P0117 - Engine Coolant Temperature Circuit Low Input
P0117 means the coolant temperature signal is reading hotter than expected because the signal is low or the circuit is shorted low. It is not automatically just a bad coolant temperature sensor; a shorted sensor circuit, damaged wiring, connector contamination, failed sensor, poor reference or ground behavior, or real overheating and low coolant in some cases can set the same code.
Code first. Confirm symptoms and checks before pricing parts.
Explore Related Systems
Compare nearby repair families.
Common Next Steps
Turn the code into the next check.
Confirm external leaks, cap behavior, and pressure loss before parts.
Compare warm-up, scan temperature, and hose temperature behavior.
Check fan command, AC-load response, fuses, relays, and airflow.
Related Inspection
Code Overview
P0117 means the coolant temperature signal is reading hotter than expected because the signal is low or the circuit is shorted low. It is not automatically just a bad coolant temperature sensor; a shorted sensor circuit, damaged wiring, connector contamination, failed sensor, poor reference or ground behavior, or real overheating and low coolant in some cases can set the same code.
Common Causes
- Short to ground in the ECT signal circuit
- Failed coolant temperature sensor reading too hot
- Connector contamination or damaged terminals
- Wiring rubbed through near the engine or thermostat housing
Symptoms
- Hard warm restarts or lean cold-start behavior
- Cooling fans may run more than expected
- Check-engine light with temperature data stuck too hot
Diagnostic Steps
- Inspect the coolant temperature sensor connector for coolant intrusion or corrosion
- Check the harness for a short to ground or damaged insulation
- Compare ECT reading to actual engine temperature on a cold start
- Verify sensor resistance and reference voltage before replacing parts
Diagnostic Insight
P0117 should be treated as a coolant-temperature circuit-low fault until testing confirms whether the engine is actually hot or the signal is being pulled low.
- A hot-looking ECT reading on a cold engine often points to a shorted circuit, contaminated connector, or failed sensor.
- Real overheating and low coolant still need to be ruled out before treating the reading as false.
- Connector, wiring, reference, and ground checks usually come before replacing the sensor.
Repair Difficulty
Easy
General difficulty estimate for the most common repair path.
Likely Repairs & Cost Guides
Confirm the repair path before pricing parts.
Estimator-ready next step after the fault path is confirmed.
Related OBD Codes
Browse nearby codes when systems overlap.
Next Steps
Move from code to checks, then estimate.