P2097

P2097 means the ECU has determined that the post-catalyst fuel trim on bank 1 is running too rich — the rear O2 sensor is reading consistently rich over a calibrated window, and the ECU has cut as much fuel as it's allowed to without setting other codes. The cheapest-first ladder: scan-tool the rear O2 voltage at warm idle and during a steady cruise — it should hover around 0.6-0.8V and switch slowly; if it's pinned above 0.85V steady, the post-cat signal is rich. Long-term post-cat trim that swings beyond -15% triggers the code. Check for fuel intrusion into the exhaust ahead of the rear O2 — a leaking fuel injector dumps unburned fuel through the cat, the cat reduces the excess HC and burns it, and the rear O2 reads rich because exhaust oxygen is being consumed. Run a fuel-injector balance/leakdown test: an injector leaking even 5 cc/min when commanded closed is enough to set this code over a long drive cycle. Also check that the front O2 sensor isn't biased rich (a slow-responding front O2 commands too much fuel; the cat can't catch up); front O2 switch rate should be at least 0.5 Hz at 2,500 RPM steady. Verify the EVAP purge valve isn't stuck open and dumping fuel vapor into the intake at idle. The expensive-misdiagnosis caveat: don't replace the rear O2 sensor on a P2097 before ruling out a leaking injector with a $20 noid-light and a fuel-pressure drop test — a stuck-open injector on a GDI engine will throw P2097 plus a fuel-economy complaint, and the rear O2 is downstream of the actual problem.

Vehicle-specific patterns: 2007-2015 Toyota Camry/Avalon/Sienna with the 2GR-FE 3.5L V6 throws P2097 less often than its P2096 sibling but follows the same pattern in reverse — a slowly degrading cat plus a slightly leaky injector tips the post-cat signal rich. 2008-2014 Lexus IS250/IS350 with the 2GR/4GR family throws P2097 from carbon-loaded direct-injection injectors that drip at closed-throttle conditions. 2005-2010 Ford F-150 with the 5.4L 3V Triton sometimes throws P2097 from a stuck-open EVAP purge valve at idle; pinch the purge hose and watch the trim recover before condemning the cat. 2009-2014 Honda Accord/Pilot with the J35 throws P2097 when MDS/VCM cylinders deactivate incorrectly and dump unburned fuel into the exhaust. Estimated repair: $80 (EVAP purge valve) to $1,200 (injector replacement on a GDI Lexus).