P1491 Code: Secondary Switch Solenoid Circuit Malfunction
🟠 Moderate severity · drivable
You can usually keep driving, but the emissions system won't work correctly until the solenoid circuit is fixed.
What P1491 means
The secondary switch solenoid circuit has an electrical fault. This solenoid controls airflow in the secondary air injection system, which pumps fresh air into the exhaust to help the catalytic converter warm up quickly. The engine computer detected a problem in the circuit and stored P1491.
Symptoms
- Check engine light is on
- Possible ticking or clicking from the air injection area
- Usually no driving symptoms
Common causes
- most common: Faulty secondary switch solenoid
- common: Damaged wiring or connector
- common: Blown fuse or relay
- less common: Failed air pump
How to fix it
| Fix | DIY? | Typical cost |
|---|---|---|
| Replace the secondary switch solenoid | Yes | $40–150 |
| Check and replace the fuse or relay | Yes | $10–50 |
| Inspect and repair solenoid wiring | Yes | $20–100 |
Frequently asked questions
Can I drive with a P1491 code?
Yes, usually. The engine will run, but the secondary air injection system won't work right, which can eventually affect emissions readiness tests.
What does the secondary switch solenoid do?
It controls airflow in the secondary air injection system that pushes fresh air into the exhaust to heat up the catalytic converter faster during cold starts.
How much does it cost to fix a P1491?
Most repairs cost $40–$150. The solenoid is inexpensive; the labor to reach it is often the bigger part.
Related codes
P0410
P0410 Code: Secondary Air Injection System Malfunction
P0411P0411 Code: Secondary Air Injection System Incorrect Flow Detected
P0418P0418 Code: Secondary Air Injection System Relay A Circuit Malfunction
Updated 2026-08. This page is informational and not a substitute for professional diagnosis.