P0418 on Subaru
Secondary Air Injection System Relay A Circuit
P0418 on Subaru vehicles indicates secondary air injection system relay a circuit. Au7o has documented this code across 1 Subaru model — most commonly on WRX. This code means the Engine Control Module detected a fault in the control circuit for Secondary Air Injection (AIR) System Relay 'A'. The secondary air injection system pumps fresh air into the exhaust during cold starts to help the catalytic converter heat up faster and burn off pollutants, and Relay A switches power to that air pump. P0418 sets when the computer commands the relay but sees an abnormal voltage or no response on its control circuit. This is an emissions-related fault that may keep the air pump from running when needed. Typical repair costs on Subaru range from $700 to $2,200, depending on the specific model and root cause.
Common Causes of P0418
- •Faulty secondary air injection relay (Relay A)
- •Open, shorted, or corroded relay control wiring
- •Poor power or ground feed to the relay
- •Failed secondary air injection pump (drawing wrong current)
- •Corroded relay socket or connector
- •Blown fuse in the air injection circuit
- •Faulty ECM relay driver
P0418 on Subaru by Model
Subaru WRX(1 issue)
- Secondary Air Injection Pump and Switching Valve Failure Triggering CEL and Limp Mode2006-2014
Turbo EJ255/EJ257 WRX models equipped with the secondary air injection system commonly develop failures of the air pump, pressure sensor, or the air switching valves. Moisture intrusion and corrosion can cause the valves to stick or the pump to seize, which sets emissions faults and on many cars can reduce power or force a limp-home condition. Owners typically report a check-engine light shortly after cold start, often with rough cold operation or an audible pump noise before failure.
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What does P0418 mean on Subaru?▼
P0418 stands for "Secondary Air Injection System Relay A Circuit." This code means the Engine Control Module detected a fault in the control circuit for Secondary Air Injection (AIR) System Relay 'A'. The secondary air injection system pumps fresh air into the exhaust during cold starts to help the catalytic converter heat up faster and burn off pollutants, and Relay A switches power to that air pump. P0418 sets when the computer commands the relay but sees an abnormal voltage or no response on its control circuit. This is an emissions-related fault that may keep the air pump from running when needed. On Subaru specifically, this code is documented across 1 model.
What causes P0418 on Subaru vehicles?▼
Common causes on Subaru: Faulty secondary air injection relay (Relay A), Open, shorted, or corroded relay control wiring, Poor power or ground feed to the relay, Failed secondary air injection pump (drawing wrong current), Corroded relay socket or connector. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0418 on a Subaru?▼
Repair costs on Subaru range from $700 to $2,200, depending on the specific model and root cause.
Which Subaru models have P0418 documented?▼
Au7o has documented P0418 on 1 Subaru model: WRX.