Here's what you should do:
1. Diagnose the problem: The best way to find out *why* the check engine light is on is to use an OBD-II scanner. These are relatively inexpensive and available at most auto parts stores. The scanner will read the diagnostic trouble codes (DTCs), which give you a specific indication of the problem. You can then look up the code online (many websites provide free DTC lookup services) or consult a repair manual.
2. Repair the problem: Once you know the DTC(s), you can address the root cause. This might involve:
* Replacing a faulty sensor (oxygen sensor, mass airflow sensor, etc.)
* Fixing a leak in the exhaust system
* Replacing a worn-out spark plug or ignition coil
* Addressing a problem with the catalytic converter
* Fixing a vacuum leak
* And many other possibilities depending on the code(s)
3. Clear the code (after repair): *Only after you've fixed the problem* should you clear the code. Many OBD-II scanners have a "clear codes" function. Some advanced scanners even allow you to erase specific codes. You can also often find this feature in many smartphone apps that work with OBD-II adapters.
Important Considerations:
* Don't just disconnect the battery: While disconnecting the battery for a short period might temporarily clear the light, it won't solve the underlying problem. The light will likely return.
* Professional help: If you're not comfortable diagnosing and repairing the problem yourself, take your Sierra to a qualified mechanic. They have the tools and expertise to properly diagnose and fix the issue. Attempting repairs without proper knowledge could cause further damage or injury.
In short, resetting the check engine light is the *last* step, not the first. Focus on finding and fixing the problem causing the light to illuminate.
