Engine Coolant Temperature Sensor 1 Circuit Low Input
The P0117 code means the vehicle's onboard diagnostic system has detected: Engine Coolant Temperature Sensor 1 Circuit Low Input. This is a moderate severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- easy
- Estimated cost
- $15-$50
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Common Symptoms
- Check Engine Light on
- Engine runs rich
- Possible black smoke
- Poor fuel economy
- Cooling fan may run continuously
Probable Causes (Ranked by Likelihood)
- ECT sensor shorted to ground internally Very High
- Short to ground in ECT signal wiring High
- Corroded sensor connector bridging signal and ground Moderate
Common Fixes by Vehicle
What techs usually find when diagnosing P0117 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 sensor circuit low voltage — usually shorted sensor or signal wire pinched. Replace ECT sensor first (cheap and typical cause). If code returns, backprobe the signal pin at PCM for a short to ground.
Labor: 30-45 min2001-2015 Honda Accord/Civic/CR-V 1.8L/2.0L/2.4L Easy DIY
Honda ECT circuit low — replace the ECT sensor (near the upper radiator hose) with Honda OEM. If the code persists, check for coolant intrusion into the connector causing a short.
Labor: 30 min2005-2014 Ford F-150/Escape 3.5L/5.0L Easy DIY
ECT voltage low — replace the Motorcraft ECT sensor. On EcoBoost engines, also check the secondary coolant temp sensor as both may be combined or separate depending on year.
Labor: 30-45 min
Frequently Asked Questions
A low ECT input makes the ECU think the engine is very hot -- what happens?
The ECU cuts the cold-start enrichment and may run a lean mixture. Interestingly, a shorted ECT often also keeps the radiator fan running at all times since the ECU thinks it is overheating.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
-
Check ECT voltage: below 0.3V at any temperature indicates a short to ground.
-
Disconnect the sensor. If voltage rises to 5V at the PCM side, the sensor is faulty.
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Inspect wiring for chafing or contact with the engine block.
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Clean the connector and retest before replacing the sensor.
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
P0117 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
- Honda Civic (1996-2005)
- Toyota Corolla
- Nissan Sentra
- Chevrolet Cavalier
- Ford Escort
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