P0118: Engine Coolant Temperature Sensor Circuit High
4 vehicles · 4 makes · $30-$7,000 repair
Most Reported On
P0118 is an OBD-II diagnostic trouble code meaning “Engine Coolant Temperature Sensor Circuit High.” P0118 indicates the engine coolant temperature (ECT) sensor circuit is reading abnormally high voltage, which the computer interprets as an implausibly cold coolant temperature. The ECT sensor changes resistance with temperature and tells the PCM how hot the engine is so it can manage fuel, the cooling fans, and the gauge. High voltage on this circuit usually points to an open circuit or a sensor reporting an unrealistically low temperature. The car may run rich, struggle to enter closed-loop operation, idle poorly, or show an inaccurate temperature gauge. This code is most commonly reported on 2009-2019 Ford Flex, 1998-2010 Subaru Forester, and 1996-2001 Audi A4, plus 1 other vehicle, with repair costs ranging from $30 to $7,000.
Common Causes
Typical Repair Cost
Based on 4 documented vehicle-specific issues. Actual cost depends on root cause and vehicle.
Diagnostic Tools
To diagnose P0118, you'll need an OBD-II scanner. Here are our recommendations at every price point.
ANCEL AD310 Classic OBD-II Scanner
by ANCEL
A simple, affordable code reader that reads and clears check engine codes. Great for quick diagnostics on any OBD-II vehicle (1996+).
- Read & clear engine codes
- View freeze frame data
- I/M readiness status
- No batteries or app needed
BlueDriver Pro Bluetooth Scanner
by BlueDriver
Bluetooth OBD-II scanner with a free companion app. Provides enhanced diagnostics, smog readiness, and repair reports sourced from a database of verified fixes.
- Enhanced diagnostics (ABS, SRS, transmission)
- Repair Reports with verified fixes
- Smog check readiness
- Free app (iOS & Android)
LAUNCH CRP123X OBD-II Scanner
by LAUNCH
A professional-grade handheld scanner that reads all four major systems (engine, transmission, ABS, SRS) with live data streaming and graphing.
- Engine, transmission, ABS, SRS diagnostics
- Live data stream & graphing
- AutoVIN for vehicle identification
- Free lifetime updates via Wi-Fi
Autel MaxiCOM MK808S Diagnostic Tool
by Autel
Shop-level diagnostic tablet with bi-directional control, active tests, and full system coverage. Ideal for serious DIYers and small shops.
- All-system diagnostics (25+ modules)
- Bi-directional control & active tests
- Oil reset, EPB, BMS, TPMS, injector coding
- 7-inch touchscreen with Android OS
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Vehicles Affected (4)
FAQ
What does P0118 mean?
P0118 stands for "Engine Coolant Temperature Sensor Circuit High." P0118 indicates the engine coolant temperature (ECT) sensor circuit is reading abnormally high voltage, which the computer interprets as an implausibly cold coolant temperature. The ECT sensor changes resistance with temperature and tells the PCM how hot the engine is so it can manage fuel, the cooling fans, and the gauge. High voltage on this circuit usually points to an open circuit or a sensor reporting an unrealistically low temperature. The car may run rich, struggle to enter closed-loop operation, idle poorly, or show an inaccurate temperature gauge.
What are the most common causes of P0118?
The most common causes of P0118 are: Faulty (open) engine coolant temperature sensor, Open or broken wire in the ECT signal circuit, Loose, corroded, or disconnected sensor connector, Poor ground or open in the sensor return circuit, Damaged wiring harness near the sensor, Corrosion in the connector terminals, Failed PCM input (rare). The specific cause varies by vehicle.
How much does it cost to fix P0118?
Repair costs for P0118 range from $30 to $7,000, depending on the vehicle and root cause.
Which vehicles are affected by P0118?
Au7o has documented P0118 across 4 vehicle models from 4 manufacturers: Audi, Ford, Subaru, Toyota.
Sources (6)
- owner-reportHow A Bad Water Pump Design Can Total A Ford Flex — The Autopian
- mediaSubaru Model Years Worst Affected By Head Gasket Problems - Jalopnik
- ForumEJ25 head gasket failure inevitable - Subaru Forester Owners
- mediaSubaru Head Gasket Problems - Mechanic Base
- ForumGuide on how to replace a G62 Coolant Temperature Sensor - Audifans.net
- ForumCoolant Sensor, Updated Green, G62 (ELTH-OEM) - JH Motorsports
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.