Scion XB 2006 P0420 with rich fuel trim

Hey everyone, am new to this forum. My question is about a 2006 Scion XB manual with 230k miles. I get the DTC of P0420. I have a scanner with live data and the o2 sensors seem to work fine. What I do notice is that the Long FT runs low. When at 2500rpm it reads somewhere from -18% to -19.5%. Yikes. The temperature of the cat look the same pre and post. If I could get help with a direction to diagnose this.

The car runs fine, no problems that I feel. No hesitation, no high rpm at idle. Nothing that really sticks out as abnormal. Also, this light has been on for maybe a year. There was another DTC with the P0420 a year ago, P0012, which read Camshaft Position "A" - Timing Over-Retarded. I Checked the OCV oil control valve and it snapped in half. My brother replaced it 5 years ago with an autozone part. Changed it with an OEM, erased the codes and the P0012 has not come on.

Hey Salvatierra, welcome! I see that the long term trims are definitely running rich. What are the short terms doing at 2500? Interested to know if they're bouncing around 0%, or if they adding to/subtracting from the long term correction.

Any other performance issues noted? Misfire, hesitation, low power?

My first thought is to look at the MAF, potentially overreporting. What's the g/s reading from the MAF at hot idle, with no accessories on?

I'm not familiar with a Scion but, with fuel trims that negative, active O2 sensors, and no noticeable drive-ability issues, is it a possibility that a vacuum activated fuel pressure regulator is leaking fuel into the intake vacuum?

The freeze frame data had the MAF at 16.46g/s with rpms at 2927 and Long FT at -18. This morning I checked live data and the MAF at idle is at 1.5g/s and at 2600rpms it is at 6.5g/s.

The car runs fine. Maybe it feels low powered but I thought it was because it is a 1.5 engine