit / sensor unplugged.

If reads 0–20°C even after warming up → sensor is faulty / shorted.

Compare with:

Intake air temperature (IAT)

Ambient temperature
Both should be almost equal when engine is cold.

2. Inspect Coolant Level

Low coolant = sensor not touching coolant → wrong readings.
Top up if low & check for leaks.

3. Check ECT Sensor Connector

Look for:

Corrosion (green color)

Loose pins

Broken lock tab

Oil/coolant contamination

Clean and refit tightly.

4. Wiring Check

Using a multimeter:

Signal Wire → ECM

Should have 5V reference with sensor unplugged.

If less than 4.5V → short to ground.

Ground Wire

Ensure proper grounding (<0.1Ω resistance).

If wiring is damaged → repair or replace.

5. Sensor Resistance Test (Ohm Test)

Remove sensor → measure resistance:

Coolant Temp Typical Resistance

20°C 2,000–3,000 Ω
80–90°C 200–300 Ω

If readings are far off → replace sensor.

6. Thermostat Check

If thermostat is stuck open, engine does not reach operating temperature → low ECT reading.

Symptoms:

Poor fuel economy

Weak heater

Engine takes long time to warm

Replace thermostat if needed.

🛠️ Most Common Fixes

✅ Replace ECT sensor
✅ Repair corroded connector
✅ Repair short-to-ground wiring
✅ Top up coolant / fix leaks
✅ Replace thermostat.

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