Secondary Air Injection System Relay A Circuit Malfunction
What does P0418 mean?
The P0418 code means the vehicle's onboard diagnostic system has detected: Secondary Air Injection System Relay A Circuit Malfunction. This is a low severity code.
Common Symptoms
- Check Engine Light illuminated
- Air pump does not activate on cold start
- No drivability issues
- Failed emissions test
Probable Causes (Ranked by Likelihood)
- Failed secondary air pump relay Very High
- Open or shorted relay control circuit wiring High
- Corroded relay socket in fuse box Moderate
- ECM relay driver circuit fault Low
Step-by-Step Diagnostic Procedure
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Locate the secondary air pump relay in the fuse box and swap it with a known-good relay of the same type
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Check for power and ground at the relay socket with the key on
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Verify the ECM is commanding the relay on during cold start using a scan tool
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Inspect relay socket terminals for corrosion or heat damage
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Check relay control circuit wiring from ECM to the relay socket
Frequently Asked Questions
Can I drive with code P0418?
Yes. The relay controls the air pump which only runs during cold starts. Normal driving and engine performance are not affected.
How do I test the secondary air relay?
Swap it with another relay of the same type from the fuse box (such as the horn relay). If the air pump works with the swapped relay, the original relay has failed.
Is the relay an easy fix?
Yes. The relay is a plug-in component in the fuse box, typically costing $15-$40. It is one of the easiest repairs in the secondary air system.