What Does P0118 Mean?
The ECM has detected that the engine coolant temperature (ECT) sensor signal voltage exceeds the expected maximum threshold, indicating a reading below approximately -40°F (-40°C). This typically points to an open circuit condition in the ECT sensor wiring or a failed sensor element, causing the ECM to use a default coolant temperature value that degrades fuel economy and cold-start performance.
Common Causes
40%
Failed ECT sensor with open-circuit internal thermistor element
25%
Open or broken wire in ECT sensor signal circuit between sensor and ECM
20%
Corroded or damaged ECT sensor connector causing high resistance or open circuit
15%
Faulty ECM with internal pull-up resistor or A/D converter failure on ECT input
Diagnostic Steps
1
Inspect the ECT sensor connector for corrosion, bent pins, moisture intrusion, or broken locking tabs. Disconnect and reconnect to verify proper seating.
2
With the sensor connected and key on engine off, backprobe the ECT signal wire at the ECM connector and measure voltage. A reading near 5V indicates an open circuit in the sensor or wiring.
3
Disconnect the ECT sensor and measure resistance across the sensor terminals. At 68°F (20°C), resistance should be approximately 2,000-3,000 ohms. An OL (open) reading confirms a failed sensor.
4
If sensor resistance is within spec, check continuity of the signal and ground wires from the ECT sensor connector to the ECM connector pins. Repair any open circuits found.
5
Jumper the ECT sensor connector terminals together and verify the scan tool reads an extremely high temperature (near 280°F). This confirms wiring integrity back to the ECM.
Estimated Repair Cost
$50 - $250
Parts + labor, varies by vehicle and location
The ECM has detected that the engine coolant temperature (ECT) sensor signal voltage exceeds the expected maximum threshold, indicating a reading below approximately -40°F (-40°C). This typically points to an open circuit condition in the ECT sensor wiring or a failed sensor element, causing the ECM...
The most common cause of P0118 (Engine Coolant Temperature Sensor High Out of Range Fault) is: Failed ECT sensor with open-circuit internal thermistor element
Typical repair costs for P0118 range from $50 to $250, depending on the vehicle, location, and whether you do it yourself or go to a shop.
While not immediately dangerous, the ECM will default to a fixed coolant temperature value, causing rich fuel mixtures, elevated emissions, and potential catalyst damage over time. Extended driving may mask actual overheating conditions.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0118 to identify the root cause.
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Quick Info
Category
Powertrain
System
Engine Cooling & Fuel Management System
Difficulty
Type
Generic (SAE)
Recommended Tools
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