P0118: OBD-II code P0118 means the engine coolant temperature (ECT) sensor is reading impossibly hot — typically an open circuit or a failed sensor.

Symptoms

• Check engine light is on; cold-start enrichment is disabled, so cold starts are hard and rough.
• Cooling fans may run continuously or the PCM may enter overheating-protection strategy even when the engine is cool.
• The temperature gauge may sit pegged at hot or read erratically depending on where the fault lies.

Common causes

• A failed ECT sensor with an internally open thermistor — the most common cause of this code.
• An unplugged ECT connector or a broken signal wire between the sensor and PCM.
• Corroded connector pins adding resistance that biases the signal reading falsely high.

What to do?

Read live ECT — a persistent 250 °F+ reading with a cold engine confirms the fault. Disconnect the sensor; if the reading changes, the sensor is bad. If it stays high, the wiring is open. Replace the sensor or repair the wiring.