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What is the significance of a flashing CEL, vs. a steady one?

I recently read and cleared the codes on my 1996 Lincoln Mark VIII. After driving it for awhile, the CEL came back on. During that trip, it remained on and steady the entire time. In the next trip, the car started with the CEL on solid. A bit of a way down the road though, the CEL began to flash. It would flash for awhile, then be steady for awhile. There seemed to be no real consistency with the duration of either behavior.

When I'd pulled the codes, here's what I'd found:

P1537 - Intake Manifold Runner Stuck Open, Bank 1
P0304 - Misfire, Cylinder 4
P0174 - System Too Lean, Bank 2

So, what would be causing the CEL to flash occasionally, as opposed to just staying steady? Is this behavior something unique between makes and models, or is it generally standard across all OBD II systems?

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A flashing check engine light means you may be doing damage to the catalytic converter if you continue to drive the vehicle. If the misfire is bad enough too much raw fuel is going into the exhaust, enough to do damage to the converter.

I'm not sure it's required on OBD II, but several manufactures flash the light for this reason.

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