P1117
SubaruEngine Coolant Sensor intermittent/ECT Sensor Intermittent
Medium SeverityThis code indicates that the Powertrain Control Module (PCM) is receiving an intermittent signal from the Engine Coolant Temperature (ECT) sensor. This can lead to incorrect fuel mixture adjustments, affecting engine performance and fuel efficiency.
⚠️ Before You Begin (Safety First)
Always ensure the engine is cool before working on the cooling system to prevent burns. Disconnect the negative battery terminal before working on electrical components to avoid electrical shock or damage. Use appropriate eye protection.
Common Symptoms
- Check Engine Light illumination
- Erratic temperature gauge readings
- Poor fuel economy
- Rough idle or stalling
- Engine running rich or lean
- Difficulty starting (especially when cold)
Common Causes
- Faulty or intermittent Engine Coolant Temperature (ECT) sensor
- Corroded or loose wiring/connector to the ECT sensor
- Damaged wiring harness
- Low engine coolant level (though less likely for "intermittent" specifically, it can affect sensor readings)
- Faulty Powertrain Control Module (PCM) (less common)
Frequently reported on: Subaru Forester (2000-2010), Subaru Impreza (2000-2010), Subaru Legacy (2000-2010), Subaru Outback (2000-2010), Subaru Baja (2003-2006)
Diagnostic Steps
- Ensure the engine is cool and visually inspect the ECT sensor and its wiring harness for any obvious damage, corrosion, or loose connections.
- Disconnect the ECT sensor connector and inspect the pins for corrosion or bends. Clean if necessary.
- Using a multimeter, test the resistance of the ECT sensor at different engine temperatures (if possible, compare to specifications) to check for intermittent readings.
- Check the wiring continuity from the ECT sensor connector back to the PCM connector.
- If the sensor tests faulty or the wiring is compromised, replace the ECT sensor.
- Refill and bleed the cooling system if coolant was drained during the replacement.
- Clear the P1117 code using an OBD-II scanner and test drive the vehicle to confirm the repair.
👨🔧 When to Call a Professional
If replacing the Engine Coolant Temperature sensor does not resolve the P1117 code, or if you suspect underlying wiring issues or PCM faults, it is best to consult with a professional automotive technician for a more in-depth diagnostic.
Commonly Asked Questions
What does P1117 mean for my Subaru?
P1117 indicates an intermittent signal from your engine's Engine Coolant Temperature (ECT) sensor, meaning the computer is getting inconsistent data about engine temperature.
Is it safe to drive with a P1117 code?
While not usually an immediate breakdown risk, an intermittent ECT sensor can cause poor fuel economy, emissions issues, and rough running. It's best to address it promptly.
Where is the ECT sensor located on a Subaru?
The ECT sensor is typically located near the thermostat housing on the engine, often screwed directly into the engine block or an intake manifold coolant passage.
Do I need to drain the coolant to replace the ECT sensor?
Yes, you will likely need to drain a small amount of coolant, or the entire system, depending on the sensor's location, to prevent spills during replacement.
Can a faulty thermostat cause a P1117 code?
While a faulty thermostat can affect engine temperature, P1117 specifically points to an intermittent sensor signal, not necessarily incorrect temperature itself. However, a thermostat issue could indirectly affect sensor readings.