P04F2Catalyst Heater Supply Voltage 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. P04F2 concerns the heated catalyst of bank 1. The code monitors the supply voltage of the heater: if it lies outside its window when heating is requested, the heater cannot deliver its power and is limited or switched off, so the catalyst lights off later. A Subaru patent detects faults in the supply path when the heater is commanded. 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
- Likely48 V or high-voltage supply weak (battery, charge, cold, DC-DC converter)
- PossibleFuse, relay or power switch faulty
- PossibleContact resistance or corrosion at high-current connector or ground
- RareModule or voltage measurement 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: €80 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.