The Active Fuel Management (AFM) system in GMC vehicles, designed to improve fuel efficiency by switching between four and eight cylinders, can sometimes cause issues and trigger OBD2 codes. Understanding how this system works and the common problems associated with it can help GMC owners diagnose and address these issues effectively.
One frequent complaint related to the GMC AFM system is engine vibration at specific speeds. This can manifest during acceleration and deceleration, often feeling like a noticeable shudder or shaking. While there can be multiple causes of vehicle vibration, a malfunctioning AFM system is a known contributor. In some cases, the transition between V4 (four-cylinder) and V8 (eight-cylinder) modes can be rough, leading to a perceptible vibration.
Another common problem associated with the GMC AFM system involves the fuel injectors. Because the system deactivates certain cylinders during V4 mode, the remaining active injectors are required to work harder. This increased workload can potentially lead to premature wear and tear or even injector failure. Faulty injectors can cause misfires, rough idling, reduced power, and decreased fuel efficiency, often triggering specific OBD2 codes.
Diagnosing AFM-related problems often requires the use of an OBD2 scanner. This device allows you to read diagnostic trouble codes (DTCs) stored in the vehicle’s computer. Specific codes related to the AFM system can pinpoint the source of the issue, such as a faulty actuator, sensor, or solenoid. Using an OBD2 scanner can save significant time and money by guiding you towards the correct repair. Furthermore, some aftermarket devices can modify the AFM system’s behavior, such as disabling V4 mode entirely.
While these devices can offer solutions to AFM-related issues, they can also introduce new challenges. For instance, some users have reported that these devices can occasionally “go to sleep” or malfunction after periods of inactivity, requiring a reset or reconnection to restore functionality. It’s crucial to research and choose reputable aftermarket devices and understand their potential limitations.
Ultimately, understanding how the GMC AFM system works, recognizing its common problems, and utilizing diagnostic tools like OBD2 scanners are essential for maintaining these vehicles. Addressing issues promptly can prevent further damage and ensure optimal performance and fuel efficiency.
