Active Fuel Management Misfire Codes Setting on HFV6 Gen2 Engines

Misfire DTCs P0300 (Engine Misfire Detected), P0302 (Cylinder 2 Misfire Detected) or P0305 (Cylinder 5 Misfire Detected) may be set on some 2016-2019 ATS; 2016-2020 CT6; 2016-2021 Camaro; 2017-2019 LaCrosse; 2017-2021 XT5, Colorado, Acadia, Canyon; 2018-2020 Regal; 2019-2021 Blazer; 2020-2021 CT5, and XT6 models equipped with the 3.6L engine (RPO LGX, LGZ) or 3.0L engine (RPO LGY, LGW).

Cylinder 2 and 5 are the Active Fuel Management (AFM) cylinders. Oil may be leaking past the AFM oil control valve solenoid, located in the camshaft cover, allowing inadequate oil pressure to the AFM solenoid and, in turn, deactivating the cylinder due to oil bleed off.

If there are not any signs of any ignition or fuel injection concerns, check the AFM solenoid on either cylinder 2 or 5, depending on which DTC is set. Remove and inspect the AFM solenoid and O-rings for any damage and inspect the bore inside the camshaft cover for abnormalities or porosity.

During service, the AFM solenoid may come out of the cover with the end broken off, which does not allow the new solenoid to be installed completely in the camshaft cover. (Fig. 4) Compare a new solenoid with the current solenoid to ensure the solenoid is still intact. Be sure to check the cover for any broken components where the bottom may have been pulled apart.


Fig. 4


Inside the camshaft cover with the solenoid removed, look for the end of the solenoid stuck in the bore. Compared with a clean bore (Fig. 5, A), a solenoid stuck in the bore (Fig. 5, B) will be easy to see and can usually be removed using a pick tool or a pair of transmission snap ring pliers. The solenoid will only be held in the bore with the O-ring.


Fig. 5


If the solenoid is the not the cause of the misfire, continue with the appropriate Service Information diagnostics.

For additional information, refer to Bulletin #21-NA- 036.


– Thanks to Bryan Salisbury

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One Comment

  1. joe bucci says:

    i had one of these and the deactivation lifter was bad. had no compression in cyl. 2. in order to get the valve cover off you have to remove the washer tub. you can then get the intake off. and finally the valve cover and intake manifold. while clear flooding the engine have a helper crank the engine. while your assistant is cranking look through the intake port to see if the valve are moving. if they are not moving replace all 4 lifters and rockers in the cylinder 2. note, special tool are required. follow the instruction step by step to install the tool. the tool does work verry good.

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