Ok, getting this started for mdbsat, '03 R53 40K mi. I am going to have to get him to chime-in here. Symptoms include poor fuel economy. Anything else mdbsat? The O2 sensors have been messed with though during the header install. Does this code mean the #1 O2, meaning the one before the cat or rather the front most one? So, my first guess would be to give the O2 sensors a good inspection as I have seen improperly run wires melt and short on a header. If this is the case you may be able to repair the wires, reroute properly and have a cheap fix. Another thing to try is to swap the O2 sensors to observe code changes. Not 100% sure the connectors and wire lengths will allow this though. Anybody know? If in fact an O2 is bad, is it advisable to change them both as the life of the 2nd one can't be far behind the expired O2?