P04F2

What it means

P04F2 relates to the supply voltage for the bank 1 catalyst heater. The engine control unit monitors the voltage feeding the electrically heated catalyst circuit and has found it outside the expected range. The exact trigger (too high, too low or implausible) depends on the vehicle, so check the manufacturer's data for the model. Few vehicles have an electrically heated catalyst.

Symptoms

• Engine warning light on
• Slower catalyst warm-up, which may raise cold-start emissions
• Possible emissions test failure
• Other charging or battery voltage codes stored alongside it
• Usually no noticeable change in driveability

Possible causes

• Low or unstable battery or system voltage, or a charging system faultlikely
• Corroded, loose or damaged wiring and connectors in the catalyst heater supply circuitlikely
• Blown fuse or faulty relay in the heater supply feedpossible
• Faulty catalyst heater element with abnormal resistance affecting the supply voltage readingpossible
• Poor earth connection on the heater circuit or control unitpossible
• Fault in the engine control unit or heater driver circuitrare

How to diagnose

1. Read all stored codes and freeze frame data, noting battery voltage and engine conditions when the code set
2. Look for related charging, battery or heater circuit codes and deal with those first
3. Test the battery state of charge and the charging system output with the engine running
4. Inspect the relevant fuse and relay, and check the wiring and connectors for damage, corrosion, heat or water ingress
5. Check the heater circuit supply voltage and earth against the manufacturer's wiring diagram
6. Measure the heater element resistance and compare it with the manufacturer's specification
7. Check for any applicable software updates or technical bulletins for the model and engine
8. Clear the code and road test to confirm it does not return

How to fix

• Charge or replace a weak battery and repair any charging system fault
• Repair or replace damaged wiring, connectors or earth connections in the heater circuit
• Replace the faulty fuse or relay after finding why it failed
• Replace the catalyst heater or catalyst assembly if the heater element is faulty, following manufacturer procedure
• Repair or replace the control unit only after wiring and supply faults have been ruled out
• Apply a manufacturer calibration update only if one is documented for this fault

Can I keep driving?

Nearby codes

• P04F1GenericEVAP System Purge Line Performance
• P04F3GenericCatalyst Heater Supply Voltage Bank 2