OBD-II Code P0491 is defined as a Secondary Air Injection System Insufficient Flow. This code is triggered when the engine control module (PCM) detects a fault with the Secondary Air Injection System, which plays a critical role in reducing emissions during the engine’s warm-up phase.
What Does the P0491 Code Mean?
The P0491 code indicates that the Secondary Air Injection System is not providing sufficient airflow. This system is designed to inject fresh air into the exhaust stream to help combust excess fuel and reduce harmful emissions during cold starts.
What Causes the P0491 Code?
Several factors can lead to the P0491 code being triggered, including:
- Clogged or disconnected vacuum hose
- Powertrain Control Module (PCM) failure
- Secondary air pump control valve failure
- Secondary air pump failure
- Wiring issues
What Are the Symptoms of the P0491 Code?
Symptoms associated with the P0491 code may include:
- Check Engine Light illumination
- Increased emissions
- Possible rough idle during cold starts
How Serious Is the P0491 Code?
The P0491 code is considered to have a moderate severity. While it may not pose an immediate threat to the vehicle’s safety or drivability, it should be diagnosed and repaired within a reasonable timeframe to ensure optimal vehicle performance and compliance with environmental regulations.
How to Diagnose the P0491 Code
To diagnose the P0491 code, a technician will typically perform the following steps:
- Use an OBD-II scanner to confirm the presence of the P0491 code.
- Inspect the Secondary Air Injection System components including the air pump, valves, and hoses for any visible damage or disconnections.
- Test the air pump operation to ensure it is functioning correctly.
- Check for any electrical issues, such as wiring problems or PCM malfunctions.
Common Repairs for the P0491 Code
Common repairs needed to address the P0491 code may include:
- Replacing the air pump
- Replacing the air pump check valve
- Repairing or replacing damaged vacuum hoses
- Fixing wiring issues
How Much Does It Cost to Fix the P0491 Code?
The cost to fix the P0491 code can vary widely depending on the nature of the issue. Minor repairs, such as replacing hoses, may cost a few hundred dollars, while more significant repairs, like replacing the air pump, can range from $500 to $1,200, including parts and labor.
Can I Fix the P0491 Code Myself?
While some aspects of diagnosing and repairing the P0491 code can be performed by a knowledgeable DIYer, such as inspecting hoses and connections, more complex issues may require professional diagnostic equipment and expertise. If you are not experienced with automotive repairs, it is recommended to consult with a certified mechanic.
