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My Toyota Matrix is slightly overdue for the precautionary replacement of the serpentine belt. The belt produced not the slightest noise, and so I continued to use it.

Today the temperature dropped from morning to night from 40F to 15F. The CEL flashed when I heated the engine for the evening.

I needed to drive urgently for 15 minutes, and so I took the risk of not parking despite the flashing CEL. The flashing stopped halfway through the ride. When I stopped, the code reader showed a complete set of all four cylinders misfiring: P0300, P0301, P0302, P0303, P0304.

Can the aged serpentine be a little dry and hence providing too little grip? Is a serpentine slip a probable cause for all four cylinders to misfire at once?

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  • Even though the light is flashing did the vehicle feel like it was misfiring?
    – vini_i
    Commented Jan 5, 2017 at 2:05
  • The power was intact. The engine sound was normal. The vibration in the car was normal. I was worried that some section of the coolant had frozen (I hadn't powered the block heater), and so I shifted a bit earlier than usual to avoid overheating the engine (its temperature was normal).
    – Calaf
    Commented Jan 5, 2017 at 2:10
  • Frozen coolant would cause a severe misfire if it cracked the block but then the engine would have terrible power loss. A slipping belt could cause the computer to think it is misfiring without there actually being a misfire. This is a rare case scenario. Usually the belt is screaming like a banshee first.
    – vini_i
    Commented Jan 5, 2017 at 2:16
  • lol @ banshee! It was warm and humid for several days and the car doors were frozen shut after accumulating little droplets. They needed quite a tug. Could water have condensed in the air intake filter, then frozen suddenly? The mixture would then be exceptionally rich. Might that trigger all-engine misfire?
    – Calaf
    Commented Jan 5, 2017 at 2:22
  • That would also cause severe loss of power.
    – vini_i
    Commented Jan 5, 2017 at 2:25

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To answer your question directly: To my knowledge there is no way a slipping serpentine belt would cause a single cylinder misfire, let alone all of them to show a misfire. The serpentine belt and ignition systems are two completely different systems.

The only commonality between the two is the charging system (alternator), but even so, as @vini_i stated, you'd have heard the screaming of the belt if there was an issue with that portion of it (plus all kinds of dash lights going off, besides the CEL). The ignition system can run off of battery power alone without issue for a relatively long time before you'd start seeing misfires occur.

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  • I see. I must be confusing ignition system timing with valve timing. I understand that replacing the serpentine belt is a delicate job because it must be positioned such that the valves do not get smashed by an incorrect positioning of the serpentine. But you're saying that that issue is altogether separate from ignition timing, which is where the codes are pointing.
    – Calaf
    Commented Jan 5, 2017 at 2:51
  • @Calaf - You are confusing the two ... the serpentine belt is the belt which runs the alternator, AC compressor, and power steering pump. The timing belt is what you are talking about. Still, if it slips, the engine will quit running altogether, not just get some misfire codes.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Jan 5, 2017 at 3:01
  • @Calaf - PS: The timing belt won't give you any noise before it goes ... If it slips or self destructs, it just happens. You'll know it when it does, because the engine will die. If you are due for a timing belt replacement, don't hesitate to do it. A couple hundred now to get it replaced, or a couple thousand (or more) later to replace the entire engine ... it's that important.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Jan 5, 2017 at 3:03
  • Ah.. So the only thing delicate about the serpentine belt is its tension. If it does snap, the battery no longer charges, etc.. but no permanent damage occurs in the engine or the car. About the timing belt.. I think mine is a metal chain (sort of like a bike chain) that is buried inside the front of the engine. The car owner's manual doesn't say a word about even inspecting the timing belt. Only the "Engine Accessory Drive Belt" is discussed.
    – Calaf
    Commented Jan 5, 2017 at 3:22
  • @Calaf - If it is a chain (double check to make sure), then you should be golden. Most chains are supposed to be "for the life of the car" (though some of them fall way short of this goal). And you are quite accurate on the serpentine belt that no real damage will occur if one should fail, but you should still try to get them changed regularly because they don't usually fail spectacularly, but rather wear out over time and start slipping and causing other minor issues which can be hard to figure out and point back to the belt.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Jan 5, 2017 at 3:27

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