E39 OBD2 Codes 0491: Comprehensive Guide to Troubleshooting

OBD2 code 0491 on an E39 BMW signals an issue with the secondary air injection system. At OBD2-SCANNER.EDU.VN, we help you understand why this code appears, how to diagnose it correctly, and what steps to take for effective repairs, ensuring your BMW runs smoothly. Learn about secondary air injection faults, diagnose air pump problems, and find solutions.

1. What Does the E39 OBD2 Code 0491 Mean?

The E39 OBD2 code 0491, typically found in BMWs, indicates “Secondary Air Injection System Insufficient Flow Bank 1.” This means the Engine Control Unit (ECU) has detected that the secondary air injection system is not functioning correctly on engine bank 1. The purpose of this system is to pump fresh air into the exhaust system during cold starts to help burn off excess hydrocarbons, reducing emissions. When the ECU detects insufficient airflow, it triggers the code, potentially affecting your vehicle’s emissions and performance. Understanding the specifics of this system is critical to diagnosing and fixing the problem efficiently.

• Secondary Air Injection System: This system pumps air into the exhaust stream during cold starts to reduce emissions.
• Insufficient Flow: The ECU detects that not enough air is being injected into the exhaust system.
• Bank 1: Refers to the side of the engine containing cylinder number 1.

This image shows the engine bay of a BMW E39, where the secondary air injection system components are located.

2. What are the Common Causes of OBD2 Code 0491 in an E39?

Several issues can trigger the OBD2 code 0491 in your BMW E39. Identifying these common causes can help streamline the diagnostic process and lead to quicker, more effective repairs.

• Failed Secondary Air Pump: The air pump might be defective and unable to pump air into the exhaust system.
• Faulty Check Valve: A malfunctioning check valve can prevent air from flowing correctly or allow exhaust gases to flow back into the pump, damaging it.
• Clogged Air Injection Passages: Carbon buildup can block the passages that deliver air to the exhaust ports.
• Vacuum Leaks: Leaks in the vacuum lines controlling the secondary air system can disrupt its operation.
• Defective Vacuum Switch: A faulty vacuum switch may fail to properly control the air injection system.
• Faulty Oxygen Sensors: Although less common, malfunctioning oxygen sensors can sometimes trigger this code by providing incorrect readings to the ECU.
• Wiring or Connector Issues: Damaged or corroded wiring and connectors can interrupt the electrical signals needed for the system to function.

3. What are the Symptoms of OBD2 Code 0491?

Recognizing the symptoms associated with the OBD2 code 0491 can help you identify the problem early and prevent further damage. While some symptoms are immediately noticeable, others might require closer inspection.

• Check Engine Light: The most obvious symptom is the illumination of the check engine light on your dashboard.
• Failed Emissions Test: The vehicle may fail an emissions test due to the increased levels of hydrocarbons released during cold starts.
• Rough Idle During Cold Start: You might notice a rough or unstable idle when starting the engine cold.
• Decreased Fuel Economy: Although not always significant, some drivers report a slight decrease in fuel economy.
• Unusual Noises: Strange sounds from the secondary air pump area, such as whining or grinding, can indicate a failing pump.

4. How to Diagnose the E39 OBD2 Code 0491: A Step-by-Step Guide

Diagnosing the E39 OBD2 code 0491 requires a systematic approach to pinpoint the exact cause of the problem. This step-by-step guide will help you through the process, ensuring accurate and effective troubleshooting.

1. Read the OBD2 Code:

   • Use an OBD2 scanner to confirm the presence of code 0491.
   • Note any other related codes that may be present.

2. Inspect the Secondary Air Pump:

   • Visually inspect the pump for any signs of damage or corrosion.
   • Check the electrical connections to ensure they are secure.

3. Test the Air Pump Operation:

   • Start the engine cold and listen for the air pump running. It usually runs for about 60-90 seconds.
   • If the pump doesn’t run, check the fuse and relay associated with the air pump.

4. Check the Check Valve:

   • Locate the check valve in the secondary air injection system.
   • Inspect it for any signs of corrosion or damage.
   • Test the valve to ensure it allows air to flow in only one direction.

5. Inspect Vacuum Lines:

   • Check all vacuum lines connected to the secondary air system for cracks, leaks, or disconnections.
   • Replace any damaged or suspect lines.

6. Check Air Injection Passages:

   • Inspect the air injection passages for carbon buildup.
   • Use a small brush or pipe cleaner to remove any obstructions.

7. Monitor Oxygen Sensor Readings:

   • Use the OBD2 scanner to monitor the oxygen sensor readings during a cold start.
   • Look for delayed or abnormal readings that may indicate a sensor issue.

8. Perform a Smoke Test:

   • Conduct a smoke test on the intake and exhaust systems to identify any vacuum leaks.
   • Address any leaks found to ensure proper system operation.

9. Clear the Code and Retest:

   • After completing the inspections and repairs, clear the OBD2 code using the scanner.
   • Start the engine and allow it to run to see if the code returns.

An OBD2 scanner displaying error codes can help pinpoint the source of the issue.

5. How to Fix the E39 OBD2 Code 0491: Solutions and Repairs

Once you have diagnosed the cause of the OBD2 code 0491, implementing the right repairs is essential. Here are some solutions to address the common issues associated with this code.

1. Replace the Secondary Air Pump:

   • If the air pump is defective, replace it with a new or refurbished unit.
   • Ensure the replacement pump is compatible with your E39 model.

2. Replace the Check Valve:

   • A faulty check valve should be replaced to ensure proper airflow and prevent exhaust backflow.
   • Choose a high-quality replacement valve to ensure longevity.

3. Clean Air Injection Passages:

   • Remove any carbon buildup from the air injection passages using a brush or solvent.
   • Ensure the passages are clear to allow unrestricted airflow.

4. Repair or Replace Vacuum Lines:

   • Repair any leaks in the vacuum lines with appropriate connectors or replace the lines entirely.
   • Use high-quality vacuum lines to prevent future issues.

5. Replace the Vacuum Switch:

   • If the vacuum switch is faulty, replace it to ensure proper control of the air injection system.
   • Test the new switch to verify its functionality.

6. Replace Oxygen Sensors:

   • If the oxygen sensors are providing incorrect readings, replace them with new sensors.
   • Ensure the replacement sensors are compatible with your vehicle.

7. Repair Wiring and Connectors:

   • Repair any damaged or corroded wiring and connectors in the secondary air system.
   • Use dielectric grease to protect the connections from future corrosion.

8. Update the ECU Software:

   • In some cases, an outdated ECU software version can cause false error codes.
   • Update the ECU software to the latest version to resolve this issue.

6. What are the Parts Needed to Fix OBD2 Code 0491 on an E39?

Having a list of the necessary parts can streamline the repair process. Here’s a breakdown of the parts commonly needed to fix the OBD2 code 0491 on your BMW E39.

• Secondary Air Pump: The primary component for injecting air into the exhaust system.
• Check Valve: Prevents backflow of exhaust gases into the air pump.
• Vacuum Lines: Connect various components of the secondary air system.
• Vacuum Switch: Controls the flow of vacuum to the system components.
• Oxygen Sensors: Monitor the exhaust gases and provide feedback to the ECU.
• Fuses and Relays: Protect and control the electrical components of the system.
• Wiring and Connectors: Ensure proper electrical connections.
• Air Injection Hoses: Deliver air from the pump to the exhaust manifold.

7. Estimated Cost to Repair OBD2 Code 0491 on an E39

Understanding the potential costs associated with repairing OBD2 code 0491 can help you budget effectively. Here’s a cost breakdown for common repairs:

• Secondary Air Pump Replacement: $200 – $500 (including parts and labor)
• Check Valve Replacement: $50 – $150 (including parts and labor)
• Vacuum Line Repair/Replacement: $30 – $100 (including parts and labor)
• Vacuum Switch Replacement: $80 – $200 (including parts and labor)
• Oxygen Sensor Replacement: $100 – $300 (including parts and labor per sensor)
• Air Injection Passage Cleaning: $50 – $150 (labor cost)
• Wiring/Connector Repair: $50 – $200 (labor cost, depending on complexity)

These costs can vary depending on your location, the specific repair shop, and the quality of the parts used. Getting multiple quotes can help ensure you receive a fair price.

8. How to Prevent OBD2 Code 0491 from Recurring

Preventing the recurrence of OBD2 code 0491 involves regular maintenance and proactive care of your vehicle’s secondary air injection system. Here are some tips to help keep this code at bay:

• Regular Inspections: Periodically inspect the components of the secondary air system, including the pump, check valve, and vacuum lines.
• Timely Maintenance: Follow the manufacturer’s recommended maintenance schedule for your BMW E39.
• Use Quality Parts: When replacing components, opt for high-quality parts that meet or exceed OEM specifications.
• Check for Vacuum Leaks: Regularly check for vacuum leaks and address them promptly.
• Keep Air Injection Passages Clean: Periodically clean the air injection passages to prevent carbon buildup.
• Monitor Oxygen Sensor Performance: Keep an eye on your oxygen sensor readings and replace them as needed.
• Avoid Short Trips: Whenever possible, avoid frequent short trips, as these can contribute to carbon buildup and system inefficiency.

9. Can I Drive My E39 with OBD2 Code 0491?

While it is technically possible to drive your E39 with OBD2 code 0491, it is not recommended for extended periods. Driving with this code can lead to several potential issues:

• Increased Emissions: The secondary air injection system is designed to reduce emissions during cold starts. Driving with a malfunctioning system can increase harmful emissions.
• Failed Emissions Test: Your vehicle may fail an emissions test, preventing you from legally operating it.
• Potential Damage to Components: A malfunctioning secondary air system can cause other components to work harder, potentially leading to premature failure.
• Reduced Fuel Economy: Although not always significant, you may experience a slight decrease in fuel economy.

Addressing the issue promptly is the best course of action to avoid these potential problems.

10. Understanding the Role of Oxygen Sensors in the E39’s Secondary Air Injection System

Oxygen sensors play a crucial role in the overall operation of the E39’s secondary air injection system. These sensors monitor the amount of oxygen in the exhaust gases, providing feedback to the ECU. This information helps the ECU adjust the air-fuel mixture and ensure efficient combustion. In the context of the secondary air injection system, oxygen sensors help the ECU determine if the system is functioning correctly.

• Monitoring Exhaust Gases: Oxygen sensors continuously monitor the levels of oxygen in the exhaust gases.
• Feedback to the ECU: They provide real-time data to the ECU, which uses this information to make adjustments.
• Ensuring Efficient Combustion: By monitoring oxygen levels, the sensors help ensure that the engine is burning fuel efficiently.
• Detecting System Malfunctions: If the oxygen sensors detect abnormal readings, it can indicate a problem with the secondary air injection system, triggering the OBD2 code 0491.

An oxygen sensor monitors the exhaust gases to ensure efficient combustion.

11. The Impact of Carbon Buildup on the E39’s Air Injection Passages

Carbon buildup in the air injection passages is a common issue that can lead to the OBD2 code 0491. Over time, carbon deposits can accumulate in these passages, restricting the flow of air and reducing the efficiency of the secondary air injection system.

• Restricted Airflow: Carbon buildup narrows the air injection passages, reducing the amount of air that can reach the exhaust system.
• Reduced System Efficiency: The reduced airflow decreases the effectiveness of the secondary air injection system, leading to increased emissions.
• Potential Overheating: Restricted airflow can cause the air pump to work harder, potentially leading to overheating and premature failure.
• Triggering the OBD2 Code: The ECU detects the reduced airflow and triggers the OBD2 code 0491.

Regularly cleaning the air injection passages can help prevent carbon buildup and ensure the proper operation of the secondary air injection system.

12. How Vacuum Leaks Affect the E39’s Secondary Air Injection System

Vacuum leaks can significantly impact the performance of the E39’s secondary air injection system. The system relies on vacuum to control various components, such as the vacuum switch and check valve. Leaks in the vacuum lines can disrupt the system’s operation, leading to reduced efficiency and the triggering of the OBD2 code 0491.

• Disrupted System Operation: Vacuum leaks interfere with the proper functioning of the vacuum-controlled components.
• Reduced Efficiency: The reduced vacuum pressure can decrease the effectiveness of the secondary air injection system.
• Incorrect Valve Operation: Vacuum leaks can prevent the check valve and vacuum switch from operating correctly.
• Triggering the OBD2 Code: The ECU detects the abnormal system behavior and triggers the OBD2 code 0491.

Performing a smoke test can help identify vacuum leaks, allowing you to address them promptly and restore the system’s proper operation.

13. The Role of the Check Valve in Preventing Exhaust Backflow

The check valve is a critical component of the E39’s secondary air injection system, designed to prevent exhaust gases from flowing back into the air pump. This valve allows air to flow in only one direction, ensuring that the air pump is protected from damaging exhaust gases.

• Preventing Backflow: The check valve prevents exhaust gases from flowing back into the air pump.
• Protecting the Air Pump: By preventing backflow, the check valve helps protect the air pump from corrosion and damage.
• Ensuring Proper Airflow: The valve ensures that air flows in the correct direction, maximizing the efficiency of the secondary air injection system.
• Maintaining System Integrity: A properly functioning check valve is essential for maintaining the overall integrity of the secondary air injection system.

A faulty check valve can allow exhaust gases to damage the air pump, leading to costly repairs.

14. How to Test the Secondary Air Pump on an E39

Testing the secondary air pump is an essential step in diagnosing the OBD2 code 0491. Here’s how to test the air pump to ensure it is functioning correctly:

1. Visual Inspection:

   • Inspect the air pump for any signs of physical damage or corrosion.
   • Check the electrical connections to ensure they are secure.

2. Listening for Operation:

   • Start the engine cold and listen for the air pump running. It typically runs for about 60-90 seconds.
   • If you don’t hear the pump, proceed to the next steps.

3. Checking the Fuse and Relay:

   • Locate the fuse and relay associated with the air pump in the fuse box.
   • Check the fuse for continuity using a multimeter.
   • Test the relay to ensure it is functioning correctly.
   • Replace any blown fuses or faulty relays.

4. Testing Voltage to the Pump:

   • Use a multimeter to check for voltage at the air pump connector when the engine is started cold.
   • You should see approximately 12 volts.
   • If there is no voltage, there may be a wiring issue.

5. Directly Powering the Pump:

   • Disconnect the air pump from the vehicle’s electrical system.
   • Apply 12 volts directly to the pump using jumper cables.
   • If the pump runs, the issue is likely in the vehicle’s wiring or control system.
   • If the pump doesn’t run, it is likely defective and needs to be replaced.

By following these steps, you can effectively test the secondary air pump and determine if it is the cause of the OBD2 code 0491.

15. What is the Expected Lifespan of the Secondary Air Pump on an E39?

The lifespan of the secondary air pump on an E39 can vary depending on several factors, including the quality of the pump, driving conditions, and maintenance practices. Generally, you can expect the secondary air pump to last between 80,000 to 120,000 miles.

• Quality of the Pump: High-quality pumps from reputable manufacturers tend to last longer.
• Driving Conditions: Frequent short trips can shorten the pump’s lifespan due to increased wear and tear.
• Maintenance Practices: Regular inspections and timely repairs can help extend the pump’s lifespan.
• Environmental Factors: Exposure to harsh weather conditions and road debris can also affect the pump’s lifespan.

Monitoring the pump’s performance and addressing any issues promptly can help ensure it lasts as long as possible.

16. How to Clear the OBD2 Code 0491 After Repairing the Issue

After addressing the underlying cause of the OBD2 code 0491, it is essential to clear the code from the vehicle’s computer. Here’s how to clear the code using an OBD2 scanner:

1. Connect the OBD2 Scanner:

   • Plug the OBD2 scanner into the diagnostic port, typically located under the dashboard on the driver’s side.

2. Turn On the Ignition:

   • Turn the ignition key to the “on” position without starting the engine.

3. Navigate to the Code Clearing Function:

   • Use the scanner’s menu to navigate to the “Clear Codes” or “Erase Codes” function.

4. Confirm the Code Clearing:

   • Follow the scanner’s prompts to confirm that you want to clear the codes.

5. Verify the Code is Cleared:

   • After clearing the codes, turn off the ignition and then turn it back on.
   • Use the scanner to read the codes again and verify that the OBD2 code 0491 is no longer present.

6. Test Drive the Vehicle:

   • Take the vehicle for a test drive to ensure that the code does not return.

If the code returns, it indicates that there is still an underlying issue that needs to be addressed.

17. The Connection Between Faulty Oxygen Sensors and OBD2 Code 0491

Faulty oxygen sensors can sometimes be linked to the OBD2 code 0491, although it is less common. Oxygen sensors monitor the amount of oxygen in the exhaust gases and provide feedback to the ECU. If these sensors are malfunctioning, they can provide incorrect readings, leading the ECU to misinterpret the performance of the secondary air injection system.

• Incorrect Readings: Faulty oxygen sensors can provide inaccurate data to the ECU.
• Misinterpretation of System Performance: The ECU may misinterpret the data and incorrectly assume that the secondary air injection system is not functioning correctly.
• Triggering the OBD2 Code: The ECU may trigger the OBD2 code 0491 based on the incorrect sensor readings.
• Impact on Air-Fuel Mixture: Faulty oxygen sensors can also affect the air-fuel mixture, which can indirectly impact the secondary air injection system.

If you suspect that faulty oxygen sensors are contributing to the OBD2 code 0491, it is essential to test and replace them as needed.

18. How Does the E39’s DME (Digital Motor Electronics) Control the Secondary Air Injection System?

The E39’s DME (Digital Motor Electronics), also known as the ECU (Engine Control Unit), plays a central role in controlling the secondary air injection system. The DME monitors various parameters, such as engine temperature, oxygen sensor readings, and vacuum levels, to determine when and how to activate the system.

• Monitoring System Parameters: The DME monitors various sensors to gather data about the engine’s operating conditions.
• Activating the System: Based on the sensor data, the DME activates the secondary air injection system during cold starts.
• Controlling System Components: The DME controls the air pump, vacuum switch, and other components to ensure proper system operation.
• Detecting Malfunctions: The DME monitors the system’s performance and detects any malfunctions, triggering the OBD2 code 0491 when necessary.

Understanding how the DME controls the secondary air injection system can help you troubleshoot issues more effectively.

19. The Importance of Using OEM Parts When Repairing the E39’s Secondary Air Injection System

When repairing the E39’s secondary air injection system, using OEM (Original Equipment Manufacturer) parts is highly recommended. OEM parts are designed and manufactured to meet the exact specifications of your vehicle, ensuring proper fit, performance, and reliability.

• Proper Fit: OEM parts are designed to fit perfectly in your vehicle, avoiding any installation issues.
• Optimal Performance: OEM parts are engineered to deliver the same level of performance as the original components.
• Reliability: OEM parts are made from high-quality materials and are designed to last, reducing the risk of premature failure.
• Compatibility: OEM parts are guaranteed to be compatible with your vehicle’s systems, avoiding any potential conflicts or issues.

While aftermarket parts may be less expensive, they may not offer the same level of quality and reliability as OEM parts.

20. Tips for Maintaining Vacuum Lines to Prevent OBD2 Code 0491

Maintaining the vacuum lines in your E39’s secondary air injection system is crucial for preventing the OBD2 code 0491. Here are some tips to help keep your vacuum lines in good condition:

• Regular Inspections: Periodically inspect the vacuum lines for any signs of cracks, leaks, or damage.
• Proper Routing: Ensure that the vacuum lines are properly routed and secured to prevent them from rubbing against other components.
• Use High-Quality Lines: Replace any damaged or suspect vacuum lines with high-quality replacements.
• Avoid Harsh Chemicals: Avoid using harsh chemicals or solvents near the vacuum lines, as these can cause them to deteriorate.
• Check Connections: Ensure that all connections are secure and free from corrosion.
• Replace Aged Lines: Even if the vacuum lines appear to be in good condition, consider replacing them after a certain period (e.g., every 5-7 years) to prevent future issues.

By following these tips, you can help maintain the vacuum lines and prevent vacuum leaks that can lead to the OBD2 code 0491.

21. Step-by-Step Guide to Cleaning the Air Injection Passages on an E39

Cleaning the air injection passages is an essential maintenance task for preventing OBD2 code 0491. Here’s a step-by-step guide to help you through the process:

1. Gather Your Supplies:

   • Safety glasses
   • Gloves
   • Small wire brush
   • Carburetor cleaner or intake cleaner
   • Socket set
   • Wrench set

2. Locate the Air Injection Passages:

   • Consult your vehicle’s repair manual to identify the location of the air injection passages. These are typically found on the cylinder head near the exhaust ports.

3. Remove Any Obstructions:

   • Use a socket or wrench to remove any components that may be blocking access to the air injection passages.

4. Apply Carburetor Cleaner:

   • Spray carburetor cleaner or intake cleaner into the air injection passages.
   • Allow the cleaner to soak for several minutes to loosen any carbon deposits.

5. Scrub the Passages:

   • Use a small wire brush to scrub the air injection passages and remove any remaining carbon deposits.

6. Rinse the Passages:

   • Spray more carburetor cleaner or intake cleaner into the passages to rinse away any loose debris.

7. Reassemble Components:

   • Reassemble any components that were removed to access the air injection passages.

8. Test the System:

   • Start the engine and listen for the air pump to ensure that it is functioning correctly.
   • Clear the OBD2 code 0491 using an OBD2 scanner.

By following these steps, you can effectively clean the air injection passages and prevent carbon buildup that can lead to the OBD2 code 0491.

22. How to Check the Check Valve on an E39’s Secondary Air Injection System

The check valve is a crucial component of the secondary air injection system, preventing exhaust gases from flowing back into the air pump. Here’s how to check the check valve to ensure it’s functioning correctly:

1. Locate the Check Valve:

   • The check valve is typically located in the air line between the secondary air pump and the exhaust manifold.
   • Consult your vehicle’s repair manual for the exact location.

2. Visual Inspection:

   • Inspect the check valve for any signs of physical damage, corrosion, or cracks.

3. One-Way Airflow Test:

   • Disconnect the air line from both sides of the check valve.
   • Try blowing air through the valve in one direction. It should allow airflow.
   • Try blowing air through the valve in the opposite direction. It should block airflow.
   • If the valve allows airflow in both directions or blocks airflow in both directions, it is faulty and needs to be replaced.

4. Vacuum Test (if applicable):

   • Some check valves are vacuum-operated. If your check valve has a vacuum line, inspect it for any signs of damage or leaks.
   • Use a vacuum pump to apply vacuum to the valve and ensure that it opens and closes properly.

If the check valve fails any of these tests, it should be replaced to ensure the proper operation of the secondary air injection system.

23. How to Inspect the Wiring and Connectors in the E39’s Secondary Air Injection System

Inspecting the wiring and connectors in the secondary air injection system is vital for diagnosing and preventing the OBD2 code 0491. Follow these steps to ensure the electrical components are in good condition:

1. Gather Your Supplies:

   • Multimeter
   • Flashlight
   • Wire brush
   • Electrical contact cleaner
   • Wiring diagram for your E39 model

2. Locate the Wiring and Connectors:

   • Consult your vehicle’s wiring diagram to identify the wiring and connectors associated with the secondary air injection system.
   • Pay close attention to the wiring near the air pump, check valve, vacuum switch, and oxygen sensors.

3. Visual Inspection:

   • Inspect the wiring for any signs of damage, such as cuts, fraying, or melted insulation.
   • Inspect the connectors for any signs of corrosion, dirt, or damage.

4. Continuity Test:

   • Use a multimeter to perform a continuity test on the wiring.
   • Disconnect the battery before performing this test.
   • Check for continuity between the various components of the secondary air injection system.
   • If there is no continuity, there may be a break in the wiring that needs to be repaired.

5. Voltage Test:

   • Use a multimeter to check for voltage at the connectors when the engine is running.
   • Consult your vehicle’s wiring diagram for the correct voltage readings.
   • If there is no voltage, there may be a problem with the power supply to the system.

6. Clean the Connectors:

   • Use a wire brush and electrical contact cleaner to clean any corroded or dirty connectors.
   • Apply dielectric grease to the connectors to protect them from future corrosion.

7. Repair or Replace Damaged Wiring and Connectors:

   • Repair any damaged wiring using appropriate connectors and splices.
   • Replace any connectors that are severely corroded or damaged.

By following these steps, you can thoroughly inspect the wiring and connectors in the secondary air injection system and address any issues that may be contributing to the OBD2 code 0491.

24. Updating the ECU Software to Resolve False OBD2 Code 0491 Errors

In some cases, an outdated ECU (Engine Control Unit) software version can cause false OBD2 code 0491 errors. Updating the ECU software to the latest version can sometimes resolve this issue. Here’s how to proceed:

1. Check Your Current Software Version:

   • Consult your vehicle’s repair manual or a qualified technician to determine the current software version of your ECU.

2. Determine if an Update is Available:

   • Contact your local BMW dealer or a trusted mechanic to inquire about any available software updates for your vehicle.

3. Schedule an ECU Update:

   • If an update is available, schedule an appointment with the dealer or mechanic to have the ECU software updated.

4. Ensure Proper Installation:

   • Make sure the update is installed correctly to avoid any potential issues.

5. Clear the OBD2 Code:

   • After the update is complete, clear the OBD2 code 0491 using an OBD2 scanner.

6. Test Drive the Vehicle:

   • Take the vehicle for a test drive to ensure that the code does not return.

Updating the ECU software can be a simple and effective way to resolve false OBD2 code 0491 errors and improve your vehicle’s overall performance.

25. OBD2 Code 0491 and Its Impact on Vehicle Emissions

The OBD2 code 0491 directly relates to the vehicle’s emissions. The secondary air injection system is designed to reduce harmful emissions during cold starts. When this system malfunctions, it can lead to:

• Increased Hydrocarbon Emissions: The secondary air injection system helps burn off excess hydrocarbons during cold starts. A malfunctioning system can result in higher levels of hydrocarbon emissions.
• Failed Emissions Test: Vehicles with a malfunctioning secondary air injection system are likely to fail emissions tests, preventing them from being legally operated.
• Environmental Impact: Increased emissions contribute to air pollution and can have a negative impact on the environment.

Addressing the OBD2 code 0491 promptly is essential for reducing emissions and maintaining compliance with environmental regulations.

26. How to Determine if You Need to Replace or Clean the Air Injection Passages

Deciding whether to replace or clean the air injection passages depends on the extent of the carbon buildup and the overall condition of the passages. Here’s how to determine the best course of action:

1. Visual Inspection:

   • Inspect the air injection passages for carbon buildup.
   • If the buildup is minimal and the passages are generally in good condition, cleaning may be sufficient.

2. Severity of Carbon Buildup:

   • If the carbon buildup is severe and difficult to remove, replacement may be necessary.

3. Condition of the Passages:

   • If the passages are damaged, corroded, or cracked, replacement is the best option.

4. Ease of Access:

   • Consider the ease of access to the air injection passages. If they are difficult to reach, cleaning may be more challenging and time-consuming.

5. Cost Comparison:

   • Compare the cost of cleaning versus replacement. In some cases, replacement may be more cost-effective in the long run.

Consulting with a qualified technician can also help you make the right decision based on your vehicle’s specific needs.

27. Troubleshooting Steps if the OBD2 Code 0491 Returns After Repair

If the OBD2 code 0491 returns after you’ve performed repairs, it indicates that there’s still an underlying issue that needs to be addressed. Here are some troubleshooting steps to follow:

1. Verify the Initial Repair:

   • Double-check that the initial repair was performed correctly and that all components were properly installed.

2. Check for Additional Issues:

   • Inspect the secondary air injection system for any additional issues that may have been overlooked during the initial diagnosis.

3. Re-Evaluate Oxygen Sensor Readings:

   • Use an OBD2 scanner to re-evaluate the oxygen sensor readings and ensure they are within the normal range.

4. Perform a Smoke Test:

   • Conduct a smoke test to check for any vacuum leaks that may have developed since the initial repair.

5. Check the ECU Software:

   • Ensure that the ECU software is up to date and that there are no known issues that could be causing the code to return.

6. Consult a Professional:

   • If you’re unable to resolve the issue on your own, consult a qualified technician for further assistance.

28. How to Use a Multimeter to Diagnose Electrical Issues in the Secondary Air Injection System

A multimeter is an essential tool for diagnosing electrical issues in the secondary air injection system. Here’s how to use a multimeter effectively:

1. Gather Your Supplies:

   • Multimeter
   • Wiring diagram for your E39 model
   • Safety glasses
   • Gloves

2. Set Up the Multimeter:

   • Set the multimeter to the appropriate setting for the test you’re performing (e.g., voltage, continuity, resistance).

3. Voltage Test:

   • Use the multimeter to check for voltage at various points in the system, such as the air pump connector and the vacuum switch.
   • Consult your vehicle’s wiring diagram for the correct voltage readings.

4. Continuity Test:

   • Use the multimeter to check for continuity in the wiring.
   • Disconnect the battery before performing this test.
   • Check for continuity between the various components of the secondary air injection system.

5. Resistance Test:

   • Use the multimeter to measure the resistance of various components, such as the oxygen sensors.
   • Consult your vehicle’s repair manual for the correct resistance values.

By following these steps, you can effectively use a multimeter to diagnose electrical issues in the secondary air injection system and identify the root cause of the OBD2 code 0491.

29. Understanding the Relationship Between the Secondary Air Injection System and Catalytic Converters

The secondary air injection system and catalytic converters work together to reduce harmful emissions. The secondary air injection system pumps air into the exhaust stream during cold starts to help burn off excess hydrocarbons. This process helps the catalytic converters reach their operating temperature more quickly, allowing them to more effectively convert pollutants into less harmful substances.

• Reducing Hydrocarbons: The secondary air injection system helps reduce hydrocarbon emissions during cold starts.