P1408 – EGR Flow Out of Self-Test Range

Urgency and Safety

• It is generally safe to drive a short distance with a P1408 code to get the vehicle diagnosed and repaired. However, driving for extended periods is not recommended as it can lead to reduced fuel economy, increased emissions, and potential engine damage.
• The issue should be addressed as soon as possible to prevent further damage and restore proper engine performance. While it may not require immediate service, it should not be ignored for long.
• If the vehicle experiences significant power loss, rough running, or stalling, it should not be driven until the problem is resolved.

Code Basics

• The P1408 code indicates that the Exhaust Gas Recirculation (EGR) system flow is out of the expected range during the EGR system self-test.
• The general definition of P1408 is consistent across most makes and models. However, the specific EGR system configuration and components may vary.
• The main components involved when the P1408 code is triggered are the EGR valve, EGR vacuum regulator solenoid, Differential Pressure Feedback EGR (DPFE) sensor, and the associated vacuum lines and electrical circuits.

Parts and Operation

• The EGR system redirects a portion of the exhaust gases back into the intake manifold to reduce combustion temperatures and NOx emissions.
• The EGR valve controls the flow of exhaust gases into the intake. It is typically operated by engine vacuum and controlled by the PCM.
• The DPFE sensor measures the pressure differential across a metering orifice to provide feedback on EGR flow to the PCM.
• Vacuum lines carry the vacuum signal to the EGR valve and EGR vacuum regulator solenoid. Electrical connections provide power and signal paths between components and the PCM.
• During operation, the PCM commands the EGR vacuum regulator solenoid to apply vacuum to the EGR valve, opening it and allowing exhaust flow. The DPFE sensor signal is used to monitor and adjust the EGR flow for optimum performance.

Common Causes

• Vacuum leaks in the EGR system hoses and connections are a common cause of P1408.
• A stuck open or stuck closed EGR valve can lead to incorrect EGR flow.
• Restrictions in the EGR passages or a clogged EGR valve can limit flow and trigger the code.
• Electrical faults in the DPFE sensor circuit, EGR solenoid circuit, or damaged wiring can result in incorrect EGR system operation.
• In some Ford vehicles, a leaking EGR valve gasket is a common issue that allows the EGR valve to draw in air and trigger a P1408.

Diagnosis and Troubleshooting

1. Visually inspect the EGR system, checking for loose or damaged vacuum lines, electrical connections, and obvious damage.
2. Connect a scan tool and check for additional trouble codes that may help pinpoint the problem. Clear the codes and test drive to see if P1408 returns.
3. Perform a visual and physical inspection of the EGR valve, looking for signs of sticking or deposits.
4. Test the DPFE sensor by monitoring the voltage signal with the EGR disconnected (should be around 0.75V) and then applying vacuum (should be over 3V).
5. Check the vacuum supply to the EGR valve and the EGR vacuum regulator solenoid using a vacuum gauge.
6. Inspect the EGR passages for blockage and clean if necessary.
7. Test the resistance of the EGR solenoid coil (should be 20-30 ohms) and check the connector for power and ground.
8. A digital multimeter, vacuum gauge, and scan tool are essential for proper diagnosis.
9. Common mistakes include not thoroughly checking for vacuum leaks and not verifying the DPFE sensor signal before replacing parts.

Repair Solutions

• If vacuum leaks are found, replace the damaged lines or hoses and secure all connections.
• For a stuck EGR valve, remove the valve and clean the pintle and passages. If badly stuck or damaged, replacement may be necessary.
• Blockages in the EGR passages should be carefully cleaned and the EGR valve gasket replaced if leaking.
• Faulty DPFE sensors, EGR vacuum solenoids, and damaged wiring should be replaced as needed.
• When replacing the EGR valve, use a new gasket and tighten the mounting bolts to the manufacturer's specified torque (typically 7-10 lb-ft or 10-14 N·m).

Repair Costs

• The average cost to diagnose and repair a P1408 code ranges from $75 to $150 in parts and $100 to $200 in labor.
• The EGR valve is usually the most expensive part, ranging from $50 to over $200 for some vehicles. The DPFE sensor typically costs between $30 and $100.
• In most cases, total repair costs fall between $175 and $350 (€150 to €300). However, luxury and performance vehicles may have significantly higher parts costs.

Prevention and Maintenance

• Regular maintenance, including oil changes and air filter replacements, can help reduce carbon buildup in the EGR system.
• Periodic inspection of vacuum lines and electrical connections can catch problems before they trigger a code.
• If the EGR valve is sticking or the engine is idling roughly, cleaning the EGR passages and valve can often restore proper operation.

Related Issues

• Other codes that may appear with P1408 include P0401 (insufficient EGR flow), P0402 (excessive EGR flow), and P1409 (EGR vacuum regulator solenoid circuit malfunction).
• Symptoms related to EGR system faults include rough idling, hesitation on acceleration, increased fuel consumption, and a failed emissions test.
• EGR issues can lead to increased combustion temperatures, which may cause knock sensor codes or even engine damage if left unresolved.

By following this diagnostic and repair guide, engineers and mechanics should be able to efficiently troubleshoot and resolve vehicles displaying a P1408 trouble code. Proper diagnosis and repair will restore engine performance, reduce emissions, and help prevent further damage to the EGR system and related components.

Frequently Asked Questions About P1408

What does the P1408 code mean?

The P1408 code indicates that the Exhaust Gas Recirculation (EGR) system flow is out of the expected range during the EGR system self-test.

Is it safe to drive with a P1408 code?

It is generally safe to drive a short distance with a P1408 code to get the vehicle diagnosed and repaired. However, driving for extended periods is not recommended as it can lead to reduced fuel economy, increased emissions, and potential engine damage.

What are the common symptoms of a P1408 code?

Common symptoms include rough idling, hesitation on acceleration, increased fuel consumption, and a failed emissions test.

What are the main components involved with the P1408 code?

The main components involved are the EGR valve, EGR vacuum regulator solenoid, Differential Pressure Feedback EGR (DPFE) sensor, and the associated vacuum lines and electrical circuits.

How does the EGR system work?

The EGR system redirects a portion of the exhaust gases back into the intake manifold to reduce combustion temperatures and NOx emissions. The EGR valve controls the flow, operated by engine vacuum and controlled by the PCM.

What are common causes of a P1408 code?

Common causes include vacuum leaks in the EGR system hoses, a stuck open or closed EGR valve, restrictions in the EGR passages, electrical faults in the DPFE sensor or EGR solenoid circuits, and damaged wiring.

How is a P1408 code diagnosed?

Diagnosis involves visually inspecting the EGR system components, checking for additional codes, testing the DPFE sensor signal and EGR valve operation, and verifying vacuum supply and electrical connections.

What tools are needed to diagnose a P1408 code?

A digital multimeter, vacuum gauge, and scan tool are essential for proper diagnosis of P1408.

What are the common mistakes when diagnosing P1408?

Common mistakes include not thoroughly checking for vacuum leaks and not verifying the DPFE sensor signal before replacing parts.

How is a P1408 code repaired?

Repairs involve replacing damaged vacuum lines, cleaning or replacing the EGR valve and passages as needed, and addressing any electrical faults found in the DPFE sensor or EGR solenoid circuits.

What is the average cost to fix a P1408 code?

The average cost to diagnose and repair a P1408 code ranges from $75 to $150 in parts and $100 to $200 in labor. The EGR valve is usually the most expensive part.

Can regular maintenance help prevent EGR system issues?

Yes, regular maintenance like oil changes and air filter replacements can help reduce carbon buildup in the EGR system. Periodic inspection of vacuum lines and electrical connections can catch problems early.

Are there any TSBs or recalls related to P1408?

There are no known TSBs or recalls that specifically address the P1408 code. However, some vehicle-specific TSBs for EGR system issues may be applicable.

Can a P1408 code cause other issues if left unrepaired?

Yes, EGR issues can lead to increased combustion temperatures, which may cause knock sensor codes or even engine damage if left unresolved.

Is the definition of P1408 the same across all makes and models?

The general definition of P1408 is consistent across most vehicles, indicating an EGR flow malfunction. However, the specific components and configuration of the EGR system can vary between makes and models.

Can a P1408 code be caused by issues other than the EGR system?

While less common, a P1408 code can potentially be triggered by faults in other systems that affect EGR operation, such as the Powertrain Control Module (PCM) or engine vacuum supply.

How do I clear a P1408 code?

A P1408 code can be cleared using a scan tool or disconnecting the battery. However, if the underlying issue is not repaired, the code will likely reappear.

What other codes may appear along with P1408?

Related codes that may appear alongside P1408 include P0401 (insufficient EGR flow), P0402 (excessive EGR flow), and P1409 (EGR vacuum regulator solenoid circuit malfunction).

Can a P1408 code affect vehicle performance?

Yes, a malfunctioning EGR system can cause reduced engine performance, rough running, and increased emissions.

Is it possible for a P1408 code to be intermittent?

Yes, depending on the root cause, a P1408 code may be intermittent and only occur under certain driving conditions or after a specific amount of drive time.

By understanding the causes, symptoms, diagnosis, and repair of the P1408 code, vehicle owners and technicians can more effectively address EGR system malfunctions and restore proper engine performance.