Fuel & air metering · Powertrain · generic (SAE-defined)
P0117: Engine Coolant Temperature Circuit Low
P0117 means the engine coolant temperature (ECT) sensor signal voltage is lower than expected, so the engine computer sees an unrealistically hot coolant reading.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0117 sets
The engine coolant temperature (ECT) sensor's resistance falls as coolant heats up, lowering the signal voltage seen by the powertrain control module (PCM). If the voltage drops below the lowest plausible value for a set time, P0117 sets. A shorted sensor or a signal wire shorted to ground is the usual cause, though a genuinely overheated engine should always be ruled out.
Common causes of P0117
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Internally shorted ECT sensor
- Signal wire shorted to ground
- Coolant or water in the connector
- Actual engine overheating in rare cases
- PCM fault (rare)
P0117 symptoms
- Check engine light on
- Temperature gauge reading very high
- Cooling fans running constantly
- Hard starting when cold
- Lean running or hesitation on cold starts
How P0117 is diagnosed
- Confirm actual engine temperature with an infrared thermometer and check coolant level
- Scan for codes and view the ECT value in live data
- Unplug the sensor; the reading should drop to a very cold value if wiring is good
- Inspect the connector for coolant contamination
- Check the signal wire for a short to ground
- Measure sensor resistance and replace if out of specification
Typical fixes for P0117
- Replace the ECT sensor
- Repair a wire shorted to ground
- Replace a contaminated connector
- Repair the cooling system if the engine is truly overheating
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Manufacturer notes
Older definitions read "Engine Coolant Temperature Circuit Low Input". Definitions can vary by manufacturer; check factory service information.
Related codes & warning lights
P0117 FAQ
What does code P0117 mean?
P0117 means the engine coolant temperature (ECT) sensor signal voltage is lower than expected, so the engine computer sees an unrealistically hot coolant reading. The standard definition is "Engine Coolant Temperature Circuit Low."
Can I drive with a P0117 code?
Short drives are generally possible, but verify the engine is not actually overheating. If the gauge reads high, coolant is boiling or there is steam, stop and turn the engine off; otherwise get the sensor circuit checked soon.
Does P0117 mean my engine is overheating?
Usually it means the sensor or wiring is reporting a falsely hot value, but always confirm actual temperature before driving further.
Why would the engine be hard to start cold with P0117?
The PCM believes the engine is hot and supplies too little fuel for a cold start.
Keep researching
Engine guides by brand (known issues, specs)
More fuel & air metering codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
- California Air Resources Board — On-Board Diagnostic (OBD) Program
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.