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My 2016 Honda Odyssey EX-L has fewer than 80k miles on it. Yet it's already had its check engine lights come on leading to replacing a few of the spark plugs and ignition coils. The problem hasn't recurred for a year, but I moved and now have the CEL coming back on. The shop I took it to now said to replace the #2 spark plug and coil, which was just replaced a year ago. The also suggested they could just replace all the spark plugs while they're at it. What could be causing this? I worry that if we don't really know why, I'll be back here again soon.

Edit: I came across some information on another forum about the Variable Cylinder Management (VCM) system in this vehicle being problematic and its recommendation of replacing the sparkplugs and then installing a VCM muzzler. I can't say I understood everything explained there, but it does sound pretty relevant to this situation. I'd be interested in any reactions/experiences with this solution.

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  • Welcome to Motor Vehicle Maintenance & Repair!
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Jun 2 at 0:15
  • Is one or more plug visually observed to be fouled upon removing and inspecting it, or is someone stating that it is fouled based on the CEL and diagnostic trouble codes?
    – MTA
    Jun 2 at 1:10
  • Anecdotally; my Odyssey's plugs got fouled when I ran the gas tank down to fumes. On Thursday I realized I was below empty while miles from any gas station, and on Friday the car lit up with the blinking CEL and I had it towed to the dealer. They replaced all the plugs and it went back to normal.
    – gowenfawr
    Jun 2 at 14:05

2 Answers 2

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A fouled spark plug is a sign of further issues. It can be caused by a number of things. A mechanic would need to visually inspect the spark plug and run further diagnostics to determine and confirm the cause of fouling. Fouled spark plugs are most commonly caused by incorrect air-fuel mixture or excessive oil in the combustion chamber.

Its very likely the ignition coil is fine. However, there is a good chance the ignition coil your old mechanic installed is not a factory replacement from Honda. Sometimes, aftermarket parts bought at your local parts store can be defective or fail prematurely.

I suggest you pull the number 2 spark plug and compare it to this chart from Champion Spark Plugs. This will help you determine what is causing your fouled plug.

Also, for your future reference, always replace ignition coils as a set and use the same brand for all 6. Different brand ignition coils produce different sinewaves and have different primary resistances.

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What are the codes for the CEL lights? You mentioned you moved. Do you live in a colder climate and have your driving habits changed to short, local trips that don't include highway driving?

When the coils & plugs were replaced last year, were they all replaced or just a few? If only a few, the others are likely in need of replacement.

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