P0423 Code: Heated Catalyst Efficiency Below Threshold (Bank 1)
🟠 Moderate severity · drivable
Drivable, but the heated catalytic converter isn't cleaning exhaust efficiently and may need attention.
What P0423 means
The heated catalytic converter on bank 1 isn't cleaning the exhaust as well as it should. These converters use an electric heater to reach working temperature faster, and this code means the converter isn't performing as expected.
Symptoms
- Check engine light is on
- Reduced fuel economy
- Possible failed emissions test
- Often no noticeable driving symptoms
Common causes
- most common: Failing heated catalytic converter
- common: Faulty oxygen sensor
- less common: Faulty catalyst heater circuit
How to fix it
| Fix | DIY? | Typical cost |
|---|---|---|
| Test the oxygen sensors and replace any that are faulty | Yes | $60–200 |
| Check the catalyst heater circuit and fuses | Mechanic | $50–150 |
| Replace the heated catalytic converter | Mechanic | $600–2500 |
Frequently asked questions
Can I drive with a P0423 code?
Yes, but the heated converter isn't cleaning exhaust efficiently. Get it diagnosed before your next emissions test.
What is the most common cause of P0423?
A failing heated catalytic converter, though a bad oxygen sensor can also trigger it.
How much does it cost to fix a P0423?
$60–$200 for an O2 sensor, or $600–$2,500 for a new heated catalytic converter.
Related codes
P0424
P0424 Code: Heated Catalyst Temperature Below Threshold (Bank 1)
P0422P0422 Code: Catalyst 2 Efficiency Below Threshold (Bank 1)
P0420P0420 Code: Catalyst System Efficiency Below Threshold (Bank 1)
Updated 2026-08. This page is informational and not a substitute for professional diagnosis.