Originally posted by Bob Blaylock:
A steady CEL usually means something fairly harmless; if there are no other symptoms, then you're probably just polluting more than you should, and perhaps burning more gas than you should.
You can't really generalize a steady CEL light as 'no big deal'. There are about 100 different possible error codes that can trigger a steady check engine light. Some are no big deal, others a major deal, or might start out as no big deal but turns into a bigger deal as you drive. For example, the first time my cat were defective, my CEL came on steady, yet it ran OK for about 500 miles. I ignored it, until suddenly the engine started losing power big time, and knocking like crazy under acceleration. Then I brought it into the dealer, and it was diagnosed with plugged and disintegrated cat converters. I was lucky in that my engine was OK, but I have heard of several stories with these defective cats causing complete engine failure due to sucking disintegrated cat material into the engine through the EGR and ruining the cylinder walls. All the while the CEL is on steady. That's just one example - there are many others.
Bottom line is don't ignore any check engine light that stays on, whether its steady or blinking. Ignoring it can do a lot more than just pollute - it can ruin your engine. You should know what the code is before deciding to ignore it.
