Wiring fault in the catalyst heater circuit, such as a short to voltage or chafed insulation; Corroded, loose or damaged connector at the heater, relay or control unit; Faulty catalyst heater element or its internal circuit; Faulty heater relay or power supply, or a blown or incorrect fuse where fitted; Faulty heater driver within the engine control unit or secondary air or heater control module; Outdated control unit software that is a known cause for this fault on a specific model.

P04F6

Catalyst Heater Circuit High Bank 1.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
4: AreaAuxiliary emission controls
F6: FaultThe specific fault in that area

What it means

P04F6 is a generic powertrain code meaning the control unit has detected a high signal in the catalyst heater circuit for Bank 1. The heater is used to bring the catalytic converter up to working temperature quickly after a cold start. The control unit monitors the heater driver circuit and set the code when the voltage or current was higher than expected, or did not match the command it sent.

Symptoms

Engine warning light on
Possible increase in cold-start emissions or a failed emissions test
Slightly higher fuel consumption in some cases
Other catalyst or heater related codes stored alongside it
Usually no noticeable change in drivability

Possible causes

Wiring fault in the catalyst heater circuit, such as a short to voltage or chafed insulationlikely
Corroded, loose or damaged connector at the heater, relay or control unitlikely
Faulty catalyst heater element or its internal circuitpossible
Faulty heater relay or power supply, or a blown or incorrect fuse where fittedpossible
Faulty heater driver within the engine control unit or secondary air or heater control modulerare
Outdated control unit software that is a known cause for this fault on a specific modelrare

How to diagnose

Read all stored and pending codes and record the freeze frame data, noting engine temperature and conditions when the code set
Check for related codes covering the catalyst, oxygen sensors, battery voltage or other heater circuits, and deal with those first
Look up the catalyst heater circuit layout for the specific model and engine, as the heater type, location and control differ between vehicles
Visually inspect the wiring and connectors from the heater to the relay and control unit for chafing, heat damage, water ingress and corrosion
Check the fuse and relay supply and earth, and measure battery and supply voltage at the heater connector with the circuit active
Measure the heater element resistance and compare it with the manufacturer specification, and test the circuit for shorts to voltage
Command the heater with a scan tool if supported and monitor the driver signal and response
Check for a manufacturer software update or technical bulletin for this fault on the vehicle in question

How to fix

Repair or replace damaged wiring and fix any short to voltage in the heater circuit
Clean, repair or replace corroded or damaged connectors and terminals
Replace the catalyst heater or catalytic converter assembly if the heater element is faulty and the heater is not serviced separately
Replace a faulty relay or fuse after finding out why it failed
Replace or repair the control unit only after the wiring, supply and heater have been proven good
Update the control unit software if an update is available for a known fault

Can I keep driving?

Low severity

The car can normally be driven while you arrange a repair, as this fault mainly affects cold-start emissions. Do not leave it for long, as it may cause an emissions test failure and the cause could be an electrical fault that gets worse.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.