Here's a breakdown:
* Closed-Loop Fuel Control: This is the optimal mode for fuel injection. The O2 sensor monitors the exhaust gases, sending information back to the PCM. The PCM then adjusts the fuel mixture to maintain the ideal air/fuel ratio for efficient combustion and minimal emissions.
* Insufficient Coolant Temperature: The PCM needs the engine to reach a certain operating temperature (usually around 170-190°F or 77-88°C) before it switches to closed-loop control. At lower temperatures, the engine's operation is less stable, and the O2 sensor readings might be inaccurate.
Why this happens:
* Thermostat: The most common culprit. A stuck-open thermostat prevents the engine from reaching its optimal operating temperature. The coolant constantly circulates without being warmed sufficiently.
* Coolant Leak: A leak in the cooling system reduces the coolant level, hindering the engine's ability to reach and maintain the proper temperature.
* Faulty Coolant Temperature Sensor (CTS): The CTS measures the coolant temperature and sends this information to the PCM. If the sensor is faulty, it might report an incorrect temperature, preventing the switch to closed-loop.
* Water Pump: A failing water pump might not circulate coolant efficiently, resulting in insufficient heating.
* Low Coolant Level: Simply not having enough coolant in the system will prevent it from heating up properly.
What to do:
1. Check your coolant level: Make sure the coolant is at the correct level in the radiator's overflow tank. If it's low, carefully add 50/50 mix of coolant and distilled water (never just plain water).
2. Check for leaks: Inspect the radiator, hoses, water pump, and engine block for any signs of leaks.
3. Check the thermostat: A simple way to test this is to feel the upper radiator hose when the engine is running and at operating temperature. If it's cool, the thermostat is likely stuck open. It's relatively inexpensive and easy to replace.
4. Inspect the coolant temperature sensor (CTS): This sensor is usually located in the engine block or cylinder head. A visual inspection for damage is a good start. A more thorough check may require a multimeter to test its resistance at different temperatures (consult a repair manual for specific readings).
5. Check the water pump: Look and listen for any unusual noises coming from the water pump. A failing water pump can make unusual whining sounds.
Important Note: Driving with insufficient coolant can cause serious engine damage. If you notice any overheating symptoms (steam from the hood, overheating gauge warning), stop driving immediately to avoid costly repairs.
If you're not comfortable performing these checks yourself, it's best to take your Lumina to a qualified mechanic for diagnosis and repair. They can properly diagnose the problem and fix it safely.
