P0118: Engine Coolant Temperature Circuit High Input

What does P0118 mean?

P0118 is a diagnostic trouble code indicating "Engine Coolant Temperature Circuit High Input". The ECU is reading a voltage that is above the expected range. This can be caused by a short to power in the wiring, a failed sensor, or a connector issue in the cooling system.

Symptoms you may notice

• Check engine light (MIL) illuminated on dashboard
• Engine overheating
• Temperature gauge reading high
• Heater not working properly
• Intermittent warning lights

Common causes

• Damaged or corroded wiring harness
• Loose or disconnected electrical connector
• Failed cooling system sensor or actuator
• Blown fuse in the related circuit
• Poor ground connection

What should you do?

This code sits in an engine peripheral, typically emissions or forced induction. It will not take braking or steering away, but it can put the car into limp mode, cost you fuel and fail a roadworthy. Book it in rather than clearing it and hoping.