What is SPN 91
SPN 91: Refers to a fault related to the engine coolant temperature sensor, which monitors the temperature of the engine coolant. This sensor is essential for regulating the engine’s cooling system and ensuring optimal engine performance.
When SPN 91 is triggered, it means that the ECM is receiving incorrect or out-of-range data from the engine coolant temperature sensor, which could lead to engine overheating, underperformance, or even engine damage if not addressed promptly.
Why It Happened
This fault code can occur due to several reasons:
- Low coolant levels: Insufficient coolant in the system can cause the sensor to read abnormal temperatures.
- Malfunctioning coolant temperature sensor: The sensor may fail or become damaged over time, providing incorrect readings.
- Wiring issues: Damaged or corroded wiring between the sensor and the ECM can result in improper signal transmission.
- Coolant contamination: Contaminants in the coolant can affect the sensor’s ability to provide accurate readings.
- Faulty thermostat: A malfunctioning thermostat can prevent proper coolant flow, leading to abnormal temperature readings.
How to Resolve It
To resolve SPN 91:
- Check coolant levels: Ensure that the coolant is at the proper level and top off if necessary.
- Inspect the sensor: Test the engine coolant temperature sensor for malfunctions and replace it if needed.
- Check wiring: Inspect the wiring and connections between the coolant temperature sensor and ECM for any damage, corrosion, or loose connections.
- Test thermostat: Ensure the thermostat is functioning correctly and regulating coolant flow.
- Clear the fault code: After addressing the issue, clear the fault code and restart the engine to confirm the fix.
How to Avoid Before It Happens
To prevent SPN 91:
- Regularly check coolant levels and inspect the cooling system for leaks.
- Perform routine maintenance on the coolant temperature sensor and wiring.
- Use tools like Clue to monitor engine temperature in real-time for early alerts on coolant system or sensor issues.
