DTC P010500 – Engine Coolant Temperature (ECT) Sensor 1 Circuit.

🔧 DTC P010500 – ECT Sensor 1 Circuit (General Fault)

This code indicates a problem in the Engine Coolant Temperature Sensor (ECT) circuit.
The ECM is detecting an abnormal voltage — could be open circuit, short circuit, poor connection, or sensor fault.

📌 Symptoms

You may notice:

Hard starting (cold or hot)

High idle / rough idle

Engine fan always ON or not turning ON

Poor mileage

Temperature gauge not working correctly

Black smoke (rich mixture)

🔍 Possible Causes

1. Faulty ECT Sensor

2. Open circuit / broken wire in the ECT harness

3. Short to ground or short to power

4. Corroded or loose connector pins

5. Low coolant level or air pocket near sensor

6. Faulty ECM (rare)

🛠️ Step-by-Step Diagnostic Procedure

1. Check Coolant Level

Ensure coolant is full.

Airlock near sensor can give wrong readings.

2. Visual Inspection

Locate ECT Sensor 1 (usually near thermostat housing or cylinder head).

Inspect:

Broken wires

Damaged insulation

Corroded connector pins

Loose or oil-soaked plug

👉 Repair wiring before going further.

3. Scan Tool Live Data

Check ECT temperature reading:

Normal Observations

Cold engine: usually equals ambient temperature.
(Eg: if outside is 30°C, ECT should show 28–35°C)

Warm engine: around 80–100°C.

If Reading Shows:

–40°C → Open circuit

140°C or more → Short to ground / short to power

Unstable jumping values → Intermittent wiring / sensor fault

4. Test ECT Sensor (Resistance Test)

Disconnect sensor → measure resistance with multimeter.

Approx values (may vary by manufacturer):

20°C → 2–3 kΩ

40°C → 1 kΩ

80°C → 300–400 Ω

If values do not match or don’t change with temperature → replace sensor.

5. Check Wiring Voltage

With ignition ON:

5V reference supply should be present on one pin.

Good ground on the other pin.

If no 5V → problem in wiring or ECU.

6. Fixes Based on Findings

Problem Found Solution

Sensor faulty Replace ECT sensor
Corroded pins Clean/replace connector
Open circuit Repair wiring
Short circuit Find short and correct
Air in coolant Bleed cooling system
No 5V ref Check harness/ECM driver

•After Repair

Clear DTC

Start engine

Monitor ECT temperature reading

Confirm fan operation and no return of code.

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