Join Date: Jan 2007
Location: Southern Ca
Car: 00 OB 07 OBXT
Feedback Score: 0 reviews
To the OP,
Could be either a front o2 sensor, PCV valve or an intake or exhaust leak.
Check the easy cheap stuff first. You don't mention doing anything since the tuneup 10k miles ago ... check the PCV valve, clean it, make sure it's not sticking [I had the same issue, long trips it would code... turned out the PCV was dirty enough to stick and allow enough extra air in to the system to code]
Check that there are no leaks in your relatively new exhaust, bolts can loosen up with heating cooling and vibration. The extra air from an exhaust [or intake] leak will give the same result ... the sensor is showing too much unburned o2.
When the sensor sees extra O2 in the exhaust stream, it's first response is to add extra fuel to increase the combustion of the o2. If it can't add enough to "make it go away", it assumes the cat must be defective. If the leak is in the intake manifold, it generally will be able to add enough fuel to "make it go away" but, generally the leak is on 1-2 cylinders and the ECU adds fuel to all so ... you'll have a couple running rich. If it's the exhaust, it can add fuel all day long but since the o2 is coming in after the cylinder, it doesn't burn and it makes the whole thing worse.
So, check for intake and exhaust leaks [if the car has a MAF, check the ducting from the MAF all the way to the cylinder]. PCV.