P0401 - Exhaust Gas Recirculation Flow Insufficient Detected
P0443 - Evaporative Emission Control System Purge Control Valve Circuit Malfunction
Diagnostic fault codes never say to replace parts or that they're defective. There's no need to replace "everything", which doesn't tell us anything, because the codes indicate the circuit or system that needs further diagnosis, (443), or it describes the unacceptable operating condition, (401).
Insufficient EGR flow can be caused by a passage blocked with carbon. Code 443 tells you the purge valve circuit needs to be diagnosed. The valve, or any part referenced in a code, is only the cause of that code about half of the time. You also have to look for wiring problems like corroded or stretched connector terminals, wires rubbed through on a sharp metal bracket, and things like that. Mechanics use a scanner to command the Engine Computer to run those things so you can see what does and doesn't work. That's especially useful with this circuit because it doesn't run at low vehicle speeds. That makes testing it in the shop impossible.
Code 443 implies there is an electrical problem with that circuit, but it can also be caused by a mechanical problem. An open circuit in a wire to the valve can be detected, but the code can also mean the computer turned the valve on successfully but didn't see the expected change from the oxygen sensors. The exhaust gas is expected to go rich when fuel vapors are drawn out of the charcoal canister.
Tuesday, January 14th, 2014 AT 7:21 PM