OBD-II code · Powertrain (generic)
P0423 Heated Catalyst Efficiency Below Threshold (Bank 1)
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.
Is it safe to drive with P0423?
Usually safe for short trips, but don’t ignore it: the underlying fault can get more expensive over time.
Common causes
- Most likelyCatalyst aged or contaminated
- PossibleCatalyst heater circuit fault
Symptoms
- Check engine light on
- Failed emissions inspection
- Possibly slightly increased fuel consumption
- Sulfur (rotten egg) smell from exhaust under load
Repair at a glance
- Difficulty
- Hard
- DIY friendly
- Best left to a mechanic
- Typical labour
- 1.5–5 h
- Emissions test
- Likely to fail
- After the fix
- A drive cycle is needed before the light stays off
- Parts involved
- Heated Catalyst, Catalyst Heater, Oxygen Sensor Downstream
Related codes
- P0420Catalyst System Efficiency Below Threshold (Bank 1)
- P0433Heated Catalyst Efficiency Below Threshold (Bank 2)
- P0421Warm Up Catalyst Efficiency Below Threshold (Bank 1)
- P0422Main Catalyst Efficiency Below Threshold (Bank 1)
- P0424Heated Catalyst Temperature Below Threshold (Bank 1)
- P0425Catalyst Temperature Sensor (Bank 1, Sensor 1)
- P0426Catalyst Temperature Sensor Circuit Range/Performance (Bank 1 Sensor 1)
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.