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
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.
-
Inspect wiring for chafing or contact with the engine block.
-
Clean the connector and retest before replacing the sensor.
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 minFrequently 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.
Sources
This page is built from documented references. Verify against your own service info before repair work.
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:
See All Codes & Fixes for Your Vehicle
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