Engine Coolant Temperature Sensor 1 Circuit High Input
The P0118 code means the vehicle's onboard diagnostic system has detected: Engine Coolant Temperature Sensor 1 Circuit High Input. This is a moderate severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- easy
- Estimated cost
- $15-$50 for the ECT sensor part (DIY); a shop typically charges $100-$300 total (part plus labor), and $150-$500 if the fault is wiring or a corroded connector rather than the sensor
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Common Symptoms
- Check Engine Light on
- Engine runs rich on warm restarts
- Temperature gauge reads cold or not at all
- Heater may not work properly
- Hard warm starting
Probable Causes (Ranked by Likelihood)
- ECT sensor open circuit reading maximum resistance Very High
- Open signal wire between sensor and PCM High
- Disconnected sensor connector Moderate
- Corroded or broken sensor terminal Moderate
Step-by-Step Diagnostic Procedure
-
Check ECT signal voltage: above 4.7V at operating temperature indicates an open circuit.
-
Disconnect and reconnect the ECT connector. If the fault clears, the connector was loose.
-
Measure sensor resistance at operating temperature. Should be 200-300 ohms when hot. Infinite resistance indicates open sensor.
-
Check wiring continuity.
-
Replace sensor if open internally.
Common Fixes by Vehicle
What techs usually find when diagnosing P0118 on specific vehicles — tap your vehicle for the fix and the exact part:
2003-2014 GM 3.6L/5.3L/6.0L (Silverado, Impala, Tahoe) Easy DIY
ECT circuit high voltage — sensor open-circuit or disconnected. Replace the ECT sensor and inspect connector for pushed-out pins. Verify 5V reference at the signal wire with the connector unplugged (should read 4.8-5.0V).
Labor: 30-45 min2005-2015 Honda Accord/Civic/CR-V/Pilot Easy DIY
ECT high voltage after cooling system service — common when the sensor connector isn't fully seated. Reseat, clip, and monitor with a scan tool. If voltage still shows 5V, replace the sensor.
Labor: 30 min2004-2014 Ford F-150/Expedition 4.6L/5.4L Moderate DIY
Cylinder head temperature sensor (CHT, Ford uses this instead of ECT) reads open-circuit. Located under the intake manifold on some V8s — check wiring harness routing before condemning. Replace with Motorcraft CHT sensor.
Labor: 1-2 hrFrequently Asked Questions
My temperature gauge reads stone cold even though the engine is warm -- is this P0118?
Possibly. A high ECT input (open circuit) causes the ECU to assume maximum cold temperature, which may drive the gauge to cold. It may also cause a rich running condition on startup since the ECU thinks it is always cold.
Sources
This page is built from documented references. Verify against your own service info before repair work.
P0118 on Diesel, EV & Equipment
The same code ID appears across other engines and platforms. The diagnostic flow varies by manufacturer — these are the platform-specific breakdowns:
See All Codes & Fixes for Your Vehicle
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