Secondary Air Injection Relay A Circuit Malfunction
The P0418 code indicates a malfunction in the electrical circuit of relay 'A' for the secondary air injection system. This system pumps fresh air into the exhaust manifold during cold starts to reduce emissions. The relay controls power to the air pump; a circuit fault can prevent the pump from operating, leading to increased emissions and potential check engine light illumination.
01. Most Common Causes
- Faulty secondary air injection relay
- Blown fuse or wiring issues (open/short)
- Corroded or loose relay connector
- Failed engine control module (rare)
02. Symptoms You Will Notice
- Check engine light on
- Failed emissions test
- Rough idle or hesitation on cold start
- Possible reduced fuel economy
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm P0418 and check for related codes.
Step 2: Inspect the secondary air injection relay and its fuse; test relay operation with a multimeter.
Step 3: Check wiring and connector for damage, corrosion, or loose connections.
Step 4: If relay and wiring are good, test the air pump and control circuit; replace relay if faulty.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
Yes, but the vehicle may fail an emissions test and the check engine light will stay on. It's best to repair promptly to avoid potential driveability issues.
How much does it cost to fix?▼
Typically $50-$150 for parts and labor, depending on whether it's a relay, fuse, or wiring repair.