What Does P0117 Mean?
The ECM has detected that the Engine Coolant Temperature (ECT) sensor 1 is producing a voltage signal below the expected minimum. Since the ECT sensor is an NTC thermistor, low voltage means the ECM is seeing an implausibly high temperature, often over 280°F (138°C). This is almost always caused by a shorted sensor or wiring issue rather than actual extreme coolant temperatures. The ECM will substitute a default value, which may cause the cooling fan to run continuously and affect fuel metering.
Common Causes
35%
Internally shorted ECT sensor (thermistor resistance near zero)
25%
ECT signal wire shorted to ground in the harness
20%
Coolant or water intrusion in the ECT sensor connector causing short between pins
15%
Pinched or chafed ECT harness contacting engine block or bracket
5%
ECM internal fault pulling the ECT input low
Diagnostic Steps
1
Check live data — if the ECT reads an extremely high temperature (280°F+) when the engine is cold or at normal operating temperature, confirm the low-input fault.
2
Disconnect the ECT sensor connector. If the live data reading jumps to -40°F (maximum voltage), the harness wiring is good and the sensor is shorted internally.
3
Measure ECT sensor resistance across its terminals. At room temperature (68°F/20°C), expect 2.0-3.5 kOhms. A reading of zero or near-zero ohms confirms a shorted sensor.
4
If voltage remains low with the sensor disconnected, check the signal wire for a short to ground. Disconnect the ECM connector and measure resistance from the signal wire to chassis ground.
5
Inspect the ECT sensor connector and mounting area for coolant leaks that could cause corrosion or bridging between connector pins.
Estimated Repair Cost
$20 - $150
Parts + labor, varies by vehicle and location
The ECM has detected that the Engine Coolant Temperature (ECT) sensor 1 is producing a voltage signal below the expected minimum. Since the ECT sensor is an NTC thermistor, low voltage means the ECM is seeing an implausibly high temperature, often over 280°F (138°C). This is almost always caused by ...
The most common cause of P0117 (Engine Coolant Temperature Sensor Low Out of Range Fault) is: Internally shorted ECT sensor (thermistor resistance near zero)
Typical repair costs for P0117 range from $20 to $150, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Driveable but the cooling fan may run continuously (wasting energy and causing slow warm-up) and the ECM may lean out the fuel mixture thinking the engine is very hot. Monitor actual engine temperature with an infrared thermometer. If the real coolant temperature is normal, the risk is low.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0117 to identify the root cause.
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Quick Info
Category
Powertrain
System
Engine Cooling / Fuel Management
Difficulty
Type
Generic (SAE)
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