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DTC codes / Ford codes / P1406

P1406 · FordDifferential Pressure Feedback Electronic Sensor Circuit Downstream Hose

P1406 on Ford vehicles indicates that the powertrain control module (PCM) has detected an electrical fault in the downstream hose circuit of the differential pressure feedback electronic (DPFE) sensor, which monitors exhaust pressure across the EGR system. The PCM compares the sensor's signal voltage on the downstream hose to expected values and sets this code when the circuit is open, shorted, or out of range.

SystemPowertrain
Code typeFord specific
SeverityMedium
Fix difficultyIntermediate
AreaAuxiliary emission controls

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms.
  • Slight hesitation or stumble during light acceleration due to incorrect EGR flow.
  • Reduced fuel economy as the PCM may default to a less efficient calibration.
  • Intermittent rough idle or surging if the faulty hose causes erratic pressure readings.
  • Failed emissions test because the EGR monitor will not complete.

Common causes, most likely first

  1. Cracked, disconnected, or melted downstream hose between the DPFE sensor and the EGR tube.
  2. Internal failure of the DPFE sensor causing an out-of-range signal on the downstream circuit.
  3. Corroded or damaged electrical connector at the DPFE sensor.
  4. Open or shorted wire in the downstream hose signal circuit between the sensor and PCM.
  5. Exhaust blockage or excessive backpressure from a restricted catalytic converter or muffler.
  6. Carbon buildup in the EGR passages altering pressure differentials and confusing the sensor.

How to diagnose and fix it

  1. Inspect the downstream hose for cracks, soft spots, or disconnection and replace it if damaged.
  2. Check the electrical connector at the DPFE sensor for corrosion, tightness, and pin damage.
  3. Measure reference voltage and signal voltage at the sensor connector with a digital multimeter and compare to Ford specifications.
  4. Perform a continuity and short-to-ground test on the downstream hose signal wire between the sensor and PCM.
  5. Test the DPFE sensor with a vacuum pump and multimeter to verify it produces a linear voltage change.
  6. Check for exhaust backpressure using a pressure gauge at the upstream oxygen sensor port to rule out a restricted converter.
  7. Clear the code and run the EGR monitor to confirm the repair before returning the vehicle.

DPFE hose faults that mimic sensor failure

  • A loose or cracked downstream hose often sets P1406 without any driveability complaint, so many technicians replace the sensor unnecessarily when only the hose is at fault.
  • The DPFE sensor on Ford engines is heat-sensitive, and a sensor that tests fine cold can drop out when hot, so perform voltage tests both cold and after a road test.
  • Exhaust backpressure from a partially clogged catalytic converter can skew DPFE readings and set this code even when the hose and sensor are electrically perfect.
  • After replacing the DPFE sensor or hose, the PCM may need to relearn the EGR position, so clearing the code and completing a drive cycle is essential to avoid a false return.
  • Corrosion inside the sensor connector pins is a common hidden cause on older Ford trucks, and a visual check alone may miss it without a pin drag test.

Can I keep driving with P1406?

You can usually continue driving with P1406 because the PCM defaults to a safe EGR strategy, but avoid long trips or heavy towing until repaired. If you notice rough running or reduced power, have the vehicle checked promptly to prevent further emissions system damage.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for Ford vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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