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What P0304 means for your Chevy Silverado
Your Silverado's ECM detected that cylinder 4 isn't firing properly - the crankshaft position sensor saw the rotational speed dip slightly each time cylinder 4 was supposed to combust. On the 5.3L Silverado, P0304 is famously an AFM (Active Fuel Management) lifter collapse - cyl 4 is one of the four AFM-deactivated cylinders and the most common to fail.
🎯 Top Causes on the Chevy Silverado
60%
#1 CAUSE
AFM Collapsed Lifter on Cyl 4
Cyl 4 is one of the four AFM-deactivated cylinders on the 5.3L V8 (firing order 1-8-7-2-6-5-4-3; AFM deactivates 1, 7, 4, 6). When the AFM lifter on cyl-4 fails to re-activate or collapses entirely, you get a steady P0304 with a sewing-machine tick from the top of the engine. The collapsed lifter eventually scores the cam lobe, spreading damage. This is the single most common 5.3L L83 problem and the basis for the 2024 class-action settlement (Siqueiros v. GM). Fix is lifter replacement + cam replacement if scored + AFM-delete tune.
Lifter Set
$180-$400
Cam + Lifters
$500-$900
Shop Repair
$1800-$3500
25%
#2 CAUSE
Cyl 4 Ignition Coil
GM individual COP coils on the L83 and L86 (ACDelco D510C / 12619161). Coils fail between 90k-150k miles. Cyl 4 is on the driver-side rear, easy to access. Swap test with cyl-2 confirms. Aftermarket NGK U5023 is a reliable option. Use AC Delco 41-985 iridium plugs gapped to 0.040".
OEM Coil
$60-$110
Aftermarket
$40-$70
w/Labor
$120-$240
15%
#3 CAUSE
AFM Solenoid Sticking
AFM uses oil-pressure-activated solenoids mounted in the valley pan under the intake. A clogged or stuck cyl-4 AFM solenoid causes the lifter to hang in the wrong state - sometimes deactivated when it should be active, leading to misfires under load. Symptom: misfire goes away on heavy throttle. Replace the solenoid (intake comes off, 3-4 hour job) plus an AFM delete tune to prevent recurrence.
AFM Solenoid
$80-$140
Valley Cover Gasket
$25-$50
w/Labor
$400-$700
🚗 Most Affected Silverado Model Years
| Year | Engine | Primary Cause | Typical Mileage | Notes |
|---|---|---|---|---|
| 2007-2014 | 5.3L LMG (Gen IV AFM) | AFM lifter cyl-4 | 80k-140k | Most reported failure |
| 2014-2019 | 5.3L L83 (Gen V DI AFM) | AFM lifter | 60k-120k | Class-action settlement covers many VINs |
| 2019-2020 | 5.3L L84 (DFM) | Lifter / coil | 40k-90k | Newer Dynamic Fuel Mgmt |
| 2014-2020 | 6.2L L86/L87 | AFM lifter | 80k-140k | Same architecture |
🔧 How to Diagnose P0304 on a Chevy Silverado
- Listen for a sewing-machine tick at the top of the engine. Use a long screwdriver as a stethoscope on each valve cover. The bad lifter side will tick distinctly. P0304 + tick = lifter, almost guaranteed.
- Swap the cyl-4 coil with another cylinder and clear code. If misfire moves with the coil = ignition. If it stays = lifter.
- Check AFM status with a scanner (BlueDriver, OBDLink MX+, or GM Tech 2). AFM should activate above 1000 rpm in light cruise. If AFM is stuck on or stuck off on cyl 4, suspect the solenoid (not lifter).
Want a step-by-step walkthrough specific to your Chevy Silverado? Run a $5.99 AI diagnosis report - we narrow the cause to your year, engine, and symptoms.
❓ Frequently Asked Questions
Is my Silverado covered by the AFM lifter class-action settlement?
The 2024 Siqueiros v. GM settlement covers 2014-2019 Chevy Silverado / GMC Sierra with 5.3L L83 or 6.2L L86 engines for lifter and AFM-related repairs. Reimbursement typically runs $5,500-$8,000 for documented repairs. Check your VIN at the official settlement site.
Should I do an AFM delete on my Silverado?
If you're replacing lifters because of failure, absolutely yes - add the AFM-delete tune ($300-$500) and solenoid blockers ($100) while you're in there. Otherwise the new lifters fail again in 50k-80k miles. If your truck is under 80k miles and trouble-free, a $170 Range Technology AFM disabler is a cheap preventive measure.
How do I know if my Silverado lifter is collapsed?
Three signs: (1) sewing-machine tick at the top of the engine that doesn't go away when warm, (2) steady single-cylinder misfire that doesn't move with coil swap, (3) misfire that comes back under cruise (when AFM tries to deactivate). All three = collapsed lifter.
How much does Silverado lifter replacement cost?
DIY: $250-$500 in parts (full lifter set, intake gaskets, RTV, recommended cam + AFM delete kit pushes it to $700-$1000) and 8-12 hours. Shop: $1800-$3500 (or up to $4500 with cam replacement). Worth it to add AFM-delete tune ($300-$500) so you don't do this again.
Which cylinder is cylinder 4 on a Silverado V8?
GM small-block V8s: cyls 1-3-5-7 on driver side, 2-4-6-8 on passenger side. Cyl 4 is the second from the front on the passenger side - reasonably easy to reach.
See all P0304 causes (all vehicles) → · Related: Chevy 5.3L AFM Lifter Failure →