P0418
Secondary Air Injection System Relay "A" Circuit Malfunction
General electrical fault in the secondary air injection pump relay A circuit. Without the relay, the air pump cannot be commanded and the system cannot complete its cold-start function.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: easy
Common causes
Ordered by how often each turns out to be the cause.
- Air pump relay failedCommon
- Wiring or connector faultPossible
Parts involved
- Secondary Air Relay
- Secondary Air Pump
- Relay Wiring
P0418 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.