Engine Coolant Temperature Sensor 1 Circuit Low
What it means
The engine computer has seen an engine coolant temperature (ECT) signal voltage below the lowest acceptable level, which means a very hot reading. The cause is usually the signal wire shorted to ground or an internal sensor short, but first make sure the engine is not really overheating.
Related lights
Dashboard lights that may come on with this code.
Symptoms5
- Check engine light on.
- Radiator fans running constantly at full speed.
- High temperature gauge on some cars even though the engine is not hot.
- Hard cold starting because the computer thinks the engine is hot.
- The computer may reduce engine power for protection.
Possible causes5
- Signal wire shorted to ground through damaged insulation.
- Internal short in the coolant temperature sensor.
- Coolant or water in the connector.
- Genuine engine overheating in some cases.
- Engine computer fault (rare).
How to diagnose5
- Before anything else, check the coolant level and the real engine temperature with an external thermometer.
- Watch the reading on a scan tool; a very high value with a cold engine means an electrical fault.
- Unplug the sensor with the key on; if the reading flips to the lowest value, the short is most likely inside the sensor.
- If the reading stays high with the sensor unplugged, look for a short to ground in the signal wire.
- Inspect the connector for coolant or corrosion.
How to fix5
- Fix any real overheating or low coolant first.
- Dry and clean the connector and fix the leak dripping on it.
- Repair the damaged insulation on the signal wire.
- Replace the coolant temperature sensor if the short is internal, then top up the coolant.
- Clear the codes and confirm the reading starts near outside temperature and rises steadily.
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 wire or connector repair and a little higher for a new sensor; it can differ greatly if the engine turns out to be really overheating.
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
Does this code mean the engine is really overheating?
Usually not; the most common cause is an electrical short. Still, check the coolant and real temperature before driving, because genuine overheating is dangerous.
Why is the car hard to start in the morning with this code?
Because the computer thinks the engine is hot, so it does not add the extra fuel a cold engine needs to start.
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