"P0441" Evaporative Emission Control System Incorrect Purge Flow
The "EVAP purge flow" faults are issues between the carbon cannister and the intake. The EVAP leak detection generally concerns the fuel tank to carbon cannister plumbing.
A little background. The EVAP or evaporative emission system is a control system to keep vapors from evaporation in the fuel tank from getting into the atmosphere. The fuel tank is not vented, but rather the vapors are piped to the carbon cannister (usually located behind the pass. Side front wheel) where the charcoal element absorbs the vapor. This is actually a vapor "storage" device. Under certain engine operating conditions, the ECU activates the Cannister Purge Valve (N80) which opens and allows the engine vacuum to suck the fuel vapors back out of the carbon cannister. This purges the vapor, allowing the cannister to absorb more vapor. This evap system has been on vehicles since the '70s.
As part of the OBDII standard effective for 1996 cars and newer, it was mandated that leaks in the systems must be detected and reported as a fault which will set the Check Engine Light (CEL). To detect leaks, the system is pressurized by a pump so that leaks can be detected by a lack of appropriate pressure in the system. If there is a leak, such as a cracked vent hose, loose (or leaky) gas cap, poorly installed or defective O-rings on the fuel level senders on the fuel tank, etc. A code will be set. On the cannister to intake side, leaks are detected by deviations in the idle control system. If you have leaks in the lines from the carbon cannister to the intake, intake leaks, a defective purge valve, etc you will often get purge flow faults.
My first recommendation is to closely inspect all the small vacuum lines connected to the intake manifold. The corrugated plastic lines are often the culprits, as well as the fabricate covered vacuum lines. Also consider replacing the gas cap.
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Wednesday, February 24th, 2010 AT 6:49 AM
