DTC P0401: Exhaust Gas Recirculation Flow Insufficient Detected

TECHNICAL DESCRIPTION

• When the EGR valve (stepper motor) is actuated from the fully closed position toward the open position while the engine is running, EGR gas flows.
  
• The ECM checks how the EGR gas flow signal changes.
  

DESCRIPTIONS OF MONITOR METHODS

Small manifold pressure change during exhaust gas recirculation (EGR) operation from closed to open.

MONITOR EXECUTION

Continuous

MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)

• EGR stepper motor monitor
  

• Mass airflow sensor
  
• Engine coolant temperature sensor
  
• Intake air temperature sensor
  
• Barometric pressure sensor
  
• Accelerator pedal position sensor
  
• Manifold absolute pressure sensor
  

DTC SET CONDITIONS

• At least 20 seconds have passed since the last monitor was complete.
  
• Engine coolant temperature is higher than 76°C (169°F).
  
• Engine speed is between 1,188 and 2,500 r/min <M/T> or 1,125 and 2,500 r/min <CVT>.
  
• Intake air temperature is higher than -10°C (14°F).
  
• Barometric pressure is higher than 76 kPa (22.4 in.Hg).
  
• Fuel is being shut off.
  
• Vehicle speed is 30 km/h (19 mph) or more.
  
• At least 90 seconds have passed since manifold absolute pressure sensor output voltage fluctuated 1.5 volts or more.
  
• Battery positive voltage is higher than 10.3 volts.
  
• Accelerator pedal is closed.
  
• Volumetric efficiency is lower than 24 percent.
  
• The ECM monitors for this condition for 3 cycles of 1.8 seconds each during the drive cycle.
  

• When the EGR valve opens to the prescribed opening, when intake manifold pressure fluctuation width is lower than 2.5 kPa (0.74 in.Hg).
  

OBD-II DRIVE CYCLE PATTERN

Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 3 .

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are: )

• Contaminated EGR valve and EGR passage.
  
• ECM failed.
  

Refer to GROUP 17, Emission Control System - Exhaust Gas Recirculation (EGR) System - General Information .

	Repair it. Then go to Step 3.

	Go to Step 2.

	Repair the EGR valve and the EGR passage contamination.

	Go to Step 3.

(1)Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 3 .

	Retry the troubleshooting.

	The inspection is complete.