P04F4Catalyst Heater Circuit Low Bank 1
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- An electrically heated catalyst has a heating disc ahead of the catalyst so that it works soon after a cold start; Emitec's EMICAT runs on 12, 24 or 48 V and draws up to about 300 A. It is in series production on 48-volt mild-hybrid diesel vans since 2022. P04F4 concerns the heated catalyst of bank 1. The code means the measured voltage or current in the heater circuit is too low for the commanded state – typically the feed or the heating element is shorted to ground; depending on the driver also an open circuit. The heater is switched off. No manufacturer document available to us uses this code – Ford, for example, states that heated catalyst monitoring is not supported – so thresholds and warning-lamp logic are not documented; the description follows CARB and patents for the same part.
- What you may notice
- Check engine light on (depending on the maker)
- Higher emissions after a cold start
- Otherwise usually unremarkable
- Likely causes
- LikelyFeed shorted to ground (chafed at the exhaust, heat)
- PossibleHeating disc shorted to its housing (insulation damage)
- PossibleConnector wet or corroded
- RarePower switch or module faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €100 – €2,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.