P05F4: The exhaust-aftertreatment power-relay control circuit is low.
Meaning, symptoms, causes and checks
The exhaust-aftertreatment power-relay control circuit is low. The code concerns relay control and does not specify which aftertreatment component is affected downstream.
Affected system: Powertrain
Symptoms
- Warning light may illuminate
- Related system function may be impaired
- Vehicle-specific symptoms vary
Possible causes
- Low or unstable supply voltage, fuse or relay fault, poor ground, or wiring damage
- Related wiring, connector, power or ground fault
- Vehicle-specific mechanical or control issue
What to check
- Record stored and pending codes and freeze-frame data
- Measure battery and charging voltage under load and compare with scan data; test the named circuit, fuse, relay, grounds and connectors.
- Confirm measured values against the vehicle service information
- Retest under the conditions that set the code
- Measure battery and charging voltage under load and compare with scan data; test the named circuit, fuse, relay, grounds and connectors.
- Repair the verified cause and confirm the code does not return
Also written as: P05F4-00, P05F400, PO5F4 (some scan tools add the fault-type byte, e.g. -00).