2003 gmc Yukon check engine light comes on what could be the problem?

A check engine light on a 2003 GMC Yukon could indicate a wide variety of problems. It's impossible to diagnose the specific issue without more information. The light itself only tells you that the onboard diagnostic system (OBD-II) has detected a problem.

To figure out what's wrong, you need to:

1. Get the Diagnostic Trouble Codes (DTCs): This is the most crucial step. You can do this in a couple of ways:

* OBD-II Scanner: The cheapest and easiest method is to buy a relatively inexpensive OBD-II scanner from an auto parts store. Plug it into the OBD-II port (usually under the dashboard) and it will read the codes. The codes are numbers (e.g., P0171, P0420).

* Auto Parts Store: Most auto parts stores will scan your vehicle for free. They can tell you the code(s) and sometimes even give you a potential diagnosis.

2. Research the DTCs: Once you have the code(s), search online (e.g., Google the code) or consult a repair manual for your specific year and model of Yukon. This will give you a much better idea of the potential problem. Common issues for that year include:

* Oxygen Sensor Issues: These are fairly common and can trigger the check engine light.

* Mass Airflow Sensor (MAF) Problems: This sensor measures the amount of air entering the engine. A faulty MAF can lead to poor performance and the check engine light.

* Catalytic Converter Issues: A failing catalytic converter can cause the check engine light to illuminate. This is often expensive to repair.

* Ignition System Problems: Issues with spark plugs, ignition coils, or other ignition components can trigger the light.

* Evaporative Emission System (EVAP) Leaks: Leaks in the fuel system can cause this.

* Transmission Issues: While less common, transmission problems can also trigger the light.

3. Consider the Symptoms: Along with the check engine light, are you experiencing any other symptoms? Does the engine run rough, is there reduced power, is the gas mileage poor, is there unusual smoke from the exhaust? These symptoms can help narrow down the possibilities.

Without the DTCs, any guess I make would be purely speculative and potentially misleading. Getting the codes is the only reliable way to start troubleshooting the problem. Don't ignore the check engine light; driving with a malfunctioning system can cause further damage.