OBD-II Diagnostic Trouble Code
P0421
Warm Up Catalyst Efficiency Below Threshold Bank 1
P
Powertrain
engine / trans
engine / trans
0
Generic
SAE standard
SAE standard
4
Auxiliary emission controls
21
Warm Up Catalyst Efficiency Below Threshold Bank 1
Severity · general guide
Moderate
Fix soon — usually won't strand you
Code type
Generic
System
Powertrain
Standard
ISO/SAE Controlled
Fault type
General