P04F2: Catalyst Heater Supply Voltage Bank 1
The electric catalyst heater on bank 1 - used on hybrids and modern petrol cars to bring the catalyst above light-off temperature within seconds of cold start - reports that its supply voltage is outside the expected window. The heater cannot deliver the rated power, so cold-start emissions rise until the catalyst reaches light-off conventionally.
What P04F2 means
P04F2 is a generic OBD-II powertrain code in the emissions group. Bank 1 is the side of the engine with cylinder 1 (inline engines only have bank 1).
- Check engine light
- Usually on
- Emissions-related
- Yes — can fail inspection
- Limp mode possible
- Not typical
- Drive cycle to clear
- Not required
Get it fixed
Post this code once and get quotes from local mechanics. Free to post.
Makes the repair and parts links below specific to your car. Kept in this browser only.
Symptoms
- Check engine light on
- Failed emissions inspection
- Possibly slightly increased fuel consumption
- Sulfur (rotten egg) smell from exhaust under load
Common causes
- 01Heater supply voltage low or unstableMost likely
- 02DC/DC converter fault on heater railPossible
- 03High contact resistance in supplyLess likely
Can I drive with P04F2?
Usually yes, for a short time.
The car will often drive normally, but get it diagnosed soon. Left alone it can raise fuel use and emissions and will fail an OBD inspection. If you notice rough running, warning lights flashing, overheating or a burning smell, stop driving.
Why we rate it moderate
- Turns on the check engine light
- Emissions-related: will usually fail an OBD inspection
Severity is our rule-based rating from the code’s flags in OBDex and the system it affects, not an inspection of your car. If the check engine light is flashing, or you notice overheating, low oil pressure, or brake or steering problems, stop driving and get help.
How to diagnose P04F2
- 1
Confirm the code and save freeze-frame data
Read the codes with an OBD-II scan tool and note every code, not just P04F2. Save the freeze-frame data (speed, load, temperature when the fault set) before clearing anything; it tells you when the fault happens.
- 2
Check for related codes first
Look for P04F3. Related codes often share a cause; a circuit or sensor code usually needs fixing before a performance code like this one.
- 3
Test the circuit
Inspect the wiring and connector at the electric catalyst heater bank 1 and high voltage supply for damage, corrosion or chafing. With a multimeter, check supply voltage, ground and signal against the specifications in the service manual for your vehicle.
- 4
Test the likely causes in order
Start with the most likely cause and work down: Heater supply voltage low or unstable; DC/DC converter fault on heater rail; high contact resistance in supply. Test before replacing parts.
- 5
Check for recalls and service bulletins
Look up recalls for your exact vehicle with its VIN, and ask a dealer about technical service bulletins (TSBs). Manufacturers sometimes issue software updates or extended warranties for known faults.
- 6
Clear the code and verify the repair
After the repair, clear the code and drive the car under the conditions in the freeze-frame data to confirm it does not return.
P04F2 repair cost estimate
Estimate, not a quote. Labor times are typical ranges for this code from OBDex, and $125/hr is an assumed rate. Shop rates and labor times vary by vehicle and region. Diagnosis time may be billed separately.
- DIY difficulty
- Hard
- Good DIY job?
- Usually a shop job
Involved testing or major parts. Most owners use a shop.
Parts and systems involved
- Electric catalyst heater bank 1
- High voltage supply
- DC DC converter
P04F2 FAQ
What does P04F2 mean?
P04F2 means “Catalyst Heater Supply Voltage Bank 1”. The electric catalyst heater on bank 1 - used on hybrids and modern petrol cars to bring the catalyst above light-off temperature within seconds of cold start - reports that its supply voltage is outside the expected window. The heater cannot deliver the rated power, so cold-start emissions rise until the catalyst reaches light-off conventionally.
Is P04F2 serious? Can I keep driving?
We rate P04F2 as moderate severity. Usually yes, for a short time. The car will often drive normally, but get it diagnosed soon. Left alone it can raise fuel use and emissions and will fail an OBD inspection. If you notice rough running, warning lights flashing, overheating or a burning smell, stop driving.
What causes P04F2?
The most common causes, from most to least likely: Heater supply voltage low or unstable; DC/DC converter fault on heater rail; High contact resistance in supply. Test before replacing parts, because several causes can set the same code.
How much does it cost to fix P04F2?
Typical labor is about $250–$750 at an assumed $125/hour shop rate, plus parts. That is an estimate, not a quote: labor times and rates vary by vehicle and region, and diagnosis may be billed separately.
Can I fix P04F2 myself?
DIY difficulty is hard. Most owners leave this to a shop because it needs involved testing or specialist tools. Always confirm the cause before buying parts.
Will P04F2 clear itself?
If the fault was intermittent, the warning may go off once the computer stops seeing it, but the code stays in memory. Fix the cause; clearing the code alone doesn’t repair anything.