Technical Definition:

Exhaust Gas Recirculation (EGR) Flow Insufficient Detected

Trouble Code: P0401
Address: 0x0401
System: Powertrain
Subsystem: Auxiliary Emission Controls
Technical Description:

EGR stands for Exhaust Gas Recirculation. It is part of the vehicle emmissions system, and is used to reduce combustion temperature and pressure to control Oxides of Nitrogen. There are generally three parts to the EGR system: the EGR valve, an actuator solenoid, and a differential pressure sensor EGR (DPFE). These things work together to deliver the correct amount of recirculation based on engine temperature, load, etc. The P0401 code means that OBD detected an insufficient amount of EGR.

Possible Causes:
  • The DPFE (differential pressure feedback EGR) sensor is faulty and needs to be replaced
  • There is a blockage in the EGR (tube), most likely carbon buildup
  • The EGR valve is faulty
  • The EGR valve may not be opening due to a lack of vaccuum

Possible Symptoms:

Exhaust Gas Recirculation Flow Insufficient Detected

Possible Solutions:
  • Use a vacuum pump and pull the EGR valve open while monitoring engine RPM’s & DPFE voltage. There should be a noticable difference in RPM’s with the EGR open
  • Clean out the EGR valve and/or tubing to remove deposits
  • Check the voltage at the DPFE, compare to specified values (refer to a repair manual for your specific model)
  • Replace the DPFE sensor (with a good quality / OEM one)
  • Replace the EGR valve

OBD-II Trouble Code Type:

Diagnostic Step:

Tech Notes:

– EGR passage clogged
– Faulty EGR Vacuum Modulator Valve
– Faulty EGR Valve
– Faulty EGR solenoid valve
– EGR solenoid valve harness is open or shorted
– EGR solenoid valve circuit poor electrical connection
– Dead (Weak) battery
– Faulty EGR temperature sensor and circuit
– Exhaust gas leaks

Specific Makes:

– Possible engine hesitation

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