Experiencing unusual vibrations in your GMC truck? You’re not alone. Many GMC owners have encountered perplexing vibration issues, and sometimes, the culprit lies within the Active Fuel Management (AFM) system. This story, shared by a seasoned gearhead, highlights the potential connection between AFM, OBD2 diagnostics, and those frustrating vehicle vibrations.
The author recounts their experience with a 2007 GMC truck plagued by vibrations at specific speeds during acceleration and deceleration. Initial diagnoses pointed towards common culprits like the rear end and driveshaft, but thorough personal inspection ruled these out. Even a transmission check came back clean. Frustration mounted as the dealership’s initial assessment proved incorrect.
Alt text: Mechanic inspecting the driveshaft of a GMC truck for potential vibration causes.
Ultimately, the issue was traced back to the AFM system and fuel injectors. The AFM system, designed to improve fuel economy by switching between 4 and 8 cylinders, was suspected of causing engine imbalance and subsequent vibrations. This revelation came with a hefty $4,000 repair estimate, prompting the owner to trade in the truck for a newer 2015 Silverado.
This experience underscores a concern voiced by some experts: that GM’s AFM system, while intended to enhance fuel efficiency, may inadvertently lead to engine problems due to the inherent stress of switching cylinder modes. To combat this in their new Silverado, the owner opted for a Range Technologies AFM disabler. This device plugs into the OBD2 port and keeps the engine running in 8-cylinder mode continuously, effectively deactivating AFM. Interestingly, the owner reported improved fuel mileage after installing the disabler.
Alt text: Close-up of an OBD2 port in a vehicle with a diagnostic scanner connected.
However, a new issue arose with the Range Technologies unit. After periods of inactivity, the device seemed to “go to sleep,” allowing the AFM system to re-engage V4 mode until the unit was unplugged and re-plugged. This prompted the author to reach out to the community, asking if others have encountered similar problems with Range Technologies AFM disablers or comparable OBD2 devices designed to manage the AFM system.
Alt text: Range Technologies Active Fuel Management Disabler module, a common OBD2 device.
This personal account serves as a valuable lesson for GMC and Chevrolet truck owners dealing with unexplained vibrations. While OBD2 scanners can help diagnose a range of issues, understanding the potential role of the AFM system and considering AFM disablers as a solution (or being aware of their potential quirks) could be crucial in resolving these automotive puzzles. Further community input and expert opinions are valuable in understanding the long-term reliability and effectiveness of AFM disabler solutions.
