Warm Up Catalyst Efficiency Below Threshold (Bank 1)
A code P0421 may mean that one or more of the following has happened:
The catalytic converter is no longer functioning properly An oxygen
sensor is not reading (functioning) properly A sparkplug is fouled up
Measure the voltage at the oxygen sensor on Bank 1 (the rear sensor, or
the sensor after the converter).
In fact, it would be a good idea to
test each oxygen O2 sensor while you're at it. One thing to note is that
many vehicle manufacturers offer a longer warranty on emissions-related
parts. So if you have a newer car but it's out of it's bumper-to-bumper
warranty, there still may be warranty on this type of problem.
manufacturers give a five year, unlimited mileage warranty on these
items. It's worth checking into.