P04F3 code meaning
Catalyst Heater Supply Voltage Bank 2
Powertrain system Generic code P04xx codes Check engine light
What P04F3 means
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. P04F3 concerns the heated catalyst of bank 2 – no production vehicle with two heated catalysts is known. 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.
P04F3 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of P04F3
- Check engine light on (depending on the maker)
- Higher emissions after a cold start
- Otherwise usually unremarkable
Common causes of P04F3
- Most 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
- Less likelyModule or voltage measurement faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Catalyst heater bank2Heater power switchHeater wiringEngine control module
What each part of P04F3 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 4 | Area: auxiliary emission controls (catalytic converter, EGR, EVAP). |
| F3 | The exact fault in that area. |
What to do next
- Note P04F3 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P04F3
What does P04F3 mean?
P04F3 means "Catalyst Heater Supply Voltage Bank 2". 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 a generic code, so it means the same on every make.
Is it safe to drive with P04F3?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P04F3 fail an emissions test?
Yes, it can. P04F3 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P04F3 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P04F3 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.