Engine Coolant Temperature Sensor 1 Circuit
What it means
The engine computer has detected an invalid signal from the engine coolant temperature (ECT) sensor. This sensor is one of the computer's key inputs for fueling, ignition timing and fan control, so the computer may run the fans constantly and use a backup value for protection.
Related lights
Dashboard lights that may come on with this code.
Symptoms5
- Check engine light on.
- Radiator fans running constantly, even with a cold engine.
- Hard starting or rough idle.
- Illogical temperature gauge on some cars.
- Higher fuel consumption or black smoke.
Possible causes5
- Unplugged connector or one corroded by leaking coolant.
- Open or shorted sensor wiring.
- Failed coolant temperature sensor.
- Weak ground shared with other sensors.
- Engine computer fault (rare).
How to diagnose5
- First check the coolant level and make sure the engine is not genuinely overheating.
- Watch the coolant temperature reading on a scan tool; a reading stuck at the lowest or highest possible value means an electrical fault.
- After a long rest, compare the reading with intake air and outside temperature.
- Inspect the connector and wiring for corrosion or coolant residue.
- Measure the sensor resistance and compare it with the manufacturer table.
How to fix4
- Clean and reconnect the connector, and fix any coolant leak dripping on it.
- Repair the open or shorted wire.
- Replace the coolant temperature sensor, then top up and bleed air from the cooling system.
- Clear the codes and confirm the reading rises steadily as the engine warms and the fans switch on at the right time.
Repair cost
In Saudi riyals; the highlighted part is the expected range for this fault.
In the Saudi market: SAR 80–500 (≈ USD 21–133)
Our prices come from the Saudi market, converted at a fixed rate (SAR 3.75 per USD). Prices in your country may differ a lot, so we show the cost level.
The cost is low for a connector or wire repair, and a little higher when the sensor is replaced and coolant added, especially if it is hard to reach.
Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026
Frequently asked questions
Why do the fans run all the time with this code?
Because the computer cannot trust the engine temperature reading, so it runs the fans as a precaution to protect the engine from overheating.
Can I drive with this code?
Short distances and carefully, while watching the temperature gauge and coolant, because the computer may not detect real overheating in time.
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