What it means
Same as P04F4 with intermittent or erratic signal - typically a connector or harness fault on the heater feed.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The bank 1 catalyst heater circuit powers or controls the heater for the catalytic converter on bank 1. This code means the control module sees an erratic or intermittent circuit signal, often when a connector or harness loses contact with vibration.
Common causes
Most likely first.
- Intermittent contact at connector
- Connector with intermittent contact under vibration
- Harness routed against vibrating component
Symptoms
- Check engine light on
- Possible increase in cold-start emissions
How to diagnose it
- Save freeze-frame data and check when the bank 1 heater circuit fault occurred, including whether it followed a cold start or vehicle movement.
- Power down the system as directed by the manufacturer, then inspect bank 1 heater connectors for looseness, corrosion, moisture, or damaged terminals.
- Trace the bank 1 heater harness for chafing or contact with a vibrating or hot component, and check its routing and retaining clips.
- Use a scan tool to monitor bank 1 heater circuit status while carefully moving accessible sections of the harness, following the manufacturer's procedure.
- If the intermittent fault persists, test connector pin fit and circuit continuity while flexing the bank 1 harness as specified by the manufacturer.
Common fixes
- Secure a loose bank 1 heater connector and restore its terminal contact.
- Clean corroded bank 1 heater connector pins or replace damaged terminals.
- Repair chafed bank 1 heater wiring and secure the harness away from vibrating components.
- Replace a bank 1 heater connector that loses contact intermittently.
Can I keep driving?
The fault can interrupt bank 1 heater operation and increase cold-start emissions; normal driving may remain possible if the engine runs normally. Arrange diagnosis soon, and take extra care around high-voltage components on hybrid vehicles.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.