P0418 SUBARU - Secondary Air Injection System Relay 'A' Circuit Malfunction
- Faulty Air Pump inoperative
- Air bypass solenoid harness is open or shorted
- Air bypass solenoid circuit poor electrical connection
When is the code detected?The DTC P0418 is detected the the AIR vacuum control solenoid circuit not operating as desired by the PCM.
- Engine Light ON (or Service Engine Soon Warning Light)
- Engine hesitation
P0418 Subaru DescriptionAn air pump is used on the vehicle to lower tail pipe emissions on start-up. The Powertrain Control Module (PCM) grounds the Air pump relay control circuit which energizes the Air pump. The PCM also grounds the Air combination valve vacuum control solenoid circuit, which energizes the Air vacuum control solenoid. Vacuum is then applied to both Air combination valve diaphragms which opens the shut off valves. The PCM enables both circuits simultaneously when Air system operations id desired. When the AIR system is active, then Air pump forces fresh air into the exhaust stream in order to accelerate catalyst operation. The AIR combination valves replace the conventional check valves. When the AIR system is inactive the shut off valves prevent air flow in either direction.
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