I've had a CEL on for a while , it's the dreaded P0411! I've checked the hoses and replaced a few it went away for a while but came back! Been told to change the air pump but i don't have a Vag , can i check the pump any other way? Does it make a sound on start up? I also have a thumping coming from the rear end ,could this be a fuel pump on it's way out?