OBD-II code · Powertrain (generic)
P04F4 Catalyst Heater Circuit Low Bank 1
The control or supply line to the electric catalyst heater on bank 1 is shorted to ground or measures below the expected voltage when the heater is commanded on.
Is it safe to drive with P04F4?
Usually safe for short trips, but don’t ignore it: the underlying fault can get more expensive over time.
Common causes
- Most likelyControl line shorted to ground
- PossibleHeater element internally shorted
- Less likelyConnector pins corroded - high contact resistance
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
- Parts involved
- Electric Catalyst Heater B1, Catalyst Heater Wiring B1
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.