Here are a few possible reasons why the check engine light is on in your Toyota Highlander with 37,000 miles, despite replacing the air filter and PCV valve:
1. Oxygen Sensor: A faulty oxygen sensor can affect the vehicle's air-fuel ratio, leading to the check engine light coming on. The oxygen sensor measures the amount of unburned oxygen in the exhaust gases and sends this information to the engine control unit (ECU) to adjust the fuel injection accordingly. If the sensor is not functioning properly, it can cause the engine to run inefficiently and trigger the check engine light.
2. Spark Plugs: Worn-out or fouled spark plugs can also cause the check engine light to turn on. Spark plugs are responsible for igniting the air-fuel mixture in the engine's combustion chambers. Over time, spark plugs can become worn or develop deposits, which can affect their ability to ignite the fuel efficiently. This can result in incomplete combustion, leading to the illumination of the check engine light.
3. Fuel Injector Issues: Malfunctioning fuel injectors can cause the engine to receive an improper amount of fuel, resulting in rough idling, hesitation, or stalling. In some cases, faulty fuel injectors can also trigger the check engine light to come on.
4. Catalytic Converter: The catalytic converter is responsible for reducing harmful emissions from the vehicle's exhaust system. If the catalytic converter becomes damaged or clogged, it can cause the check engine light to illuminate.
5. Vacuum Leaks: Vacuum leaks in the engine can affect its performance and cause the check engine light to come on. Vacuum leaks can occur in various components, such as hoses, gaskets, or vacuum lines, leading to a loss of vacuum pressure in the engine.
6. EGR Valve: The EGR (Exhaust Gas Recirculation) valve is designed to reduce emissions by recirculating a portion of the exhaust gases back into the engine. If the EGR valve becomes stuck or malfunctions, it can cause the check engine light to come on.
To determine the exact cause of the check engine light, it's recommended to have the vehicle diagnosed by a qualified mechanic or a Toyota dealership. They will be able to use diagnostic tools to read the trouble codes stored in the vehicle's computer and identify the specific issue that is causing the check engine light to illuminate. Once the root cause is identified, appropriate repairs or replacements can be made to resolve the problem and turn off the check engine light.
It's worth noting that while replacing the air filter and PCV valve are regular maintenance tasks, they may not necessarily be the cause of the check engine light. The check engine light is a warning indicator that there is an underlying issue that requires attention, and it's important to address it promptly to ensure the efficient and reliable operation of your vehicle.
