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
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 an OE-quality Motorcraft unit CHT sensor. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.
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.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
-
Check ECT signal voltage: above 4.7V at operating temperature indicates an open circuit.
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Disconnect and reconnect the ECT connector. If the fault clears, the connector was loose.
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Measure sensor resistance at operating temperature. Should be 200-300 ohms when hot. Infinite resistance indicates open sensor.
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Check wiring continuity.
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Replace sensor if open internally.
Sources 2
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
- Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition
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:
Commonly Affected Vehicles
- Ford F-150 and Expedition
- Dodge Ram
- Toyota 4Runner
- Honda Pilot
- Chevrolet Tahoe
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