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P1406

DPFE Sensor Downstream Hose Off Or Plugged.

  • Mazda
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
4
AreaAuxiliary emission controls
06
FaultThe specific fault in that area

What it means

On Mazda, P1406 means the control unit has detected a fault with the downstream (low pressure) hose of the differential pressure feedback EGR (DPFE) sensor, which is either off or blocked. The DPFE sensor measures the pressure drop across a restrictor in the EGR system to work out EGR flow. The ECU saw a pressure signal that did not match what it expected, pointing to a disconnected, split or blocked sensing hose or passage.

Symptoms

  • Engine warning light on
  • Rough or unstable idle
  • Hesitation or poor response under light load
  • Slight pinking or knocking under acceleration
  • Poor fuel economy
  • Failed emissions test

Possible causes

  • Downstream DPFE hose disconnected, split, perished or loose at the sensor or EGR pipelikely
  • Downstream hose or its metal pipe blocked with carbon or condensationlikely
  • Carbon blockage in the EGR orifice or restrictor tube fitting that feeds the hoselikely
  • Faulty DPFE sensor giving an incorrect signalpossible
  • Wiring or connector fault on the sensor reference, signal or earth circuitpossible
  • EGR valve stuck open or closed causing an unexpected pressure readingpossible
  • Fault within the engine control unitrare

How to diagnose

  1. Read all stored and pending codes and note the freeze frame data, then check for any other EGR or fuel trim codes.
  2. Visually inspect the DPFE sensor hoses, especially the downstream one, for being off, kinked, cracked, melted or loose at both ends.
  3. Check the sensor connector and wiring for damage, corrosion, water ingress or poor pin tension.
  4. Disconnect the hose and check that it and the metal pipe are clear by gently blowing through them, and look for carbon or moisture.
  5. Inspect the EGR orifice or restrictor fitting for carbon build-up. The layout varies by model and engine, so follow the manufacturer's procedure.
  6. With the engine off, check the sensor reference voltage, signal and earth with a multimeter against the specification.
  7. Using live data, compare the sensor reading at key-on and at idle, then watch it respond when the EGR valve is operated, if the system allows.
  8. Check that the EGR valve moves freely and seals properly, using the manufacturer's test procedure for the model.

How to fix

  • Refit, secure or replace any hose that is off, split or perished.
  • Clear blocked hoses and pipes, replacing any that cannot be cleaned fully.
  • Remove carbon from the EGR passages and restrictor as per the manufacturer's procedure, or replace the affected part.
  • Replace the DPFE sensor if its readings are out of specification with the hoses and wiring confirmed good.
  • Repair damaged wiring or connectors, then clear the code and road test to confirm it stays away.

Can I keep driving?

Medium severity

The car can usually be driven for a short time, but book it in soon. Faulty EGR control can cause poor running, higher emissions and increased engine pinking, and a blocked passage will tend to get worse.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.

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