P0305 on Chevrolet: How to Diagnose & Fix
Cylinder 5 Misfire Detected
4 Chevrolet models · 4 documented issues · 3 critical · $100-$7,500 repair
P0305 on Chevrolet by model: symptoms, diagnosis and fix
Vans built with the 6.0L L96/LC8 Vortec V8 (the volume engine in Express 2500/3500 from 2010 on) can break a rocker arm, producing an engine tick and a hard misfire on one cylinder. GM addressed it in preliminary information bulletin PIP5522B, which specifically lists 2017-2018 Chevrolet Express among the affected vehicles and warns that a broken rocker arm can let the valve drop into the cylinder and cause catastrophic engine failure. The Express 4.8L L20 and 6.0L L96 do not use Active Fuel Management, so the AFM collapsing-lifter story that plagues Silverado/Tahoe 5.3L and 6.2L engines does not apply to these vans - this is a rocker/valvetrain hardware failure, not an AFM lifter failure. Owners typically hear a distinct top-end tick that does not go away as the engine warms, followed by a stored misfire code.
Common Symptoms
- Persistent top-end ticking that does not quiet as the engine warms
- Single-cylinder misfire
- Rough idle
- Check engine light with random or cylinder-specific misfire codes
- Loss of power
- Loud clatter followed by catastrophic noise if the valve drops
How to Fix
Diagnose the ticking cylinder with a cylinder-balance test and stored misfire data, then pull the valve cover on the affected bank and inspect the rocker arms and pushrods before assuming a lifter problem. If a rocker is broken and the valve has not dropped, reinstall any dislodged valve keepers and replace all 8 intake rocker arms per PIP5522; inspect the valve, seat and piston crown for contact damage - a dropped valve means a head or short-block replacement. Catch it early: continuing to drive on a broken rocker is what turns a few-hundred-dollar rocker job into an engine. There is no recall or free remedy; PIP5522B is a service bulletin, not a warranty extension, so coverage depends on remaining powertrain warranty.
Sources for this issue (3)
- GM PIP5522D - 6.0L Engine Noise and/or Misfire (broken rocker arm), 2017-2018 Express/Savana L96 LC8tsb
- GM Issues Service Bulletin PIP5752A for Faulty V8 Engine Valve Springs (springs used across the lineup including the Chevy Express van)tsb
- P0300 on 2014-2018 Chevrolet Express: Random Misfire Causes and Fixesarticle
A well-documented problem on the Atlas inline-five engines is worn or leaking intake valves and valve seats in the cylinder head, concentrated on 2004-2006 trucks, for which GM issued service bulletins and special coverage. Owners report sudden misfires, rough running, low compression, flashing MIL, and in some cases complete loss of power. This issue appears in owner forums, repair discussions, and NHTSA complaints, and typically requires cylinder head replacement or machine work rather than simple ignition parts.
Common Symptoms
- rough idle
- flashing check engine light
- cylinder-specific misfire
- low compression on one cylinder
- hard starting
- loss of power
- engine shaking under load
How to Fix
Diagnosis usually starts with misfire codes, compression/leakdown testing, and borescope inspection if one cylinder shows very low compression. If an intake valve or valve seat is leaking or worn, the durable repair is removing the head and replacing it with an updated/remanufactured unit or having a reputable machine shop rebuild it. Ignition coils and plugs should only be replaced after confirming the misfire is not mechanical.
Sources for this issue (4)
- GMC Canyon Years To Avoid - intake-valve-seat wear on 2004-2006 2.8L/3.5L, GM special coverage 07123Aarticle
- NHTSA owner complaints - 2005 Chevrolet Colorado (intake valve / cylinder head misfire reports)nhtsa
- NHTSA owner complaints - 2006 Chevrolet Colorado (valve seat / cylinder head misfire reports)nhtsa
- 3.7 i5 dropping valves? | ColoradoFansforum
The fuel injector wiring harness on the Duramax diesel routes across the top of the engine under the valve covers. The harness rubs against the valve cover and rocker arms, causing the insulation to wear through and the wires to short or open. When an injector wire is damaged, the affected cylinder misfires, the engine runs rough, and white smoke pours from the exhaust. The chafing is accelerated by engine vibration and can affect multiple cylinders over time. GM released updated harness routing clips but the fundamental design has the harness in a high-wear location.
Common Symptoms
- Engine misfires on one or more cylinders
- White smoke from exhaust
- Rough idle that develops gradually
- Check engine light with injector circuit codes
- Engine runs on fewer than 8 cylinders
- Intermittent misfires that come and go
How to Fix
Remove the valve covers and inspect the injector harness for chafing (requires 2-3 hours labor). Damaged sections can be repaired with heat-shrink tubing and solder ($100-$300 for repair). If the harness is severely damaged in multiple places, a complete replacement harness costs $200-$500 and takes 3-5 hours to install. Add additional harness routing clips and protective loom to prevent recurrence. Some diesel specialists reroute the harness outside the valve cover (external harness conversion) to eliminate the chafing issue permanently.
Sources for this issue (1)
The Active Fuel Management (AFM) and Dynamic Fuel Management (DFM) systems on the 5.3L and 6.2L V8 engines deactivate cylinders to save fuel by collapsing hydraulic valve lifters. These lifters have a complex locking pin mechanism that fails, causing the lifter to collapse and the affected cylinder to misfire. A collapsed lifter can also damage the camshaft lobe it rides on, turning a $300 lifter into a $3,000 camshaft and lifter replacement. The issue affects 2007+ Suburbans and is one of the most complained-about GM V8 problems. The Suburban switched from AFM to DFM with the 2021 redesign (5.3L L84, 6.2L L87), but lifter failures continue.
Common Symptoms
- Engine misfire on one or more cylinders
- Ticking or tapping noise from engine
- Check engine light with misfire codes
- Rough idle
- Reduced engine power
- P0300 random misfire or specific cylinder misfire code
How to Fix
Replace the failed lifter(s) and inspect the camshaft for damage. A single-side lifter replacement (one bank of 8 lifters) costs $1,500-$2,500 including labor. If the camshaft is damaged, add $500-$1,000 for a new cam and installation. Many owners opt to replace all 16 lifters and delete the AFM/DFM system with an AFM delete kit ($200-$400) and a custom tune that disables cylinder deactivation. This eliminates the root cause but requires a tuner ($400-$600). An aftermarket Range Technology AFM/DFM disabler (about $300) is a plug-in alternative that keeps all cylinders active without a tune.
Sources for this issue (2)
P0305 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0305 mean on a Chevrolet?
P0305 stands for "Cylinder 5 Misfire Detected." This code means the engine control module detected a misfire on cylinder number 5, meaning that cylinder is not burning its air-fuel mixture properly on some combustion cycles. The computer senses misfires by watching for tiny fluctuations in crankshaft speed each time a cylinder fails to fire correctly. A misfire wastes fuel, can make the engine run rough or shake, and dumps unburned fuel into the exhaust, which can overheat and damage the catalytic converter. It generally points to a problem with spark, fuel delivery, or compression specifically affecting cylinder 5. On Chevrolet it is documented across 4 models: Express, Colorado, Silverado 2500HD, Suburban.
What are the most common causes of P0305?
The most common causes of P0305 are: Worn or fouled spark plug on cylinder 5, Failed ignition coil or coil pack for cylinder 5, Faulty or clogged fuel injector on cylinder 5, Vacuum or intake air leak affecting that cylinder, Bad spark plug wire or boot (on applicable engines), Low compression from worn rings, valves, or head gasket, Carbon buildup or sticking valve on cylinder 5, Lean or rich fuel condition affecting the cylinder. The specific cause varies by vehicle.
How much does it cost to fix P0305 on a Chevrolet?
Published repair estimates on Chevrolet range from $100 to $7,500 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.