What it means
Heated (electrically warmed) catalyst on bank 1 fails efficiency monitoring. In addition to standard catalyst aging, faults in the catalyst heater control or supply can cause this code.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The Bank 1 heated catalyst uses an electrical heating system to help the catalyst reach effective operating conditions sooner. The control module monitors the heated catalyst's efficiency and sets P0423 when it falls below the monitored threshold; catalyst aging and a heater supply or control fault can both contribute.
Common causes
Most likely first.
- Catalyst aged or contaminated
- Catalyst heater circuit fault
Symptoms
- Check engine light on
- Failed emissions inspection
- Possibly slightly increased fuel consumption
- Sulfur (rotten egg) smell from exhaust under load
How to diagnose it
- Review freeze-frame data and check for related heater, catalyst-temperature, oxygen-sensor, misfire, and fuel-trim codes.
- Inspect the Bank 1 heated catalyst wiring and connectors for heat damage, corrosion, loose terminals, or exhaust leaks.
- Use a scan tool to check the heater command and available temperature or oxygen-sensor data during the conditions when the monitor runs.
- Test the heater power, ground, and control circuit against the manufacturer's specification before condemning the catalyst.
- If the heater and related sensors work correctly, assess Bank 1 catalyst efficiency using the manufacturer's diagnostic procedure.
Common fixes
- Repair damaged or loose wiring and connectors in the Bank 1 catalyst heater circuit.
- Correct exhaust leaks or engine misfires that affect catalyst monitoring.
- Repair or replace a confirmed faulty heater control or supply component.
- Replace the Bank 1 heated catalyst if testing confirms low efficiency with a functioning heater circuit.
Can I keep driving?
The vehicle may be driven gently if it runs normally, but it is likely to fail an emissions inspection. Avoid heavy loads if the exhaust smells strongly of sulfur or power declines, and investigate any misfire quickly to limit catalyst damage.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.