OBD-II code · Powertrain (generic)
P04F2 Catalyst Heater Supply Voltage Bank 1
The electric catalyst heater on bank 1 - used on hybrids and modern petrol cars to bring the catalyst above light-off temperature within seconds of cold start - reports that its supply voltage is outside the expected window. The heater cannot deliver the rated power, so cold-start emissions rise until the catalyst reaches light-off conventionally.
Is it safe to drive with P04F2?
Usually safe for short trips, but don’t ignore it: the underlying fault can get more expensive over time.
Common causes
- Most likelyHeater supply voltage low or unstable
- PossibleDC/DC converter fault on heater rail
- Less likelyHigh contact resistance in supply
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
- 2–6 h
- Emissions test
- Likely to fail
- Parts involved
- Electric Catalyst Heater B1, High Voltage Supply, Dc Dc Converter
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.