Engine Coolant Temperature Sensor 1 Circuit High

What it means

The engine computer has seen an engine coolant temperature (ECT) signal voltage above the highest acceptable level, so it reads the engine as very cold even when warm. It adds extra fuel and the mixture runs rich; the most common cause is an open circuit such as an unplugged connector, a broken wire or a failed sensor.

Related codes: P0115P0116P0117P0119P0113P0172

Symptoms5

• Check engine light on.
• Clearly higher fuel consumption or black smoke.
• Radiator fans running constantly as a precaution on many cars.
• Hard starting when the engine is hot.
• Temperature gauge staying low on some cars.

Possible causes5

• Unplugged sensor connector or corroded pins.
• Open circuit in the signal or ground wire.
• Internal open circuit in the coolant temperature sensor.
• Signal wire shorted to the reference voltage or another voltage source.
• Engine computer fault (rare).

How to diagnose5

1. Watch the reading on a scan tool; a value stuck at the lowest possible temperature with a warm engine means an open circuit.
2. Inspect the connector and make sure it is seated with good pins.
3. Bridge the signal and ground pins in the connector with a jumper wire; if the reading jumps to the highest value, the wiring is good and the sensor is faulty.
4. Check continuity of the signal and ground wires to the computer.
5. Measure sensor resistance and compare with the manufacturer table.

How to fix4

1. Reconnect the connector or clean its pins.
2. Repair the broken wire.
3. Replace the coolant temperature sensor if it is open internally, then top up the coolant.
4. Clear the codes and confirm the reading rises as the engine warms and fuel use returns to normal.

The cost is low for a connector or wire repair, and a little higher for a new sensor when 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