P1115
SubaruEngine Coolant Temperature (ECT) Sensor Circuit Intermittent High Voltage/IAT - B Circuit High Input
Medium SeverityThis diagnostic trouble code indicates an intermittent high voltage condition in the Engine Coolant Temperature (ECT) sensor circuit or a high input from the Intake Air Temperature (IAT) sensor 'B' circuit. This can lead to the engine receiving incorrect temperature information, causing issues with fuel delivery, poor performance, reduced fuel economy, or difficulty starting.
⚠️ Before You Begin (Safety First)
Always allow the engine to cool down completely before working on any part of the cooling system to prevent severe burns. Be cautious when disconnecting electrical connectors near hot engine components or moving parts. For any electrical work, disconnect the battery's negative terminal to prevent accidental shorts or shocks.
Common Symptoms
- Check Engine Light illumination
- Engine running rich or lean
- Poor fuel economy
- Engine difficult to start when cold or hot
- Rough idle
- Engine may overheat (gauge might not be accurate)
- Reduced engine performance
- Hesitation or stalling
Common Causes
- Faulty Engine Coolant Temperature (ECT) sensor
- Faulty Intake Air Temperature (IAT) sensor
- Corroded, loose, or damaged electrical connectors for the ECT or IAT sensor
- Damaged wiring harness (frayed, shorted, or open circuit) affecting the sensor circuits
- Low engine coolant level preventing accurate ECT readings
- Faulty Powertrain Control Module (PCM) (rare)
Frequently reported on: Subaru Forester (2000-2008), Subaru Impreza (1998-2007), Subaru Legacy (1999-2004), Subaru Outback (2000-2004), Subaru WRX (2002-2005)
Diagnostic Steps
- Visually inspect the wiring harnesses and electrical connectors for both the Engine Coolant Temperature (ECT) sensor and the Intake Air Temperature (IAT) sensor for any signs of damage, fraying, corrosion, or looseness.
- Ensure the engine coolant level is at the manufacturer's specified mark. Top off with the correct coolant type if necessary.
- Carefully disconnect the electrical connector from the ECT sensor, inspect the terminals for any corrosion or bending, and then firmly reconnect it.
- Similarly, disconnect the electrical connector from the IAT sensor, inspect its terminals, and firmly reconnect it.
- If visual inspection does not reveal any obvious issues and the code persists, use a multimeter to test the resistance of both the ECT and IAT sensors. Compare the readings to your vehicle's service manual specifications at various temperatures.
- If either sensor's resistance falls outside of the specified range, replace the faulty sensor.
- After performing any repairs or replacements, use an OBD-II scanner to clear the P1115 diagnostic trouble code from the PCM and monitor if the code returns during subsequent driving cycles.
- Perform a drive cycle to confirm the repair and ensure the code does not reappear.
- If possible, check for vacuum leaks that could affect engine performance and sensor readings.
👨🔧 When to Call a Professional
If, after inspecting the wiring and replacing the suspected sensor, the P1115 code continues to appear intermittently, or if engine performance issues are severe and persist, it is highly advisable to consult a professional mechanic. Intermittent electrical faults can be complex to diagnose without specialized diagnostic equipment and expertise.
Commonly Asked Questions
Can I drive with a P1115 code?
Driving with a P1115 code is not recommended for extended periods. While your car might seem to run, inaccurate temperature readings can lead to poor fuel economy, increased emissions, and potentially cause more significant engine damage over time if not addressed. It's best to diagnose and repair it promptly.
Where are the ECT and IAT sensors typically located on a Subaru?
The Engine Coolant Temperature sensor on most Subaru models is usually located on the engine block, near the thermostat housing, or in the cylinder head. The Intake Air Temperature sensor is generally found within the air intake ducting or the intake manifold. Specific locations can vary slightly by model and year, so consulting a service manual is advised.
Do I need special tools to fix a P1115 code?
An OBD-II scanner is essential for reading and clearing the P1115 code. A multimeter is highly recommended for accurately testing the resistance of both the ECT and IAT sensors. Beyond these, basic hand tools (wrenches, sockets, screwdrivers) are usually sufficient for sensor replacement.
What does 'intermittent' mean in the context of P1115?
'Intermittent' means that the high voltage condition or fault in the sensor circuit is not constant. It might only occur under specific engine operating conditions, at certain temperatures, or due to a loose electrical connection that temporarily breaks contact. This can make diagnosis more challenging than a constant fault.
Could a low coolant level cause the P1115 code?
Yes, an extremely low engine coolant level can prevent the Engine Coolant Temperature sensor from being fully immersed in coolant, leading to inaccurate temperature readings. This can sometimes cause the sensor to report an out-of-range value, potentially triggering codes like P1115.