I've got an 06 WRX Impreza Wagon with 96k miles that Subaru dealers can't figure out what is causing the issue. I have not modified this vehicle, maintained it well with all services, and have never taken it off road.
At the 75k mark, I received a check engine light giving a PO420
Catalyst System Efficiency Below Threshold error. I brought it in for service at dealer and they said it was an 02 valve issue and at the time it was under warranty and they replaced it with no charge.
The check engine light went away but came back on after another 8,000 miles, but as soon as I would get ready to bring it in to a shop it would go away for another 4 months. This on/off cycle repeated for the next 7000 miles, never staying on longer than a few days at a time.
At 90k mark, the check engine light stayed on permanently. Brought it into a different subaru dealer (I had moved to a different state) and had them do check the code - it was the same PO420 They said it was an O2 Valve causing the issue and the original dealer had not fixed it. I tried calling the original dealer but they said the fix was out of warranty. Spent 1500 for the 90k service and new O2 Valves.
Now at 95k the check engine light has come on again. Just checked the code - it's the same PO420...and a new issue has popped up on a cold start, the engine makes a loud fuzzy noise for about 1 minute (RPMs won't make it go away), and then disappears.
Had a mechanic look at it and he said all my belts look good.
- Do I need a new catalytic converter?
- Is the fuzzy noise maybe related to catalytic problem?
- Do I have a lemon?
Thanks in advance for anyone's help!!!