P1115
ToyotaEngine Coolant Temperature (ECT) Sensor Circuit Intermittent High Voltage/IAT - B Circuit High Input. This indicates that the Engine Control Unit (ECU) has detected an intermittent high voltage signal from the Engine Coolant Temperature sensor circuit.
Medium SeverityThe Engine Control Unit (ECU) is receiving an inconsistent and abnormally high voltage signal from the Engine Coolant Temperature (ECT) sensor, suggesting an electrical fault within the sensor or its wiring. This can lead to incorrect fuel mixture calculations, impacting engine performance, fuel economy, and potentially causing drivability issues.
⚠️ Before You Begin (Safety First)
Always allow the engine to cool completely before working on the cooling system to prevent severe burns from hot coolant or engine components. Disconnect the negative battery terminal before performing any electrical work to avoid accidental short circuits or electrical shock.
Common Symptoms
- Check Engine Light (CEL) illumination
- Poor fuel economy
- Rough idling or stalling
- Engine running rich (excessive fuel) or lean (insufficient fuel)
- Difficulty starting, especially when the engine is cold
- Engine overheating (if the ECU receives a false low-temperature reading)
- Cooling fans running constantly or not at all
- Erratic temperature gauge readings
Common Causes
- Faulty Engine Coolant Temperature (ECT) sensor
- Corroded, loose, or damaged electrical connections at the ECT sensor or its harness
- Damaged, frayed, or shorted wiring in the ECT sensor signal circuit (short to voltage)
- Open circuit within the ECT sensor wiring
- Faulty Engine Control Unit (ECU) (less common)
Frequently reported on: Toyota Camry (1998-2006), Toyota Corolla (1998-2008), Toyota Tacoma (1998-2004), Toyota 4Runner (1998-2002), Toyota Sienna (1998-2003)
Diagnostic Steps
- Locate the Engine Coolant Temperature (ECT) sensor, typically found screwed into the engine block or cylinder head, often near the thermostat housing.
- Carefully inspect the electrical connector and the wiring leading to the ECT sensor for any signs of damage, corrosion, or loose connections. Clean any corrosion found.
- With the engine off and cooled, disconnect the ECT sensor's electrical connector. Use a multimeter to test the resistance across the sensor's terminals and compare it to manufacturer specifications for varying temperatures. Also, check for continuity in the wiring harness.
- Test the voltage at the ECT sensor connector (with the ignition on, engine off) to ensure proper reference voltage and ground are present, referring to a wiring diagram for correct pin identification.
- If the sensor tests faulty or if wiring damage is confirmed, disconnect the negative battery terminal. Replace the ECT sensor or repair the damaged wiring harness as necessary. Be prepared to catch and properly dispose of any coolant that drains.
- After replacement or repair, refill and bleed the cooling system according to manufacturer procedures if coolant was lost.
- Reconnect the battery, use an OBD-II scanner to clear the P1115 trouble code, and then perform a test drive to confirm the repair and ensure the code does not return.
👨🔧 When to Call a Professional
If replacing the Engine Coolant Temperature (ECT) sensor and inspecting the wiring does not resolve the P1115 code, or if you suspect more complex electrical issues or an internal Engine Control Unit (ECU) fault, it is best to consult a professional automotive technician for further diagnosis.
Commonly Asked Questions
Can I drive my Toyota with a P1115 code?
It is not recommended to drive for extended periods with a P1115 code. While the car might run, the incorrect temperature readings can lead to poor fuel economy, engine performance issues, and potentially cause engine overheating or damage over time.
What does 'intermittent high voltage' mean for the ECT sensor?
It means the sensor's signal wire is occasionally reporting a voltage that is higher than expected, indicating a possible internal fault within the sensor, a short to voltage in the wiring, or a poor electrical connection causing erratic readings.
Where is the ECT sensor typically located on a Toyota?
On most Toyota engines, the Engine Coolant Temperature (ECT) sensor is commonly found threaded into the engine block or cylinder head, often near the thermostat housing or on an intake manifold runner, where it can directly measure coolant temperature.
Do I need to drain all the coolant to replace the ECT sensor?
You typically need to drain some coolant, but not necessarily all of it. The sensor is submerged in coolant, so be prepared for some coolant loss when removing it. Have a drain pan ready and be prepared to top off and bleed the cooling system afterwards.
Could other issues cause P1115, like a bad thermostat?
While a bad thermostat affects engine temperature, P1115 specifically indicates an electrical circuit issue (intermittent high voltage) with the ECT sensor itself or its wiring. A faulty thermostat would likely trigger different diagnostic trouble codes related to engine temperature regulation, not directly the sensor's electrical signal.