P0306 on a Chevrolet Silverado 1500

What P0306 usually means on a Silverado 1500

P0306 isolates the misfire to cylinder 6, another of the AFM-deactivating cylinders on the 5.3L V8. When cylinder 6 misfires hard and the engine ticks, a collapsed AFM lifter is high on the list, more so than a coil or plug. On engines without AFM, or where there is no tick, the ordinary single-cylinder ignition and fuel suspects apply. Knowing that cylinder 6 is an AFM cylinder shapes the whole diagnostic approach on these trucks.

Most likely causes on this model

1. Collapsed AFM lifter on cylinder 6 (5.3L)

   Cylinder 6 deactivates under AFM, so a hard misfire there with a tick points to a failed lifter, a mechanical failure inside the engine.

2. Failed coil or worn plug on cylinder 6

   The routine single-cylinder misfire cause; swap-test the coil and inspect the plug before assuming anything internal.

3. Oil-fouled plug from AFM oil consumption

   An oil-consuming 5.3L can foul cylinder 6's plug, producing a misfire that recurs until the oil issue is dealt with.

4. Injector or compression fault on cylinder 6

   A leaking injector or low compression, possibly from a lifter-damaged cam lobe, causes a misfire ignition parts will not cure; a compression test confirms.

What it costs on a Silverado 1500

Ignition parts for cylinder 6 are inexpensive; an AFM lifter failure is a teardown-level, four-figure repair that should include a cam lobe inspection for that cylinder. As with the other AFM cylinders, the money-saving move is confirming lifter versus ignition before opening the engine.

Fixing it

Listen for a tick and check compression on cylinder 6 before buying parts. If ignition components are fine and the cylinder is an AFM cylinder with a tick, plan for lifter work and inspect the camshaft lobe.

For the full step-by-step diagnosis order (any vehicle), see the main P0306 guide.

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