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P1406 – What Does It Mean and How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.

Definition

P1406 is an OBD-II Code that refers to DPFE Sensor Circuit Downstream Hose (Ford, Lincoln, Mercury)

Meaning

A P1406 code is a manufacturer specific diagnostic trouble code that occurs when the PCM/ECM detects an issue with the EGR (Exhaust Gas Recirculation) valve which has a sensor that detects the position of the EGR valve shaft. The EGR valve opens and closes with signal voltages ranging from 0.1 to 0.3 V which is stored in the memory when the valve is closed after a vehicle activation. During each ignition activation, the PCM compares this value to subsequent values of the closed position in order to maintain a consistent reading.

If the EGR shaft is 10 percent further forward than expected, the P1406 OBD2 diagnostic code will be set.

Causes

Common causes for this code include:

  • Downstream hose is plugged (ice)
  • Tubes are clogged or broken. Exhaust Gas Recirculation (EGR) tubes become blocked over time, typically from carbon buildup
  • The electrical connection between the Differential Pressure Feedback Electronic (DPFE) sensor and the control module is incorrect due to faulty wiring
  • Downstream hose is disconnected
  • The Electronic Differential Pressure Feedback (DPFE) sensor is faulty
  • The Differential Pressure Feedback Electronic (DPFE) sensor harness is open or shorted.

Symptoms

The symptoms of a P1406 code are:

  • The Check Engine Light will come on
  • It’s difficult to start the engine
  • The engine’s power is reduced
  • Idling irregularities
  • Engine stalling for no apparent reason
  • Engine knocking becomes more frequent as engine load is increased

Diagnosis

To diagnose a P1406 DTC code, a technician would:

  1. Scan for codes in the ECM and look at the freeze frame data for failure.
  2. Start by checking the condition of the downstream hose and tubes.
  3. Check the electrical connection between the DPFE sensor and the control module.
  4. Check for a broken or clogged exhaust tube.
  5. Inspect the DPFE sensor for damage.
  6. Check the wiring harness for an open or shorted circuit.
  7. If all of these tests come back normal, then it is likely that the EGR valve is stuck open and will need to be replaced.

Common mistakes

The following are some of the most common mistakes that a technician may make when diagnosing a P1406 code:

  • Not thoroughly inspecting all of the possible causes for the code
  • Not properly checking the electrical connection between the DPFE sensor and control module
  • Not thoroughly inspecting the exhaust tubes for damage or blockage
  • Assuming that the EGR valve is bad without first properly testing it
  • Not properly cleaning the DPFE sensor before testing it

How serious is this?

A P1406 code is considered to be a medium to high risk code. When the code is set, it means that there is an issue with the EGR valve and its sensor. This can cause a variety of problems with the engine, including stalling, reduced power, and knocking. It’s important to have this code diagnosed and repaired as soon as possible.

What repairs can fix the code?

The following are solutions that may fix this problem:

  • Check the condition of the downstream hose and tubes
  • Clean the DPFE sensor
  • Inspect the exhaust tubes for damage or blockage
  • Replace the EGR valve
  • Repair any faulty wiring

Related codes

A P1406 is related to and may be accompanied by the following codes:

P0401: EGR Flow Insufficient

P0505: Idle Speed Control System Malfunction

P0455: Evaporative Emission Control System Leak Detected (Large Leak)

P1400: Exhaust Gas Recirculation Valve Position Sensor Circuit Malfunction

Conclusion

In conclusion, the P1406 code is a manufacturer specific diagnostic trouble code that refers to a problem with the exhaust gas recirculation valve or its sensor. The code is set when the PCM detects a difference of 10 percent or more between the current and expected position of the EGR valve shaft. There are a number of possible causes for this code, including a clogged or broken exhaust tube, a faulty DPFE sensor, and incorrect wiring. The code is considered to be a medium to high risk code and should be repaired as soon as possible. Possible solutions include cleaning the DPFE sensor, inspecting the exhaust tubes for damage or blockage, and replacing the EGR valve.