P1115
GMEngine Coolant Temperature (ECT) Sensor Circuit Intermittent High Voltage/Intake Air Temperature (IAT) - B Circuit High Input
Medium SeverityThis code indicates an intermittent high voltage signal from either the Engine Coolant Temperature (ECT) sensor or the Intake Air Temperature (IAT) sensor B circuit, which the Powertrain Control Module (PCM) interprets as extremely cold temperatures. This can lead to the engine running rich, impacting fuel efficiency and emissions.
⚠️ Before You Begin (Safety First)
Always ensure the engine is cool before working on coolant systems. Disconnect the negative battery terminal before performing any electrical work. Be cautious around hot engine components and moving parts.
Common Symptoms
- Check Engine Light illumination
- Poor fuel economy
- Engine running rich
- Rough idle
- Hard starting, especially when cold
- Black smoke from exhaust
Common Causes
- Faulty Engine Coolant Temperature (ECT) sensor
- Faulty Intake Air Temperature (IAT) sensor
- Corroded or damaged wiring or connectors in the ECT or IAT circuit
- Open circuit in the ECT or IAT sensor wiring
- Malfunctioning Powertrain Control Module (PCM) - less common
Frequently reported on: Chevrolet Silverado 2000-2006, GMC Sierra 2000-2006, Pontiac Grand Am 1999-2005, Saturn S-Series 1996-2002, Chevrolet Cavalier 1996-2005
Diagnostic Steps
- Visually inspect the Engine Coolant Temperature (ECT) sensor and Intake Air Temperature (IAT) sensor for any signs of damage or corrosion.
- Check the wiring harness and connectors leading to both the ECT and IAT sensors for frayed wires, loose connections, or corrosion.
- Test the resistance of the ECT and IAT sensors using a multimeter; compare readings to manufacturer specifications at various temperatures.
- Ensure proper coolant level in the engine.
- Clear the code with an OBD-II scanner after performing repairs and test drive the vehicle to see if the code returns.
👨🔧 When to Call a Professional
If you have replaced the sensor and checked for obvious wiring issues, but the code persists or is truly intermittent and hard to diagnose, it's time to consult a professional mechanic. Advanced diagnostic tools are often required to pinpoint intermittent electrical faults.
Commonly Asked Questions
What does 'High Voltage' mean for a temperature sensor?
For most temperature sensors (thermistors), high voltage indicates very low resistance, which the PCM interprets as an extremely cold temperature, or an open circuit within the sensor or wiring.
Can I drive with a P1115 code?
While you may be able to drive, it's not recommended for long. The engine may run rich, leading to decreased fuel economy, increased emissions, and potential damage to catalytic converters over time. Address it as soon as possible.
How do I test the ECT or IAT sensor?
You can test these sensors by measuring their resistance with a multimeter while the engine is cold and then again after it warms up. The resistance should change significantly according to the manufacturer's specifications. High voltage at the PCM side when the sensor is disconnected usually indicates an open circuit, while consistently high voltage with sensor connected usually points to sensor failure or a wiring short to voltage.
Is P1115 the same as a P0110 or P0115 code?
P1115 is a manufacturer-specific code (GM in this case) that points to an intermittent high voltage condition, affecting either the ECT or IAT circuit. P0110 (IAT Circuit Malfunction) and P0115 (ECT Circuit Malfunction) are generic codes that indicate a general issue with those circuits, not specifically an intermittent high voltage condition.
Why is 'intermittent' important for this code?
An intermittent fault means the problem is not constant, making it harder to diagnose. The sensor or wiring might be failing only under specific conditions, like vibrations or temperature changes. It often requires more thorough testing than a constant fault.