Engine Coolant Temperature Sensor Circuit Intermittent High Voltage (GM)
What does P1115 mean?
The P1115 code means the vehicle's onboard diagnostic system has detected: Engine Coolant Temperature Sensor Circuit Intermittent High Voltage (GM). This is a moderate severity code.
Common Symptoms
- Check Engine Light on
- Engine runs lean when cold
- Extended warm-up time
- Cooling fans may not turn on properly
- Rough idle especially when cold
Probable Causes (Ranked by Likelihood)
- Defective engine coolant temperature (ECT) sensor Very High
- Open circuit in ECT sensor wiring High
- Loose or disconnected ECT sensor connector Moderate
- Corroded ECT sensor ground wire Moderate
- PCM fault Low
Step-by-Step Diagnostic Procedure
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Compare ECT sensor reading on scan tool with an infrared thermometer reading
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Inspect the ECT sensor connector for a secure fit and clean pins
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Check for an open circuit in the ECT sensor signal wire
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Measure ECT sensor resistance and compare to temperature-resistance chart
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Verify the sensor ground wire has good continuity to the PCM
Frequently Asked Questions
What is the difference between P1114 and P1115?
P1114 indicates intermittent low voltage (PCM thinks engine is hot), while P1115 indicates intermittent high voltage (PCM thinks engine is cold). Both point to a faulty ECT sensor or wiring issue.
Why are cooling fans affected by P1115?
The PCM uses the ECT sensor to control cooling fan operation. If the sensor reports that the engine is cold (high voltage), the PCM may not activate the fans when needed, potentially causing overheating.
How do I test the ECT sensor?
Remove the ECT sensor and place it in water. Heat the water while measuring resistance with a multimeter. Resistance should decrease smoothly as temperature rises. Compare readings to the manufacturer specifications.