What exactly is the check engine light for?
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Senior Member
Joined: Apr 2004
Posts: 218
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From: Maple Valley, WA
What exactly is the check engine light for?
I've had a few problems with my 1999 F-150 and the check engine light hasn't come on. Yesterday I threw a spark plug (3rd one back on drivers side) and no light. I'm wondering why the computer didn't pick up that the truck was only running on 7 cylinders.
I'm wondering what exactly the check engine light comes on for and what it doesn't.
I'm wondering what exactly the check engine light comes on for and what it doesn't.
Technical Article Contributor
Joined: Dec 1997
Posts: 9,417
Likes: 11
From: Windsor,Ontario,Canada
The SES light comes on to indicate a problem with an emissions compliant system failure. It also indicates Power train control malfunctions. DTC, Diagnostic Trouble Codes, are what the PCM stores in memory to help the technician to diagnose the problem. Hence the name. Not all DTCs will turn on the light. I am sure that if you scan for codes you will find one for the #6 cylinder.
Regards
Jean Marc Chartier
Regards
Jean Marc Chartier
Senior Member
Joined: Jan 2005
Posts: 130
Likes: 0
From: Dublin, OH
The whole OBD-II (standard that includes the check engine light) is mandated in the US by the California Air Resources Board (CARB) and the Environmental Protection Agency (EPA). The purpose of OBD is to ensure that the vehicle's emission controls are working and the vehicle is operating in such a way (no misfires, etc.) that emissions aren't too high. This is why it monitors for misfires (elevated HC's) and requires downstream O2 monitors (check catalyst efficiency) but doesn't monitor vital mechanical conditions like oil pressure or overheating.
There is some inadvertant overlap of emissions stuff and mechanical usefulness outside of emissions. The manufacturers have also added to the base OBD-II system beyond what is required by CARB/EPA for various reasons including servicability.
Some of the technology is pretty cool. Detecting knock with a piezoelectric crystal and automatically correcting for it before you hear it using spark timing, EGR, and enrichment is pretty cool. Detecting misfires and assigning them to a particular cylinder is pretty damn cool. But the OBD standard really doesn't care if your truck has mechanical problems, as long as the government emissions standards aren't endangered.
There is some inadvertant overlap of emissions stuff and mechanical usefulness outside of emissions. The manufacturers have also added to the base OBD-II system beyond what is required by CARB/EPA for various reasons including servicability.
Some of the technology is pretty cool. Detecting knock with a piezoelectric crystal and automatically correcting for it before you hear it using spark timing, EGR, and enrichment is pretty cool. Detecting misfires and assigning them to a particular cylinder is pretty damn cool. But the OBD standard really doesn't care if your truck has mechanical problems, as long as the government emissions standards aren't endangered.