P0117: OBD-II code P0117 means the engine coolant temperature (ECT) sensor is reading impossibly cold — typically a short-to-ground or a failed sensor.

Symptoms

• Check engine light is on and the engine may run rich because the PCM thinks it is stone cold.
• Cooling fans may run continuously as the PCM defaults to a safe high-temperature fallback strategy.
• The dashboard temperature gauge may sit at the cold end even after the engine is fully warmed up.

Common causes

• A shorted-to-ground signal wire between the ECT sensor and the PCM.
• A failed ECT sensor with an internally shorted thermistor reading effectively zero ohms.
• Corroded pins in the ECT connector creating a low-resistance leakage path to ground.

What to do?

Disconnect the ECT sensor — the reading should jump to −40 °F (open circuit). If it stays low, the signal wire is shorted to ground somewhere along its path. Measure sensor resistance cold vs hot with a DMM and compare to spec. Replace sensor, repair wiring, or clean the connector as needed.