2003 Acura MDX P0134 to P0172: Fuel Rich Issue After O2 Sensor Replacement
My 2003 Acura MDX has developed a persistent issue after recently displaying fault code P0134 (Bank 1 Sensor 1) for three weeks. I replaced the Bank 1 Oxygen Sensor 1, but now the vehicle is showing P0172 — System Too Rich (Bank 1). The car emits black smoke from the exhaust, the engine light remains on, and acceleration feels weak. When engaging the AC, RPM drops significantly, causing the engine to shake and nearly stall. In Drive or Reverse, power is noticeably lacking. A local mechanic suggested a clogged catalytic converter in Bank 1 needs replacement, but this typically requires a muffler shop — which seems unusual for a P0172 diagnosis. I'm concerned about spending money on parts that may not be the root cause. Can anyone confirm whether a faulty catalytic converter is actually responsible for P0172? Or could this be related to vacuum leaks, mass airflow issues, or fuel system problems? I'd appreciate any technical insight or diagnostic advice before investing in repairs.
After replacing the Bank 1 O2 sensor, has the P0134 code disappeared? The current P0172 (System Too Rich) suggests a fuel delivery or air intake issue. Without verified fuel pressure readings and proper use of a scan tool to monitor live data, diagnosing the root cause is difficult. A clogged catalytic converter is not a typical fix for P0172 — that code usually points to issues like vacuum leaks, mass airflow sensor faults, or incorrect fuel trim settings. If the auto shop claims abnormal back pressure before Bank 1, they should provide evidence and be willing to stand by their diagnosis. If you're not doing DIY work and want to avoid costly repairs, it's essential to visit a reputable mechanic who can perform proper diagnostics and resolve the issue effectively in one go.