Warm Up Catalyst Efficiency Below Threshold Bank 1
2018-2018 Lincoln MKX 2.7L V6 EcoBoost
The 2018 Lincoln MKX is equipped with a 2.7L V6 turbocharged gasoline engine. Below you'll find detailed p0421 diagnostic code information including labor time estimates, cost ranges, and technician notes specific to this engine configuration.
Description
The Bank 1 warm-up catalytic converter is not efficient during the warm-up period.
Symptoms
- Check Engine Light
- Failed emissions test
Common Causes
- Worn catalyst
- Engine running rich during warm-up
- O2 sensor issue
- Exhaust leak
Diagnostic Steps
- Monitor catalyst temps during warm-up
- Compare O2 sensor signals
- Check for exhaust leaks
Repair Notes
Replace warm-up catalyst if confirmed failed.
Related Codes
Other Powertrain Codes
- P0001Fuel Volume Regulator Control Circuit/Open
- P0002Fuel Volume Regulator Control Circuit Range/Performance
- P0003Fuel Volume Regulator Control Circuit Low
- P0004Fuel Volume Regulator Control Circuit High
- P0010Intake Camshaft Position Actuator Circuit/Open Bank 1
- P0011Intake Camshaft Position Timing Over-Advanced Bank 1
- P0012Intake Camshaft Position Timing Over-Retarded Bank 1
- P0013Exhaust Camshaft Position Actuator Circuit/Open Bank 1
- P0014Exhaust Camshaft Position Timing Over-Advanced Bank 1
- P0015Exhaust Camshaft Position Timing Over-Retarded Bank 1
P0421 on Other Vehicles
Lincoln Aviator
2003-2003 4.6L V8 DOHC
Lincoln Aviator
2004-2004 4.6L V8 DOHC
Lincoln Aviator
2005-2005 4.6L V8 DOHC
Lincoln Aviator
2020-2020 3.0L Twin-Turbo V6
Lincoln Aviator
2020-2020 3.0L V6 Twin Turbo
Lincoln Aviator
2020-2020 3.0L V6 Twin Turbo Hybrid
Lincoln Aviator
2021-2021 3.0L Twin-Turbo V6
Lincoln Aviator
2021-2021 3.0L V6 Twin Turbo
Common Questions
What does code P0421 mean on a 2018-2018 Lincoln MKX?
P0421 stands for "Warm Up Catalyst Efficiency Below Threshold Bank 1". The Bank 1 warm-up catalytic converter is not efficient during the warm-up period.
What are the symptoms of P0421 on a Lincoln MKX?
Common symptoms of P0421 include: Check Engine Light, Failed emissions test.
What causes P0421 on a 2018-2018 Lincoln MKX?
Common causes of P0421 include: Worn catalyst, Engine running rich during warm-up, O2 sensor issue, Exhaust leak.
Last updated: March 2026