About P0420 Code

P0420 code refers to the catalyst system efficiency for bank 1 being below threshold for the current engine operating conditions.  This shows up as Check Engine Light error in the instruments panel of a Toyota Sienna dashboard.  A Toyota dealership may charge about $70.00 for performing the relevant diagnostic test, a AutoZone car parts retail store may do this 1 minute test for free.

Probable Causes of P0420 Code

1. Catalytic Converter defective (failure possibly due to #2, 3, or 4)
2. Engine misfire or running condition
3. Large vacuum leak
4. Engine oil leakage into exhaust-valve guide seals, piston rings

First repair for P0420 Code

I dug up information about the existence of a Toyota Technical Service Bulletin (TSB) related to the P0420 Code and the 8 year/80,000 mile emissions warranty.  It is interesting to note that several Toyota owners are not fully aware of this emissions warranty.  With a hard copy of the emissions warranty, I took the Toyota Sienna to a Toyota dealership.  I thought the Toyota dealership would follow the instructions of the Toyota TSB.   Instead, the Toyota dealership replaced the exhaust manifold catalytic converter under the emissions warranty.

Second repair for P0420 Code

Several weeks later the Check Engine Light turned on again.  The Toyota dealership replaced the existing engine control computer with a remanufactured engine control computer under emissions warranty.  The Toyota dealership refused to return the existing engine control computer.

Third repair for P0420 Code

Several weeks later, the Check Engine Light came on again.  This time, the Toyota dealership verified that the engine control computer installed previously was the appropriate one and replaced the front exhaust pipe with converter under goodwill warranty assistance because the Sienna was more than 8 years old but was within the 80,000 mileage.

Lessons Learned

1. I thought the Toyota dealership would play games but they did not.
2. Bad, bad, bad Toyota Sienna.  Never, ever, ever a Toyota Sienna again.

Related EPA Fact Sheet: Emissions Warranties for 1995 and Newer Cars & Trucks