: emissions light comes on

03-17-08, 12:22 AM
I am looking at a 1996 cadi eldorado 300 hp why did the check engine light or the ckeck emissions light come on. we found the filler cap for the engine oil off. we replaced the oil cap and the light went out after a few miles.

03-17-08, 07:15 AM
This will happen on most anything that uses a Mass Air Flow sensor.

The crankcase ventilation system (PCV) uses filtered air from the induction system to vent into the crankcase as the PCV valve or orifice remove blowby gases from the engine. This air is "metered" and it is taken into account when the air fuel calculations are made. If you open the oil filler, unmetered air can enter the crankcase and the air fuel calculations will be off. Essentially it is a vacuum leak.

The MIL or "Malfunction Indicator Lamp", which used to be referred as the CEL or Check Engine Lamp, comes on whenever the computer calculates that the EPA regulated emissions are being exceeded by 1.5 times.
Once the cap was put back on, the air/fuel ratio returned to normal and the self tests ran to let the computer know. Once the tests passed a given number of times in a given time period the light was turned back off.

03-17-08, 09:48 AM
Poll for what? The two choices are not relevant to the question, and eWill3 has answered the question so what's the point?