What Does P1491 Mean?
The PCM has detected a circuit malfunction in the secondary air switching solenoid valve. This solenoid directs secondary air to different points in the exhaust system depending on engine conditions and emissions requirements.
Common Causes
40%
Defective secondary air switching solenoid valve
25%
Damaged wiring or short circuit in solenoid harness
20%
Corroded electrical connector terminals
10%
Vacuum leak or blockage affecting solenoid operation
5%
PCM internal driver circuit failure
Diagnostic Steps
1
Step 1: Locate secondary air switching solenoid and visually inspect for physical damage or vacuum leaks
2
Step 2: Disconnect electrical connector and test solenoid resistance with multimeter (typically 20-50 ohms)
3
Step 3: Check for battery voltage at power supply wire with key on, engine off
4
Step 4: Command solenoid activation using scan tool and verify operation (listen for click or feel for movement)
5
Step 5: Inspect vacuum lines connected to solenoid for cracks, leaks, or blockages
Estimated Repair Cost
$150 - $500
Parts + labor, varies by vehicle and location
The PCM has detected a circuit malfunction in the secondary air switching solenoid valve. This solenoid directs secondary air to different points in the exhaust system depending on engine conditions and emissions requirements.
The most common cause of P1491 (Secondary Switch Solenoid Circuit Malfunction) is: Defective secondary air switching solenoid valve
Typical repair costs for P1491 range from $150 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive with no immediate safety concerns. May result in increased cold-start emissions and potential emissions test failure.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1491 to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Powertrain
System
Emissions Control - Secondary Air Injection
Difficulty
Type
Manufacturer
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
