Honda V6 VCM Misfire Spark Plugs & Fouled Cylinders

By the Radman Auto Repair team, independent auto repair in Etobicoke since 1999 · Updated November 2026

Honda’s 3.5-litre V6 uses Variable Cylinder Management (VCM) to shut off cylinders on the highway. Over time the cylinders that switch off can burn oil and foul their spark plugs, causing misfires, a shaking engine and a flashing check engine light.

Symptoms

What Causes It

Before You Start

• Park on level ground, set the parking brake and chock the wheels. Never work under a car held up only by a jack: use rated jack stands.
• Let the engine and exhaust cool before you touch them; coolant systems are under pressure when hot.
• Wear safety glasses and gloves, and disconnect the 12V battery before unplugging electrical parts or working near airbags.
• Check for open recalls on your VIN (Transport Canada or the manufacturer’s site) before you buy parts: a recall repair is free at the dealer.
• Remove the plugs only from a cold engine: aluminium cylinder heads strip easily when hot.

Step-by-Step: Honda V6 VCM Misfire

1. Scan the codes. Read the codes and freeze-frame data. Note which cylinders are misfiring.
2. Check the oil. Check the oil level and how much you add between changes. Heavy oil use points to the rings.
3. Get to the rear plugs. The front bank is easy. For the rear bank, remove the wiper arms and plastic cowl panel (10 mm nuts and clips).
4. Swap a coil. Move the coil from the misfiring cylinder to another one, clear the codes and drive. If the misfire moves, replace that coil.
5. Remove the plugs. Blow debris out of the plug wells first, then remove each plug. Wet black oil on the tip confirms oil fouling.
6. Install new plugs. Thread each new plug in by hand, then tighten to the torque in the service manual. Don’t use anti-seize unless the plug maker says to.
7. Refit the coils. Put a little dielectric grease in each coil boot, refit the coils and connectors, and refit the cowl and wipers.
8. Clear and test. Clear the codes and test-drive at highway speed. Recheck the plugs after a few thousand kilometres if oil use is high.

When to Stop and Bring It In

• The check engine light keeps flashing after new plugs: stop driving hard to protect the catalytic converter.
• The plugs foul again within a few thousand kilometres: the rings need attention, and a compression and leak-down test is next.
• A plug won’t come out easily or the threads feel rough.
• You need the engine mounts checked as well (see car shaking with check engine light).

Not sure, or out of time? Radman Auto Repair in Etobicoke does this repair every week. Book online or call (416) 742-4521.

Also Known As

Owners call this the “Honda VCM problem”, “Odyssey misfire at highway speed”, “Pilot oil-fouled spark plugs”, “Honda P0301 P0302 P0303” or “VCM piston ring problem”. VCM stands for Variable Cylinder Management.

Frequently Asked Questions

See also Honda Repair & Service, Spark Plug Replacement, P0300 Misfire Diagnosis, Flashing Check Engine Light.

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