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Cylinder 8 is the last cylinder on the passenger bank of most V8 engines. Corvette LS3, Escalade 6.2L, and Dodge HEMI owners frequently encounter this code after 80k miles. The coil swap test takes 10 minutes and can save you hundreds in unnecessary parts. See top-rated scanners on Amazon ↗
🗺️ Where Is the Problem?
Blueprint view - P0308 fault localized to cylinder #8 (spark plug, ignition coil, or fuel injector)
These are statistical causes across ALL vehicles - your exact car may rank differently
For example, on a Honda 4-cyl the downstream O2 sensor causes P0308 64% of the time, but on a GM 5.3L V8 the catalytic converter is the cause 71% of the time. Get a probability ranking built specifically for your year, make, model, and mileage.
🔎 Get the ranking for my exact car - $5.99 →
🎯 Top Causes & Probability
50%
#1 - Most Likely
Bad Spark Plug (Cylinder 8)
A worn or fouled spark plug in cylinder 8 is the most common cause of P0308. On high-performance V8 engines like the Corvette LS3 and Escalade 6.2L, extended plug intervals under hard driving conditions accelerate electrode wear. Replace all 8 plugs when you service cylinder 8.
🔩 Part
$5–$30
👨🔧 Labor
$0–$80
⚡ DIY Difficulty
Easy–Med
30%
#2 - Check First
Failed Ignition Coil (Cylinder 8)
The coil-on-plug unit for cylinder 8 has failed. On performance V8 engines, coils can fail due to heat stress, especially when the spark plugs are worn and require higher voltage. The coil swap test is the quickest and cheapest way to confirm.
🔩 Part
$20–$120
👨🔧 Labor
$30–$100
⚡ DIY Difficulty
Easy
12%
#3 - Less Common
Clogged Injector (Cylinder 8)
A restricted fuel injector on cylinder 8 creates a lean misfire. High-performance engines are particularly sensitive to injector flow imbalances. Injector flow testing can confirm whether cylinder 8's injector is delivering the correct amount of fuel compared to others.
🔩 Part
$25–$150
👨🔧 Labor
$50–$100
⚡ DIY Difficulty
Medium
8%
#4 -
Low Compression (Cylinder 8)
Low compression in cylinder 8 from a burned valve, worn rings, or damaged head gasket results in a persistent misfire. On high-mileage performance engines, cylinder 8 (last in the passenger bank) can develop issues from heat accumulation and hard use cycles.
🔩 Part
$100–$2,000+
👨🔧 Labor
$500–$3,000
⚡ DIY Difficulty
Hard
🚗 Most Affected Vehicles
🔧 Step-by-Step Diagnosis
- Swap Spark Plug Cylinder 8 → Cylinder 7 - Move the cylinder 8 plug to cylinder 7. Install a known-good plug in cylinder 8. Clear codes and test drive. If P0307 now appears instead of P0308, the plug is faulty - replace all 8 plugs.
- Swap Ignition Coil Cylinder 8 → Cylinder 7 - If the plug didn't change the code, swap the coil to cylinder 7 and retest. A code that migrates to cylinder 7 confirms the coil is failed. Inspect the coil boot for carbon marks before replacing.
📍 Find a Trusted Shop Near You
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Tips for Choosing a Shop
- Ask if they charge a diagnostic fee and whether it applies toward the repair
- Request a written estimate before approving any work
- Ask specifically about the part brand - OEM vs. aftermarket matters for this code
- Check Google reviews for recent mentions of the specific repair you need