P0117 — Engine Coolant Temperature Sensor 1 Circuit Low

The controller detects excessively low voltage in coolant temperature sensor 1’s circuit. A conventional NTC input may interpret this as very high temperature. The electrical code alone does not establish actual engine overheating.

Affected system: Powertrain

Symptoms

• Difficult starting or unusual idle, depending on the calculated temperature.
• Higher consumption, engine warning light or a fallback fan strategy, depending on the vehicle.

Possible causes

• Corroded connector, open/shorted wiring or a failed sensor.
• Incorrect reference or ground; for plausibility faults, check actual coolant level and warm-up.

What to check

• With the engine cold, check coolant level and leaks; do not open the cap while the system is hot.
• After a complete cold soak, compare ECT with intake air and ambient temperature, allowing for location and residual heat.
• Inspect sensor 1’s connector and harness; test signal, supply and ground with the exact engine wiring diagram.
• Check for signal shorts to ground and compare voltage with actual temperature; test resistance against the installed sensor’s characteristic.
• After repair, clear codes and recheck ECT temperature under the original recorded conditions, following the manufacturer’s procedure.

Also written as: P0117-00, P011700, PO117 (some scan tools add the fault-type byte, e.g. -00).