P04F5

What it means

P04F5 means the engine control unit has found the catalyst heater circuit for bank 2 reading lower voltage or current than expected. The heater warms the catalytic converter quickly after a cold start so it cleans the exhaust sooner. The unit sets the code when its self-check of the heater circuit or driver sees a low signal, such as a short to ground or a fault in the supply. The exact layout of the circuit and the test conditions depend on the model and engine.

Symptoms

• Engine management warning light on
• Possible increase in cold-start emissions or a failed emissions test
• Related catalyst efficiency or heater codes stored alongside it
• Possible slight rise in fuel consumption on cold starts
• Usually no noticeable change in driveability

Possible causes

• Wiring to the bank 2 catalyst heater chafed, shorted to ground or damaged by heatlikely
• Corroded, loose or water-contaminated connector at the heater or control unitlikely
• Internal short or failed heating element in the bank 2 catalyst or heater assemblypossible
• Blown fuse or faulty heater relay or supply feedpossible
• Low battery or charging system voltage affecting the circuit readingpossible
• Fault in the heater driver inside the engine control unitrare

How to diagnose

1. Read all stored codes and freeze frame data, noting engine temperature, battery voltage and whether other heater or catalyst codes are present
2. Check battery condition and charging voltage, as low supply voltage can upset circuit monitoring
3. Look at the fuse and relay for the catalyst heater circuit using the vehicle wiring diagram, as the layout varies by model
4. Inspect the bank 2 heater wiring and connectors for chafing, heat damage, water ingress and corrosion
5. Check the circuit for a short to ground and for resistance and continuity, following the manufacturer's procedure
6. Measure the heater element resistance against the manufacturer's specification
7. Check for supply voltage and driver operation at the connector while the control unit commands the heater, if the procedure allows
8. Clear the code and road test to confirm whether it returns, then recheck freeze frame data

How to fix

• Repair or replace damaged wiring and fix any short to ground
• Clean, repair or replace corroded or damaged connectors and terminals
• Replace a blown fuse only after finding and fixing the cause, or replace a faulty relay
• Replace the bank 2 catalyst or heater assembly if the element is shorted or out of specification
• Repair the battery or charging system if supply voltage is low
• Repair or replace the control unit only if the driver fault is confirmed after all other checks

Can I keep driving?

Nearby codes

• P04F4GenericCatalyst Heater Circuit Low Bank 1
• P04F6GenericCatalyst Heater Circuit High Bank 1