I have a 2004 XC90 2.5T AWD with 176,000 miles.
First, I started noticing that the driver information display would sometimes say "Fuel filler cap open / loose" even though the cap was always secure and the cap appears to have no cracks or torn gaskets.
Later, my check-engine light came on. I pulled the codes and am getting the following:
ECM-4338 Leak Diagnostic
ECM-400C Fuel tank system, leakage
ECM-130A Intake air leakage faulty signal

Every time I clear the codes, they eventually come back. The car drives with no issues.
What could be going on, and how do I investigate?

 

ECM 4338 suggests a problem with your gas tank filler cap (meaning the here's pressure leaking..)
ECM 400C says Fuel tank system, leakage and/or three-way catalytic converter (TWC) efficiency, bank 1. Signal too high
ECM 130A can be an Intake air leakage, faulty signal or Mass air flow (MAF) sensor, faulty signal, mass air flow. Signal too high or mass air flow. Signal too low

So somewhere pressure is leaking out of the fuel system - do you ever smell gas when filling up? Could be the seal around the filler neck or the fuel pump. The intake air leak could be a simple vacuum hose or a actuator with a torn diaphram.

Just wonding how these two could be related - possibly something in the evap system?? Normally evap problems have their own codes but you may want to check for the vacuum lines around the charcoal cannister and other lines that connect to the tank.

 

I decided to look at the generic OBDII codes instead of the Volvo-specific codes. There was only one - P0455 - Evaporative emission system leak detected, large leak. So your guess about a problem with the EVAP system seems to be correct. I started looking under the hood and noticed this part (on the driver side) which had its lower and upper halves separated. I don't know what this is or if it has anything to do with the EVAP system. Could this be my problem?



What is this part? Notice that it is loose and that the top half is probably supposed to be connected to the bottom half.

Here is the part with the two halves separated. The plastic is cracked, and there is debris within

 

Answering my own question here. The broken part appears to be the brake booster vacuum switch. I don't think this is part of the EVAP system, so something else must be wrong. Anyway, I guess I better fix the switch.