2000 Sienna P0420 After Exhaust Repair: Is Muffler Cement Causing the Code?
I have a 2000 Toyota Sienna that has been well maintained since new. The flex pipe, located about one foot from the exhaust converter, was leaking and a local shop replaced it with a stainless braided sleeve. They sealed both ends of the sleeve using a significant amount of muffler cement. Similarly, the exhaust manifold connection is also oozing with muffler cement. No other recent work has been done on the vehicle. A few days later, the OBD2 code P042 or P0420 appeared and was cleared by the shop. The code returned a few days later. Could this exhaust repair — especially the use of excessive muffler cement near the converter — be causing the P0420 fault? Should I simply replace the catalytic converter, or are there other potential issues I should consider before taking further action?
Yes, an exhaust leak near the catalytic converter can trigger a P0420 code. On some vehicles, the flex pipe is part of the original catalytic converter assembly — so replacing just the flex pipe with a braided sleeve may not be sufficient. The proper fix might involve replacing the entire factory-installed converter rather than using a welded-in bandage pipe. Additionally, excessive use of muffler cement can compromise exhaust system integrity and may damage oxygen sensors or their wiring due to heat and chemical exposure during welding or cutting operations.