P04F9
Catalyst Heater Circuit Intermittent Bank 2
Generic OBD-II
What this part does
The catalyst heater is an electric heating element or system that warms the catalytic converter quickly after a cold start. The engine computer switches it on so the converter reaches working temperature sooner, which cuts the emissions produced right after starting. A fault usually shows as a warning light and does not change how the car drives.
Common symptoms
What you'll notice
- Check and potentially replace the oxygen sensor in Bank 2
- Inspect and repair any wiring issues or loose connections related to the catalyst heater circuit
- Test and replace the catalyst or catalytic converter in Bank 2 if necessary
- Verify and fix any issues with the powertrain control module (PCM) or engine control unit (ECU)
- Perform a thorough inspection and potential repair of the exhaust system in Bank 2
Common causes
Most likely first
- Faulty oxygen sensor
- Malfunctioning catalytic converter
- Damaged or deteriorating wiring or connectors
- Faulty engine control module (ECM)
- Exhaust leak
How to diagnose & fix
Work through it in order
- Loss of engine power or sluggish acceleration
- Engine misfires or stumbles
- Reduced fuel efficiency
- Check Engine Light illuminates
- Strong smell of rotten eggs (sulfur) from the exhaust
Related codes
Read & clear P04F9 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
Need a scanner that reads ABS, airbag and more? GaragePro OBD scan tools ship worldwide. See scanners →