What does Evaporative Emission System Flow During Non-Purge (GM) mean and how do you fix it?
Thanks,Michael

 

The ECM has detected a drop in the fuel tank pressure when it's not suppose to drop. This is an emission related code; and maybe covered under warranty.

It does this (checks for purge at the wrong time) by commanding shut the valve that purges fumes from the fuel tank /charcoal canister that stores the fumes; while the engine is running. At the same time it commands open the valve that allows air into the fuel tank. While all this is taking place the pressure in the fuel tank is measured and compared to calibrated values; if not OK a DTC sets and if there are 2 consecutive trips when the DTC runs and fails the MIL (Malfunction Indicator Lamp) will turn ON.

You probably won't notice any driveability problems, but since this is an emission related DTC it may increase your car's pollutant output.

Hope this helps.

These EVAP problems can be difficult to track down. Because you're dealing with the fuel system, it's vapors, and liquid fuel there are specialized tools dealers and good independant shops have.

The latest tool used by the dealer is a "Smoke" machine. This indroduces a vegatable based smoke into a closed fuel tank /EVAP system, pressurizes it with inert gas. The mechanic then looks for leaks.

The ECM is able to detect leaks as small as 0.040 or 0.020" depending upon year of the vehicle. That's about the size of a pencil lead.

Basically, I'd recommend taking it to someone with the equipment and latest service information.

:rolleyes: :rolleyes:


[Modified by torqueman2002, 11:30 PM 6/22/2003]

 

I had this same type code thrown on my 99 Chevy Silverado. Friend of mine who used to be a GM mech told me to replace the gas cap and the code would go away in about 2 weeks. It worked. Don't know if you would be that lucky, but it did work for me

 

I will give the gas cap a try first. Thanks for all the great info torqueman2002 and HWoods.




:cheers: