What does OBD2 code P0421 mean?+
P0421 stands for Warm Up Catalyst Efficiency Below Threshold Bank 1. The ECM has detected that the Bank 1 catalytic converter is not reducing exhaust emissions as efficiently as expected, based on comparing the pre-catalyst and post-catalyst oxygen sensor readings.
What causes code P0421?+
Aged or poisoned catalytic converter; O2 sensor fault giving false reading; Exhaust leak before catalyst; Engine oil or coolant burning
How do I fix code P0421?+
Verify with known-good O2 sensors; Check for exhaust leaks before cat; Test for oil or coolant burning; Replace catalytic converter
How much does it cost to fix P0421?+
Estimated repair cost for P0421 is $500–$2000.
Is P0421 DIY-friendly?+
P0421 typically requires professional equipment and a qualified mechanic.
