CEL: Catalytic Converter "Poor Efficiency" ???????

[Z600]

Hey guys, long time no post.Got a question for anyone that might have some input.Many, many months back (maybe last year?) I had a CEL pop up outta nowhere while I was hummin' down the road. The local Pontiac dealer was on the way home, so I stopped in and had them check it. Loose gas cap was the culprit, though it had been a few days since I bought gas. Service tech said the seal on the cap may be going bad, and that if happened again I may need to get a new cap. No harm, no foul.Fast forward to last week. Again, driving down the road, and the CEL goes off. This time I'm not so worried. When I get home, I remove/re-tighten the gas cap, and unplug the battery for awhile. Start it up, no more CEL. So, I think I must need a new cap.2 days later the CEL goes off again. I've got to take it in to the dealership anyway to look at my struts (got one leaking), so I have them double check the engine light (this is a different dealership, one that I actually have do all my mechanic work... they've always been super-helpful).THIS time, the code says something about the catalytic converter and "poor efficiency" (dunno the actual code #). They did a pressure test, and there's no clogging evident, just this "poor efficiency" thing. Has anyone else had this? My Vibe's a 2003 model, and I just cleared 111,000 miles. A tech at Advance Auto Parts claims this code can also spawn from a bad gas cap, and I was wondering if anyone could validate him. The dealership wants to replace the whole converter, which is a hefty $720! No way, no how, thank you very much, not for a car I'm ditching next year. ESPECIALLY if it's just a gas cap malfunction.Any light you guys can shed on this would be much appreciated!~Z

[joatmon]

sounds like P0420. I fixed mine with a new converter. http://forums.genvibe.com/zerothread?id=19728 http://forums.genvibe.com/zerothread?id=22020

[Z600]

Yeah, that sounds about right. I don't think I'm gonna get it fixed, though. I bought a new gas cap for $6, and after unplugging the battery, I haven't seen a CEL for a week now. I'm hoping it was just some bad gas, though I know that's probably just wishful thinking. I only need the car to last 1 more year, so I don't see spending $720 just to keep a light from coming on. I'd be better off putting that toward a down payment on my next car.Thanks for the links, though! Very educational.BTW, the fact that you keep track of and build charts for your mileage history freaks me out. ~Z

[ZubenElGenubi]

Sorry that I'm just now seeing your thread. Those "poor efficiency" CELs can also result from a loose or broken vacuum line near the air intake.My sister-in-law's Toyota Echo had these CELs after a service. I used the ScanGauge to read & clear the codes, then found some info on the Internet helping us to diagnose the problem. Found a loose vacuum hose at the back of the air filter box and plugged it back in. No more CELs.It was probably my fault, too, since I checked the air filter before we took the car in for service.Take a good look under your hood and let us know if you find anything.EDIT: here was my initial post about these codes:http://forums.genvibe.com/zerothread?id=25066