Engine Coolant Temperature Sensor 1 Circuit Intermittent

What it means

The engine computer has seen the engine coolant temperature (ECT) reading jump suddenly or drop out for short periods, a change real engine temperature cannot make so quickly. The cause is usually a weak connection in the connector or wiring, and it can make the fans switch on suddenly or the temperature gauge flicker.

Related codes: P0115P0116P0117P0118

Symptoms4

• Check engine light that comes on and goes off.
• Sudden temperature gauge swings on some cars.
• Radiator fans switching on and off for no clear reason.
• Intermittent stumbling or hesitation.

Possible causes5

• Loose or corroded connector pins from heat or coolant leaks.
• Internally cracked wire or a wire rubbing on metal.
• Weak shared ground point.
• Intermittent internal sensor failure.
• Air pocket in the cooling system that sometimes exposes the sensor to air.

How to diagnose5

1. Review the freeze frame data to learn when the fault occurred.
2. Watch the coolant temperature reading on a scan tool while gently moving the harness and connector, looking for jumps.
3. Inspect the connector pins for grip and corrosion.
4. Check the coolant level and make sure there is no air in the system.
5. Trace the harness for rubbing points near hot parts.

How to fix5

1. Clean the connector pins or replace the connector.
2. Repair the chafed harness and secure it away from heat.
3. Top up the coolant and bleed air from the system.
4. Replace the coolant temperature sensor if its reading still jumps with good wiring.
5. Clear the codes and drive until the engine reaches operating temperature to confirm a steady reading.

The fix is often a low-cost connector or wire repair; it rises a little for a new sensor or a long fault trace.

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