P0118 on Subaru
Engine Coolant Temperature Sensor Circuit High
P0118 on Subaru vehicles indicates engine coolant temperature sensor circuit high. Au7o has documented this code across 1 Subaru model — most commonly on Forester. 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. Typical repair costs on Subaru range from $1,800 to $3,500, depending on the specific model and root cause.
Common Causes of P0118
- •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)
P0118 on Subaru by Model
Subaru Forester(1 issue)
- EJ25 Head Gasket Failure (External Leak)1998-2010
The EJ25 2.5L horizontally-opposed engine in 1998-2010 Foresters is notorious for external head gasket failure. Unlike typical blown head gaskets that cause overheating, the Subaru EJ25 gaskets fail externally, leaking coolant and oil down the sides of the engine. The failure is caused by the gasket material (composite) breaking down over time, combined with the horizontal orientation placing uneven stress on the gaskets. This is widely considered the most common and well-documented Subaru defect.
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What does P0118 mean on Subaru?▼
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. On Subaru specifically, this code is documented across 1 model.
What causes P0118 on Subaru vehicles?▼
Common causes on Subaru: 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. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0118 on a Subaru?▼
Repair costs on Subaru range from $1,800 to $3,500, depending on the specific model and root cause.
Which Subaru models have P0118 documented?▼
Au7o has documented P0118 on 1 Subaru model: Forester.