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Exhaust gas recirculation (EGR)

P0400 Exhaust Gas Recirculation (EGR) Flow Malfunction

The ECU monitors EGR flow by comparing the expected effect of opening the EGR valve with feedback from sensors such as the MAF, intake manifold pressure or EGR position sensor. P0400 is set when the measured EGR flow does not match the commanded value under the test conditions.

Common causes

  • Carbon build-up in the EGR valve or passages
  • Sticking or failed EGR valve
  • Faulty EGR position, MAF or MAP sensor
  • Wiring or connector faults in the EGR circuit
  • Vacuum leaks or a faulty EGR control solenoid on vacuum-operated systems

Typical symptoms

  • Check engine light (MIL) on
  • Rough idle or hesitation
  • Reduced power or limp mode on some vehicles
  • Increased smoke or emissions

P0400 and NuoVolta

If the EGR system has been removed or blanked for off-road or motorsport use, where permitted by law, the NuoVolta EGR Removal solution adjusts the ECU calibration and the DTC removal feature can disable this code. On a vehicle with an intact EGR system, diagnose and repair the fault first.

EGR Removal Available for 256 ECUs

Related codes

P0401Exhaust Gas Recirculation (EGR) Flow Insufficient Detected P0402Exhaust Gas Recirculation (EGR) Flow Excessive Detected P0403Exhaust Gas Recirculation (EGR) Control Circuit Malfunction P0404Exhaust Gas Recirculation (EGR) Circuit Range/Performance P0405Exhaust Gas Recirculation (EGR) Sensor A Circuit Low P0406Exhaust Gas Recirculation (EGR) Sensor A Circuit High

Diagnose and repair real faults first. Removing or disabling emission systems is only permitted where allowed by law, for example for off-road or motorsport use.