P0118 Code: Engine Coolant Temperature Sensor High Input
Quick Answer
The engine coolant temperature sensor is sending a higher voltage than expected — usually indicating an open circuit or a sensor that has failed to a 'cold' reading.
At a Glance
What this code means
P0118 is the opposite of P0117. The ECT sensor circuit voltage is above the maximum threshold, which usually means an open circuit (broken wire or failed sensor) causing the ECU to see a maximum resistance value. The ECU interprets this as an extremely cold engine and may apply cold-start enrichment indefinitely.
Common causes
- Faulty ECT sensor (open circuit/internal failure)
- Open or broken wire in the ECT sensor circuit
- Corroded or disconnected sensor connector
- Poor sensor ground
Symptoms you might notice
- Check engine light on
- Engine runs rich on warm starts (ECU thinks engine is always cold)
- Poor fuel economy
- Temperature gauge may not move from cold position
- Possible black smoke from exhaust
Can you still drive?
Yes. P0118 is usually a sensor or wiring issue, not a mechanical problem. Drive with caution and watch the temperature gauge for any real overheating signs.
How serious is this code?
Low to moderate. The engine will continue to run but may use excess fuel due to constant cold-start enrichment. Address it soon.
Before you replace parts
Parts replacement is often not the first step. Before buying anything, it's worth checking these basics:
- Disconnect and inspect the ECT connector — corroded pins are a very common cause and can be cleaned rather than replaced
- Check if the temperature gauge reads correctly — if the gauge works normally but the code appears, the sensor circuit is the issue not the actual temperature
How to troubleshoot it
- Inspect the ECT sensor wiring connector — disconnect and reconnect to rule out a loose connection
- Check the wiring harness from the sensor to the ECU for breaks or chafing
- Test the ECT sensor resistance with a multimeter — an open circuit sensor will read infinite resistance
- Replace the ECT sensor if the resistance is out of specification
Tools that may help
These are the types of tools commonly used when diagnosing this code. Having the right tool can save time and help confirm a diagnosis before spending money on parts.
- Multimeter
- OBD-II scanner with live coolant temp data
Estimated repair cost range
ECT sensor: $15–$80 for the part. Labor: $50–$150 depending on accessibility.
Costs vary significantly by vehicle, location, and whether you use OEM or aftermarket parts. These are general ranges for reference only.
When to call a mechanic
If you've completed the basic troubleshooting steps and the code keeps returning, or if you don't have access to the proper diagnostic tools, it's worth consulting a professional. A qualified technician can perform a full diagnosis and confirm the root cause before any parts are purchased. When in doubt, get a professional opinion — it can save you from an expensive misdiagnosis.
Real-world note
P0118 is usually a straightforward sensor or connector fix. The ECT sensor is a simple, inexpensive part on most vehicles. Check the connector first — a corroded terminal is a common cause.
Informational purposes only. This guide is for educational reference and is not a substitute for diagnosis by a qualified technician. Repair costs, causes, and symptoms may vary by vehicle make, model, year, and condition. Always consult a licensed mechanic before performing major repairs.