Changes to the AFM and DFM Feature on 2021 Silverado 1500 and Sierra 1500

Some 2021 Silverado 1500 and Sierra 1500 trucks equipped with the 5.3L V8 engine (RPO L82) and 6L80 6-speed automatic transmission (RPO MYC) or the 5.3L V8 engine (RPO L84) (Fig. 19) and 8L90 8-speed automatic transmission (RPO MQE) may not have the Active Fuel Management/AFM (L82 engine) or Dynamic Fuel Management/DFM (L84 engine) feature. Beginning in March 2021, trucks produced without AFM or DFM are identified with RPO YK9 – Not Equipped with Cylinder Deactivation.


Fig. 19


TIP: Any truck with RPO YK9 cannot be reprogramed and changed to turn on or activate the AFM/DFM functionality.

AFM can provide maximum fuel economy under light load driving conditions by deactivating engine cylinders 1, 7, 6, and 4, switching to a V4 mode.

DFM has the ability to deactivate any combination of cylinder valves, which allows for a large variety of firing sequences. The control of every cylinder event optimizes engine performance so that peak efficiency is obtained throughout the range of engine operation.

While diagnosing engine or electrical wiring concerns on these models, keep in mind that internal components related to AFM or DFM functions will be present in the engines as well as related wiring, connectors and fuses. The Engine Control Module (ECM) will not be capable of activating the cylinder deactivation technology.

When diagnosing and repairing concerns regarding engine or electrical functions that may be related to AFM- or DFM-related hardware, follow the diagnostics in the appropriate Service Information. No changes have been made to AFM- or DFM-related components.

For additional information, refer to #21-NA-078.


– Thanks to Richard Renshaw

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