P0117 on Subaru
Engine Coolant Temperature Sensor Circuit Low
P0117 on Subaru vehicles indicates engine coolant temperature sensor circuit low. Au7o has documented this code across 1 Subaru model — most commonly on Forester. This code means the engine coolant temperature (ECT) sensor is reading too low a voltage, which the computer interprets as an impossibly high coolant temperature. In most cases this is an electrical fault — such as a short to ground in the wiring — rather than the engine actually overheating. The coolant temperature signal affects fuel mixture, cooling fans, and other functions, so a bad reading can cause poor running, hard starting, or fans running constantly. The fault is usually in the sensor or its wiring. Typical repair costs on Subaru range from $1,800 to $3,500, depending on the specific model and root cause.
Common Causes of P0117
- •Faulty engine coolant temperature sensor
- •Short to ground in the sensor signal wire
- •Damaged or corroded wiring/connector at the sensor
- •Coolant contamination affecting the sensor
- •Poor electrical ground
- •Faulty PCM/ECM (less common)
P0117 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 P0117 mean on Subaru?▼
P0117 stands for "Engine Coolant Temperature Sensor Circuit Low." This code means the engine coolant temperature (ECT) sensor is reading too low a voltage, which the computer interprets as an impossibly high coolant temperature. In most cases this is an electrical fault — such as a short to ground in the wiring — rather than the engine actually overheating. The coolant temperature signal affects fuel mixture, cooling fans, and other functions, so a bad reading can cause poor running, hard starting, or fans running constantly. The fault is usually in the sensor or its wiring. On Subaru specifically, this code is documented across 1 model.
What causes P0117 on Subaru vehicles?▼
Common causes on Subaru: Faulty engine coolant temperature sensor, Short to ground in the sensor signal wire, Damaged or corroded wiring/connector at the sensor, Coolant contamination affecting the sensor, Poor electrical ground. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0117 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 P0117 documented?▼
Au7o has documented P0117 on 1 Subaru model: Forester.