OBD-II code · Powertrain (generic)
P04F8 Catalyst Heater Circuit Intermittent Bank 1
Same as P04F4 with intermittent or erratic signal - typically a connector or harness fault on the heater feed.
Is it safe to drive with P04F8?
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 B1, Catalyst Heater Wiring B1
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.