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P1400

Differential Pressure Feedback Electronic Sensor Circuit Low Voltage.

  • Mercury
  • Powertrain
  • Manufacturer code
  • Low severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
4
AreaAuxiliary emission controls
00
FaultThe specific fault in that area

What it means

P1400 on a Mercury (Ford-family) vehicle means the Differential Pressure Feedback EGR (DPFE) sensor circuit is reading low voltage. The engine control unit monitors the DPFE sensor signal, which reports the pressure drop across a metering orifice in the exhaust gas recirculation (EGR) system. The code sets when the signal voltage stays below the expected range, pointing to an electrical fault or a sensor or hose problem.

Symptoms

  • Check engine light on
  • Rough idle or occasional stalling
  • Hesitation or poor driveability under light load
  • Pinging or detonation on acceleration
  • Poor fuel economy
  • Failed emissions test

Possible causes

  • Faulty DPFE sensor reading low or stuck at low voltagelikely
  • Disconnected, split, cracked or loose vacuum/pressure hoses to the DPFE sensorlikely
  • Damaged wiring, poor connector contact or corrosion in the DPFE signal, reference or ground circuitlikely
  • Signal circuit shorted to ground or open circuitpossible
  • Blocked or sooted EGR metering orifice or pressure tubes giving an abnormal readingpossible
  • Fault with the 5 volt reference supply or sensor ground at the control unitrare
  • Faulty engine control unitrare

How to diagnose

  1. Read all stored codes and freeze frame data, noting engine load, speed and temperature when the code set, then check for any related EGR codes
  2. Visually inspect the DPFE sensor, its connector and the wiring for chafing, heat damage, corrosion or bent pins
  3. Inspect the hoses between the sensor and the EGR tube for splits, kinks, loose fittings or blockage, and check the tube itself for cracks or leaks
  4. With the ignition on and engine off, view the DPFE sensor live data and compare it with the specification for your model and engine
  5. Check the 5 volt reference, signal and ground at the sensor connector with a multimeter against the wiring diagram
  6. Check the signal circuit for short to ground or open circuit with the control unit and sensor disconnected
  7. Check the EGR valve operation and look for blocked passages or a clogged orifice tube, following the procedure for your engine
  8. Compare sensor response when the EGR valve is commanded open, as the expected reading varies by model and engine

How to fix

  • Replace the DPFE sensor if its output is out of specification or does not respond
  • Replace or reconnect damaged hoses and fix any leaking or blocked pressure tubes
  • Repair wiring faults, and clean or replace corroded or damaged connector terminals
  • Clean or replace a blocked EGR orifice tube or related passages as the manufacturer's procedure allows
  • Repair the reference or ground supply fault, and only if all else is proven sound, diagnose and replace the control unit

Can I keep driving?

Low severity

The car can usually be driven short-term, but book it in soon as driveability, fuel economy and emissions may suffer. If it runs very roughly, stalls or pings heavily, limit driving until it is checked.

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

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