P0491 - Secondary Air Injection System Insufficient Flow (Common in 2008-2012 Ford Focus, 2006-2010 Chevrolet Impala)

Quick Answer

P0491 means: P0491 indicates insufficient flow in the secondary air injection system.

Fix: Check and replace faulty components Cost: $300 - $600 Time: 90-180 minutes

Can I drive with P0491? It is advisable to diagnose and repair this issue soon to prevent further engine problems.

Common Questions

What does P0491 mean and how does it affect my car?

The P0491 code indicates that your vehicle's secondary air injection system is not functioning properly, which can lead to increased emissions and reduced engine performance. Addressing this issue is essential to ensure your vehicle runs efficiently and meets emissions standards.

What are the most common causes of P0491 and how much does it cost to fix?

Common causes include a malfunctioning secondary air pump, clogged air injection hoses, or faulty check valves. Repair costs typically range from $150 to $600, depending on the specific issue and parts needed for the fix.

Can I drive my car with P0491 or should I stop immediately?

While it may be safe to drive for a short period, it is advisable to have the P0491 code diagnosed and repaired soon. Ignoring the issue can lead to more significant engine problems and may cause your vehicle to fail emissions testing.

How can I diagnose P0491 myself using GeekOBD APP?

Using the GeekOBD APP, you can retrieve diagnostic trouble codes and freeze frame data, which provides crucial context about the issue. Follow the on-screen instructions for testing components and clearing codes after repairs.

What vehicles are most commonly affected by P0491?

Vehicles such as the 2008-2012 Ford Focus and 2006-2010 Chevrolet Impala frequently experience the P0491 code due to their secondary air injection system designs. Check for any recalls or technical service bulletins related to this code for your specific model.

How can I prevent P0491 from happening again?

Regular maintenance, including inspections of the secondary air injection system and ensuring that all components are in good working condition, can help prevent the recurrence of P0491. Additionally, using quality fuel can reduce the likelihood of carbon buildup.

What is P0491?

The P0491 diagnostic trouble code (DTC) indicates an issue with the secondary air injection system, specifically insufficient flow detected. This system is crucial for reducing vehicle emissions during cold starts, as it helps to warm up the catalytic converter more quickly. When the engine is started, the secondary air pump injects air into the exhaust system to help burn off excess fuel and reduce harmful emissions. If the PCM (Powertrain Control Module) determines that there is not enough air flow in the system, it triggers the P0491 code. Common symptoms include the check engine light illuminating, reduced engine performance, and potentially decreased fuel efficiency. Ignoring this code could lead to further complications, such as damage to the catalytic converter or increased emissions, which can cause the vehicle to fail emissions tests. Vehicle owners should address this issue promptly to maintain optimal performance and compliance with environmental regulations.

System: P - Powertrain (Engine, Transmission, Emissions)

Symptoms

Common symptoms when P0491 is present:

  • The check engine light comes on and remains illuminated, indicating a problem with the vehicle's emissions system.
  • Drivers may notice a decrease in engine performance, with sluggish acceleration or difficulty maintaining speed, especially during cold starts.
  • Fuel economy could decrease by about 10-15%, as the vehicle's engine struggles to operate efficiently without the proper air flow.
  • Unusual engine noises, such as a whining sound from the secondary air pump, may be heard when the pump is activated during startup.
  • In some cases, there may be a noticeable increase in exhaust emissions, leading to potential issues during emissions testing.

Possible Causes

Most common causes of P0491 (ordered by frequency):

  1. The most common cause of P0491 is a malfunctioning secondary air pump, which has about a 55% likelihood of being the issue. This pump can fail due to wear and tear or electrical issues.
  2. A clogged or damaged air injection hose can also lead to insufficient air flow, accounting for approximately 25% of cases. This can happen due to debris buildup or physical damage.
  3. Another cause is a faulty check valve, preventing proper air flow into the exhaust system. Regular inspections can help prevent this issue by ensuring all components are functioning correctly.
  4. Less common but serious causes include problems with the PCM itself, which may not be sending the correct signals to the secondary air system.
  5. Rarely, a restriction in the exhaust system, such as a clogged catalytic converter, can cause this code to appear due to improper exhaust flow.

P0491 Repair Costs

Cost Breakdown by Repair Type

Secondary Air Pump Replacement

Replacing a faulty secondary air pump to restore proper air flow in the system.

  • Total: $300 - $600
  • Success rate: 90%
Check Valve Replacement

Replaced faulty check valve to ensure proper air flow into the exhaust system.

  • Total: $150 - $300
  • Success rate: 80%
Money-Saving Tips for P0491
  • Start with the most common and least expensive repairs first
  • Use GeekOBD APP to confirm diagnosis before replacing expensive parts
  • Consider preventive maintenance to avoid future occurrences
  • Compare prices for OEM vs aftermarket parts based on your needs
  • Address the issue promptly to prevent more expensive secondary damage

Diagnostic Steps

Professional P0491 Diagnosis Process

Follow these systematic steps to accurately diagnose P0491. Each step builds on the previous one to ensure accurate diagnosis.

Step 1: Step 1: Initial visual inspection - Check for obvious signs like damaged wiring, loose connections, or corrosion in the secondary air system components (5-10 minutes)

Step 1: Initial visual inspection - Check for obvious signs like damaged wiring, loose connections, or corrosion in the secondary air system components (5-10 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 2: Step 2: OBD2 scan with GeekOBD APP - Retrieve all codes and freeze frame data to understand the fault context (10-15 minutes)

Step 2: OBD2 scan with GeekOBD APP - Retrieve all codes and freeze frame data to understand the fault context (10-15 minutes). This app can help identify related trouble codes that may provide further insight.

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 3: Step 3: Component testing - Use a multimeter or specific diagnostic tools to test the secondary air pump and check valves for proper function (20-30 minutes)

Step 3: Component testing - Use a multimeter or specific diagnostic tools to test the secondary air pump and check valves for proper function (20-30 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 4: Step 4: System function test - Verify proper operation after any repairs and clear codes using the GeekOBD APP to reset the vehicle's systems (10-15 minutes)

Step 4: System function test - Verify proper operation after any repairs and clear codes using the GeekOBD APP to reset the vehicle's systems (10-15 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 5: Step 5: Road test verification - Drive the vehicle under various conditions to confirm repair success and ensure the check engine light does not return (15-20 minutes)

Step 5: Road test verification - Drive the vehicle under various conditions to confirm repair success and ensure the check engine light does not return (15-20 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.

Important Notes

  • Always verify the repair with GeekOBD APP after completing diagnostic steps
  • Clear codes and test drive to ensure the problem is resolved
  • Address underlying causes to prevent code recurrence

Real Repair Case Studies

Case Study 1: Ford Focus Secondary Air Pump Replacement

Vehicle: 2010 Ford Focus, 85,000 miles

Problem: Customer reported check engine light and reduced acceleration during cold starts.

Diagnosis: After scanning with the GeekOBD APP, P0491 was confirmed. A visual inspection revealed a failed secondary air pump.

Solution: Replaced the secondary air pump and air injection hose, cleared the codes, and performed a road test.

Cost: $450 (parts: $250 for the pump, $50 for the hose, $150 labor)

Result: The repair resolved the check engine light issue, and the vehicle's performance improved significantly.

Case Study 2: Chevrolet Impala Check Valve Replacement

Vehicle: 2008 Chevrolet Impala, 90,000 miles

Problem: Customer experienced poor fuel economy and check engine light activation.

Diagnosis: P0491 was confirmed via the GeekOBD APP; testing indicated a faulty check valve.

Solution: Replaced the check valve and performed a system function test to ensure proper operation.

Cost: $200 (parts: $100 for the check valve, $100 labor)

Result: Post-repair, the vehicle showed improved fuel economy and the check engine light remained off.

Diagnose P0491

Use GeekOBD APP for professional diagnosis!

  • Real-time data monitoring
  • Advanced diagnostic features
  • Step-by-step repair guidance
  • Professional-grade analysis
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Code Information

Code: P0491
System: Powertrain (Engine, Transmission, Emissions)
Severity: MEDIUM
Category: Engine Codes