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P1408

EGR Flow Out Of Self Test Range.

  • Other
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
4
AreaAuxiliary emission controls
08
FaultThe specific fault in that area

What it means

P1408 is a manufacturer-specific code, and this guide covers the 'EGR Flow Out Of Self Test Range' meaning used by Ford and Mazda-type systems. The same code means something different on other makes, such as an intake manifold pressure sensor circuit fault or an EGR temperature sensor fault, so confirm the definition for your vehicle. Here the control unit ran its EGR self-test and measured exhaust gas flow outside the expected range, either too low or too high, for the commanded valve position.

Symptoms

  • Engine warning light on
  • Rough or unstable idle
  • Hesitation or surging at light throttle
  • Pinking or knocking under load if EGR flow is too low
  • Stalling or poor running at idle if the valve is stuck open
  • Failed emissions test

Possible causes

  • Carbon blocked EGR passages or pipe, restricting flowlikely
  • EGR valve sticking or not seating or opening fullylikely
  • Faulty EGR flow or pressure feedback sensor, or its hoses blocked, split or disconnectedlikely
  • Vacuum leak, split hose or faulty vacuum solenoid or regulator feeding the EGR valve (where fitted)possible
  • Wiring or connector fault on the EGR valve, solenoid or sensor circuitspossible
  • Exhaust restriction or leak upstream of the EGR take-off affecting the flow readingrare
  • Intake manifold pressure sensor fault giving a false reading during the testrare

How to diagnose

  1. Confirm the code definition for this make and model, then read freeze frame data and any other stored codes, dealing with related codes first.
  2. Visually inspect EGR hoses, vacuum lines, pipes, wiring and connectors for splits, disconnection, heat damage, corrosion or exhaust leaks.
  3. With a scan tool, view the EGR feedback sensor reading with the engine off and compare it with the specification for the model.
  4. Command the EGR valve open and closed with the scan tool and watch for a change in idle quality and sensor readings.
  5. Check vacuum supply to the valve and the solenoid operation, where the system is vacuum operated, and check for leaks.
  6. Remove the EGR valve and inspect it and the passages for carbon build-up and a valve that is stuck or not seating.
  7. Check the sensor and valve wiring for continuity, shorts and supply and reference voltages against the wiring diagram.
  8. Check for an exhaust restriction and verify the intake manifold pressure reading is plausible.

How to fix

  • Clean carbon from the EGR passages, pipe and valve seat, or replace parts that cannot be cleaned.
  • Replace the EGR valve if it sticks, leaks or fails to move correctly.
  • Replace the faulty EGR feedback sensor and renew any blocked or perished sensor hoses.
  • Repair vacuum leaks and replace the faulty vacuum hose, solenoid or regulator.
  • Repair damaged wiring or connectors, then clear the code and retest the system.
  • Rectify any exhaust restriction or leak found, as the model requires.

Can I keep driving?

Medium severity

The car can usually be driven short-term, but fix it soon, as poor running, pinking under load or a failed emissions test can follow. If it runs very roughly, stalls or pinks heavily, limit driving until it is repaired.

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

This code for other makes

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