Secondary Air Injection System Relay "A" Circuit Malfunction
The Secondary Air Injection (SAI) pump relay circuit is not functioning properly, preventing the air injection system from activating during cold starts and warm-up cycles. This system reduces emissions but is not critical to engine operation, though the vehicle will fail emissions testing if the fault persists.
What You Might Notice
- Check Engine Light illuminated
- No SAI pump activation or noise during cold start
- Vehicle may fail emissions inspection
- Possible increased exhaust emissions
- No noticeable drivability issues in most cases
Most Common Causes
- 1
Defective SAI pump relay
The relay that controls power to the SAI pump has failed internally or has poor electrical contact. This is the most common cause of P0418.
- 2
Blown SAI system fuse
The dedicated fuse protecting the SAI pump circuit has blown due to an electrical fault or component failure, cutting power to the relay.
- 3
Shorted or damaged wiring in SAI circuit
Corroded, pinched, or damaged wires and connectors in the SAI system circuit prevent proper voltage delivery to the relay.
- 4
Defective SAI pump
The secondary air injection pump itself has failed electrically, creating a short or load that burns out the relay or blows the fuse repeatedly.
How to Diagnose It
- 1
Check Defective SAI pump relay — The relay that controls power to the SAI pump has failed internally or has poor electrical contact. This is the most common cause of P0418.
- 2
Check Blown SAI system fuse — The dedicated fuse protecting the SAI pump circuit has blown due to an electrical fault or component failure, cutting power to the relay.
- 3
Check Shorted or damaged wiring in SAI circuit — Corroded, pinched, or damaged wires and connectors in the SAI system circuit prevent proper voltage delivery to the relay.
- 4
Check Defective SAI pump — The secondary air injection pump itself has failed electrically, creating a short or load that burns out the relay or blows the fuse repeatedly.
How to Fix It
- 1
Replace SAI pump relay
Locate the relay in the engine bay fuse/relay panel, remove it, and install a new relay of the correct specification for your vehicle model.
- 2
Replace blown SAI system fuse
Check the fuse panel for the SAI fuse, test it for continuity, and replace with a new fuse of the correct amperage if blown. Do not replace with a higher-rated fuse.
- 3
Inspect and repair SAI wiring and connectors
Trace the SAI circuit from the relay to the pump, checking for corroded, loose, or damaged connectors. Clean contacts, repair or replace damaged wiring as needed.
- 4
Replace SAI pump
If the pump is shorted or faulty and continues to blow fuses after relay replacement, remove the defective pump and install a new secondary air injection pump assembly.
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