Common Causes:
* Oxygen Sensor (O2 Sensor): This is one of the most frequent culprits. A failing O2 sensor can cause inaccurate fuel-air mixture readings, resulting in a check engine light.
* Mass Airflow Sensor (MAF Sensor): If the MAF sensor is dirty or faulty, it can't accurately measure the amount of air entering the engine, leading to an improper fuel mixture and the light illuminating.
* Crank Position Sensor (CPS): A faulty CPS can prevent the engine from getting the proper timing signal, causing misfires and triggering the check engine light.
* Engine Coolant Temperature Sensor (ECT Sensor): This sensor monitors the engine's coolant temperature. If it malfunctions, it can affect the fuel-air mixture, leading to a check engine light.
* Throttle Position Sensor (TPS): A malfunctioning TPS can disrupt the throttle signal, causing the engine to run poorly and trigger the light.
* Spark Plugs and Wires: Worn or damaged spark plugs and wires can cause misfires, leading to a check engine light.
* Fuel System Issues: A clogged fuel filter, bad fuel pump, or faulty fuel injectors can all contribute to the check engine light.
* Vacuum Leaks: A vacuum leak can disrupt the engine's airflow, causing it to run lean and triggering the light.
* Evaporative Emissions System (EVAP): Issues with the EVAP system, responsible for controlling fuel vapors, can also cause the check engine light.
* Catalyst Converter: A clogged or failing catalytic converter can affect exhaust flow and trigger the light.
Diagnosis:
* OBD Code Reader: The most reliable way to pinpoint the cause is to use an OBD code reader to retrieve diagnostic trouble codes (DTCs). These codes provide specific information about the issue.
* Visual Inspection: Check for obvious signs of wear and tear, such as loose connections, damaged wires, or leaks.
* Testing Individual Components: If the issue is not immediately apparent, you may need to test specific components like the O2 sensor, MAF sensor, or TPS using a multimeter.
Note:
* The 1991 Toyota truck with a 22RE does not have a standard OBD-II port. You might need a specific adapter for older vehicles.
* It's always recommended to consult a qualified mechanic for diagnosis and repair if you're not comfortable performing these tasks yourself.
Remember, it's essential to address the underlying cause of the check engine light to avoid further damage and ensure proper engine performance.
