P0418
PowertrainSecondary Airlow severitySecondary Air Injection System Relay A Circuit Malfunction
What P0418 Means
The PCM detected a fault in the secondary air injection pump relay A circuit. This relay powers the air pump used to reduce cold-start emissions.
Symptoms
- Check engine light on
- Air pump not running
- Failed emissions test
Common Causes
- Faulty air pump relay
- Open or shorted relay wiring
- Blown fuse
- Faulty PCM driver
Diagnostic Steps
- Scan and confirm P0418
- Test relay operation
- Check relay wiring and fuse
- Verify PCM control signal
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