P1406 – Exhaust Flap Position Sensor Circuit Low (some manufacturers)

What is the P1406 Code?

The P1406 code indicates an issue with the Exhaust Gas Recirculation (EGR) valve position sensor circuit. It is a manufacturer-specific code used by some makes like Ford, GM, and Isuzu.

Urgency and Severity

The urgency of addressing P1406 depends on the specific situation:

• In most cases, you can continue driving cautiously but should diagnose and repair the issue as soon as possible to prevent potential damage to the EGR system or catalytic converter.
• However, if the code is causing significant engine performance issues or the check engine light is flashing, you should stop driving and have the vehicle towed to a mechanic for diagnosis.

Systems and Parts Involved

The main components related to the P1406 code are:

• EGR Valve: Allows small amounts of exhaust gas to recirculate back into the engine to lower combustion temperatures and reduce NOx emissions.
• EGR Position Sensor: Monitors the actual position of the EGR valve pintle and sends a signal to the PCM.
• Wiring and Connectors: Carries the reference voltage, ground, and position signal between the sensor and PCM.

Common Causes

Some typical causes of the P1406 code include:

• Carbon buildup on the EGR valve preventing it from fully closing
• Faulty EGR valve position sensor providing an inaccurate signal
• Damaged or disconnected EGR position sensor wiring/connectors
• Blocked or restricted EGR passages or hoses
• In rare cases, a failed PCM

Diagnosis Steps

1. Scan for all codes and document freeze frame data.
2. Visually inspect the EGR valve, hoses, wiring and connectors for obvious faults.
3. Test the EGR valve for proper operation using a scan tool bidirectional controls.
4. Check the reference voltage, ground, and position signal at the EGR sensor connector.
5. If no wiring faults are found, replace the EGR position sensor.
6. If the code persists, perform a smoke test to check for EGR system leaks.
7. Clean or replace the EGR valve and passages as needed.

Repair Costs

The cost to diagnose and repair a P1406 code can vary depending on the root cause:

• Diagnosis and testing: $75-150 USD / €65-130 EUR
• EGR position sensor replacement: $125-350 USD / €110-300 EUR
• EGR valve replacement: $250-600 USD / €220-525 EUR
• Cleaning EGR system: $100-250 USD / €90-220 EUR

Prevention and Related Issues

To help prevent EGR system issues:

• Use high quality fuel and change the oil regularly
• Address any performance issues promptly
• Clear any EGR system codes properly after repairs

Other codes potentially related to P1406 include P0400 (EGR flow malfunction), P0401 (insufficient EGR flow), and P0402 (excessive EGR flow). The EGR system works closely with the fuel trim and emission controls.

Frequently Asked Questions About P1406 Code

What does the P1406 code mean?

The P1406 code indicates that the EGR valve position sensor signal is outside the normal range, either above the maximum limit or below the minimum threshold expected by the PCM. This suggests a problem with the EGR valve position sensor or circuit.

What are the common causes of the P1406 code?

Common causes of P1406 include:

• Faulty EGR valve position sensor
• Damaged or corroded EGR valve position sensor wiring or connectors
• Excessive carbon buildup on the EGR valve causing it to stick
• Malfunctioning EGR valve solenoid
• Vacuum leaks in the EGR system hoses
• In rare cases, a failed PCM

What are the symptoms of the P1406 code?

Symptoms you may notice with P1406 include:

• Check engine light illuminated
• Rough idle or stalling
• Increased fuel consumption
• Reduced engine power, especially at low RPM
• Vehicle may be hard to start
• Failed emissions test

Is it safe to drive with the P1406 code?

In most cases, you can continue driving cautiously with P1406 for a short period. However, you should diagnose and repair the issue as soon as possible to prevent potential catalytic converter or engine damage from improper EGR flow. If drivability issues are severe, have the vehicle towed to avoid unsafe driving conditions.

How do you diagnose the P1406 code?

To diagnose P1406, a technician will typically:

1. Scan for all codes and document freeze frame data.
2. Visually inspect the EGR valve, hoses, wiring and connectors.
3. Test the EGR valve for proper operation using a scan tool.
4. Check the reference voltage, ground, and position signal at the sensor.
5. Perform a smoke test to check for EGR system vacuum leaks.
6. Clean or replace the EGR valve and passages as needed.

Can I diagnose the P1406 code myself?

Diagnosing P1406 requires intermediate automotive knowledge and tools like an OBD-II scanner and digital multimeter. If you are comfortable testing electrical components and familiar with the EGR system, you can perform basic diagnostics. However, it's best to consult a professional if you are unsure how to proceed.

How much does it cost to repair the P1406 code?

The cost to repair P1406 ranges from $100-600 depending on the root cause:

• Diagnosis and testing: $75-150
• EGR position sensor replacement: $125-350
• EGR valve replacement: $250-600
• Cleaning EGR system: $100-250

Can a clogged EGR valve cause the P1406 code?

Yes, a clogged EGR valve is a common cause of P1406. Carbon deposits can build up on the EGR valve over time, causing it to stick open or closed. This results in the position sensor reading being out of range and setting the code.

Can a vacuum leak cause the P1406 code?

Yes, vacuum leaks are a possible cause of P1406, especially on older vehicles with vacuum-operated EGR valves. A leak in the EGR vacuum hoses or connections can cause incorrect EGR valve operation and position sensor readings.

Can a weak battery cause the P1406 code?

Not directly, as a weak battery itself doesn't impact EGR valve operation. However, low battery voltage can cause multiple random codes to be set, including P1406 in some cases. Always ensure the battery is fully charged and test the charging system if you suspect this issue.

How do I test an EGR valve position sensor?

To test an EGR valve position sensor:

1. Locate the EGR valve and position sensor, typically near the top of the engine.
2. Unplug the sensor electrical connector.
3. Set your multimeter to DC volts.
4. Connect the multimeter leads to the sensor signal wire and ground.
5. With the key on, engine off, you should see a steady reference voltage between 4.8-5.0 V.
6. Manually operate the EGR valve from closed to open. The voltage should smoothly increase or decrease.
7. If you see supply voltage with the sensor disconnected, the wiring may be shorted to power.
8. If you see 0 V, the sensor signal wire may be open or shorted to ground.

How do I clean an EGR valve?

To clean an EGR valve:

1. Disconnect the negative battery cable.
2. Remove the EGR valve from the engine, leaving the electrical connector and hoses attached if possible.
3. Spray the EGR valve and passages liberally with throttle body cleaner.
4. Allow the cleaner to soak for 10-15 minutes to dissolve carbon deposits.
5. Use a pipe cleaner or small brush to remove any remaining debris.
6. Reinstall the EGR valve using a new gasket.
7. Reconnect the battery and clear any codes.
8. Test drive the vehicle to verify proper operation.

How often should I replace my EGR valve?

There is no specific service interval for EGR valve replacement. Most EGR valves will last the lifetime of the vehicle with proper maintenance. However, if the valve becomes significantly clogged with carbon, sticks open or closed, or exhibits electrical issues, replacement may be necessary to restore proper operation.

Can I replace just the EGR valve position sensor?

In many cases, yes. The EGR position sensor is often a separate component from the EGR valve itself. If diagnostic tests determine the sensor is faulty but the valve is operating normally, you can replace only the sensor. However, on some vehicles the sensor is integrated into the EGR valve, requiring replacement of the entire assembly.

What happens if I unplug the EGR valve?

Unplugging the EGR valve electrically will cause the valve to remain closed, as it can no longer receive an open command from the PCM. This will likely set a check engine light and P1406 code. While plugging the EGR ports and disabling the system was a common emissions bypass on older vehicles, it can cause drivability issues and increased NOx emissions on modern engines.

Will disconnecting the battery clear the P1406 code?

Disconnecting the battery will clear the P1406 code and turn off the check engine light temporarily. However, if the underlying problem that caused the code is not repaired, the code will return after driving the vehicle for some time. Clearing codes without performing repairs is not an effective long-term solution.

What does an EGR valve position sensor do?

The EGR valve position sensor, also known as an EGR valve feedback sensor, monitors the actual position of the EGR valve pintle and sends a signal voltage to the PCM. This allows the PCM to determine if the commanded EGR valve position matches the actual position for precise control of EGR flow.

How do I test EGR valve operation?

To perform a basic test of EGR valve operation:

1. Start the engine and allow it to idle.
2. Unplug the vacuum hose from the EGR valve.
3. Manually apply vacuum to the EGR valve using

   a hand vacuum pump.

4. The engine should stumble or stall if the EGR valve is opening and allowing exhaust flow.
5. If there is no change in idle, the EGR valve may be stuck closed or the passages may be clogged.
6. Inspect the EGR valve pintle for free movement and clean or replace the valve as needed.

Note that this test does not apply to newer electronic EGR valves. For those, use a scan tool to command the EGR valve open and closed while monitoring the position sensor voltage.

What other codes may be related to P1406?

Other codes potentially related to P1406 include:

• P0400 – EGR flow malfunction
• P0401 – Insufficient EGR flow
• P0402 – Excessive EGR flow
• P0403 – EGR circuit malfunction
• P0404 – EGR valve position sensor circuit intermittent
• P0405 – EGR valve position sensor circuit low
• P0406 – EGR valve position sensor circuit high
• P1400 – EGR valve stuck open
• P1401 – EGR valve stuck closed

Can the P1406 code cause damage to my engine?

Indirectly, yes. While the P1406 code itself does not cause engine damage, it indicates an issue with the EGR system that can have negative effects if left unrepaired. A stuck open EGR valve can lead to rough running, misfires, and increased temperatures that can damage the catalytic converter over time. A stuck closed EGR valve may cause combustion temperatures to rise, increasing the risk of pre-ignition or detonation under heavy load.