P0491
PowertrainSecondary Air Systemlow severitySecondary Air Injection System Insufficient Flow Bank 1
What P0491 Means
The PCM has detected insufficient secondary air flow on bank 1. This reduces the system's ability to lower emissions during cold starts.
Symptoms
- Check engine light on
- Failed emissions test
- Rough cold-start running
Common Causes
- Faulty secondary air pump
- Clogged air passages
- Stuck air injection valve
- Damaged wiring or hoses
Diagnostic Steps
- Scan for stored codes
- Test secondary air pump operation
- Inspect air injection valves and hoses
- Check for clogged passages
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