TORQDEX // POWERTRAIN DTC
Catalyst System Efficiency Below Threshold — Bank 1
Catalyst monitoring indicates that Bank 1 catalytic-converter efficiency is below the expected threshold.
01 // CODE DEFINITION
What P0420 means
P0420 is set when catalyst-monitoring logic determines that the Bank 1 converter is not storing and processing exhaust gases as expected.
A degraded catalyst is common, but exhaust leaks, sensor faults, misfires, or long-term mixture problems should be checked before condemning the converter.
02 // COMMON SYMPTOMS
What you may notice
03 // COMMON CAUSES
What can trigger P0420?
Catalytic converter degradation
The catalyst may no longer store oxygen or process exhaust gases efficiently.
Exhaust leak
Leaks can alter oxygen-sensor readings and catalyst-monitor results.
Oxygen sensor issue
A biased or slow sensor can affect catalyst monitoring.
Underlying engine problem
Misfires, oil consumption, or incorrect fueling can damage or overwhelm the catalyst.
04 // DIAGNOSTIC ORDER
Start here
Check for other engine codes first
Correct active misfire, fuel-trim, or sensor faults before evaluating catalyst efficiency.
Inspect the exhaust system
Check for leaks upstream and around the catalyst and oxygen sensors.
Review oxygen-sensor data
Compare upstream and downstream sensor behavior under appropriate operating conditions.
Evaluate catalyst condition
If supporting systems test correctly, evaluate the converter using appropriate service procedures.
05 // DIAGNOSTIC PRINCIPLE
Confirm the fault before replacing parts
P0420 identifies a condition detected by the vehicle control system. It does not automatically identify one failed component. Test the affected system before replacing parts.
06 // RELATED CODES