Subaru Legacy Engine Coolant Temperature Sensor Guide (2010-2022)
Everything you need to know about replacing the Engine Coolant Temperature Sensor on your 2010-2022 Subaru Legacy.
- A failing ECT sensor on a Subaru Legacy can cause a check engine light, poor fuel economy, overheating, and rough running.
- For 2020-2022 models, check for issues with the Thermo Control Valve (TCV), which has an extended warranty and can cause similar symptoms.
- Replacement is a simple, low-cost DIY job for most owners, requiring basic tools and about 30 minutes.
- Choosing a quality aftermarket brand like Standard Ignition or Beck Arnley is a reliable alternative to a more expensive OEM part.
Symptoms of a Failing ECT Sensor in a Subaru Legacy
A bad Engine Coolant Temperature (ECT) sensor can cause a range of problems, from annoying to serious. Because the sensor provides critical data to the engine computer, a false signal can make the engine behave as if it's either colder or hotter than it actually is. Here are the most common signs of failure for a 2010-2022 Subaru Legacy:
- Check Engine Light: This is often the first sign. The ECU will detect a voltage reading from the sensor that is outside the normal range and trigger a fault code. Common codes include P0117 (circuit low), P0118 (circuit high), and P0128 (thermostat rationality).
- Poor Fuel Economy: If the sensor incorrectly tells the ECU the engine is cold, the computer will enrich the fuel mixture, causing the car to use more gas than necessary.
- Black Smoke from Exhaust: A very rich fuel mixture can result in unburnt fuel exiting through the exhaust, which looks like black smoke.
- Engine Overheating or Fans Not Working: If the sensor fails to report that the engine is hot, the ECU won't know to turn on the cooling fans. This can lead to overheating, especially in stop-and-go traffic.
- Rough Idle and Poor Performance: Incorrect fuel and timing adjustments can cause the engine to run rough, hesitate, or feel sluggish.
- Hard Starting: The engine may be difficult to start, particularly when it's already warm, because the fuel mixture is incorrect for the actual engine temperature.
Special Note for 2019-2022 Models: The Thermo Control Valve
For some newer Legacy models (specifically 2020-2022), issues that seem like a bad ECT sensor—like a dead temperature gauge and a check engine light—may actually be caused by a failing Thermo Control Valve (TCV). This integrated unit contains a sensor, and failures have been common enough that Subaru issued a Technical Service Bulletin (TSB 09-80-21R) and extended the warranty on this part to 15 years or 150,000 miles. If you have a newer Legacy, it's crucial to have the codes read by a professional to determine if the TCV is the actual problem, as it may be covered by warranty.
Choosing the Right Aftermarket ECT Sensor
When replacing the ECT sensor, you have a choice between the original equipment (OEM) part from Subaru and various aftermarket brands. For a simple sensor like this, a quality aftermarket part can offer significant savings without sacrificing reliability.
Here's a breakdown of the available brands:
- Premium Aftermarket (Good): Brands like Standard Ignition (SMP) and Beck Arnley have a long-standing reputation for producing quality replacement parts that often meet or exceed OE specifications. They focus on form, fit, and function, making them a reliable choice.
- Standard Aftermarket (Better): Brands such as Walker Products, Four Seasons, and Holstein are solid mid-tier options. They produce a wide range of sensors and are a common choice for general repairs, offering a good balance of price and quality.
- Budget-Friendly (Basic): Brands like Facet and Global Parts often fall into the more budget-oriented category. While they are the most affordable, some forum discussions suggest that for critical sensors, it's often better to stick with a more established brand to avoid premature failure or inaccurate readings.
Pro Tip: Many Subaru enthusiasts prefer to use OEM parts for critical sensors. However, if choosing aftermarket, sticking to a reputable brand like Standard or Beck Arnley is a safe bet. Some users have reported issues with budget sensors providing inaccurate readings, which can cause persistent running problems.
Cost of Replacing a Subaru Legacy ECT Sensor
The cost to replace the ECT sensor is relatively low, especially if you do the work yourself. The part itself is inexpensive, and the job is straightforward for most DIY mechanics.
| Item | Estimated Cost |
|---|---|
| New Aftermarket ECT Sensor | $14.51 - $55.50 |
| New OEM Subaru ECT Sensor | $50 - $77 |
| Shop Labor | $75 - $150 |
| DIY Total | $14.51 - $55.50 |
| Shop Total | $90 - $227 |
Frequently Asked Questions (FAQ)
Where is the ECT sensor located on a 2010-2022 Subaru Legacy?
On most 2.5L Subaru engines from this era, the ECT sensor is located on the coolant crossover pipe, which sits on top of the engine block toward the front. It's typically a brass sensor with a plastic electrical connector. On some later models, there may be two temperature sensors, or the primary sensor may be part of the larger Thermo Control Valve assembly.
Can I replace the ECT sensor myself?
Yes, this is a very DIY-friendly job for most models. The sensor is usually accessible from the top of the engine. The process involves disconnecting the battery, unplugging the sensor, and using a deep socket wrench to unscrew the old sensor and install the new one. A small amount of coolant will leak out, so be prepared with a rag and have the new sensor ready to install quickly. Always ensure the engine is completely cool before starting.
Do I need to drain the coolant to replace the sensor?
You don't need to drain the entire cooling system. The sensor is located high on the engine, so only a small amount of coolant will spill when you remove it. To minimize the mess, you can unscrew the old sensor and quickly plug the hole with the new one. It's also a good idea to have the new sensor's threads pre-wrapped with Teflon tape or sealant if it's not pre-applied.
Are there any recalls for the ECT sensor on the Subaru Legacy?
There are no direct recalls for the standalone Engine Coolant Temperature Sensor on the 2010-2022 Subaru Legacy. However, there is a significant warranty extension for the Thermo Control Valve (TCV) on 2020-2022 models, which contains a temperature sensor and is a known failure point. There is also a recall for some 2020-2022 models related to an Occupant Detection System (ODS) sensor, but this is unrelated to the engine cooling system.
Helpful Videos
Technical Specifications
OEM Part Numbers: 22630AA161 22630AA17A 22630AA230 22630AA27A
The ECT sensor is a two-wire thermistor that screws into a coolant passage on the engine. Its resistance decreases as coolant temperature increases, altering a 5-volt reference signal sent from the ECU.
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
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