OBD-II code · Powertrain (generic)
P04F9 Catalyst Heater Circuit Intermittent Bank 2
Same as P04F8 on bank 2. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
Is it safe to drive with P04F9?
Usually safe for short trips, but don’t ignore it: the underlying fault can get more expensive over time.
Common causes
- Most likelyIntermittent contact at connector
- Less likelyConnector with intermittent contact under vibration
- Less likelyHarness routed against vibrating component
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
- 1–4 h
- Emissions test
- Likely to fail
- Parts involved
- Electric Catalyst Heater B2, Catalyst Heater Wiring B2
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.