P0401 and P0440

[245Trioxin]

I have a 2000 GP GTP with ~91K miles and I have codes P0401 "insufficient EGR flow" and P0440 "Evap system fault."

The codes seem to be connected in some way because I've made a few changes and after every change both codes go away only to return soon thereafter.

I started by cleaning the EGR valve, replaced the PCV valve, replaced the fuel cap, replaced a vacuum hose that goes from the throttle body to the canister purge valve, and finally replaced the canister purge valve. I've also inspected all vacuum lines from the EVAP canister to the engine compartment.

I'm wondering what would cause both codes to be joined at the hip since like I mentioned, they come and go in pairs. What else should I inspect?

[richtazz]

A P0401 rarely indicates a bad EGR valve. Usually , this code is tripped due to a vacuum leak at the engine. The most common cause is the vacuum lines to the MAP sensor, or the lower o-ring on the PCV valve wasn't replaced when the PCV was changed.

P0440 is a difficult code to pinpoint the source. This DTC is set when the PCM commands the EVAP system closed and then monitors the fuel tank pressure sensor to see if the system can hold vacuum pressure. In other words, anything from a bad gas cap to a leaking vacuum hose to a sticking, dirty or failed EVAP canister valve/purge solenoid can cause.