how to diagnose a check engine light on GMC Sierra T1XX (2019-Present)

Learn how to diagnose and fix the check engine light issue on GMC Sierra T1XX (2019-Present). Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

• Tools Required: OBD-II scanner, socket set, multimeter, torque wrench, vacuum gauge.
• Disconnect the vehicle's battery to prevent electrical shorts.
• Allow the engine to cool if it has been running to avoid burns.

2. Code Clearing and Component Inspection

1. Connect the OBD-II scanner to the vehicle's diagnostic port.
2. Retrieve and document any stored error codes.
3. Clear the codes and observe if they return after a short test drive.
4. Visually inspect engine components such as the air filter, fuel lines, and exhaust for any signs of damage or wear.

3. Addressing Specific Codes

1. Based on the retrieved DTCs, address each issue:
   • For P0171/P0174 (lean condition), check fuel injectors and fuel pressure.
   • For P0300 (random misfire), inspect ignition components and fuel quality.
   • For P0420 (catalytic converter efficiency), check for exhaust leaks and test the O2 sensors.
2. Replace any faulty components identified during inspections (e.g., spark plugs, fuel injectors).

4. Reassembly and Testing

1. Reassemble any components removed during the inspection.
2. Reconnect the battery and ensure all connections are secure.
3. Start the engine and let it idle to ensure no CEL is illuminated.