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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)
Other Monitor (There is no temporary DTC set in memory for the item monitored below)
  • EGR stepper motor monitor
Sensor (The sensor below is determined to be normal)
  • Mass airflow sensor
  • Engine coolant temperature sensor
  • Intake air temperature sensor
  • Barometric pressure sensor
  • Manifold absolute pressure sensor
  • Accelerator pedal position sensor
 
 
DTC SET CONDITIONS
Logic Flow Chart
 
 
Check 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 at between 906 and 2,500 r/min.
  • 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.
  • The accelerator pedal is closed.
  • Volumetric efficiency is lower than 28 percent.
  • The ECM monitors for this condition for 3 cycles of 2.2 seconds each during the drive cycle.
Judgment Criterion
  • When the EGR valve opens to the prescribed opening, when intake manifold pressure fluctuation width is lower than 2.0 kPa (0.59 in.Hg).
 
 
FAIL-SAFE AND BACKUP FUNCTION
  • None
 
 
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:)
  • EGR valve (stepper motor) failed.
  • Open or shorted EGR valve (stepper motor) circuit, or connector damage.
  • Manifold absolute pressure sensor failed.
  • ECM failed.

 
 
DIAGNOSIS
Required Special Tools:
  • MB992744: Vehicle Communication Interface-Lite (V.C.I.-Lite)
  • MB992745: V.C.I.-Lite Main Harness A
  • MB992747: V.C.I.-Lite USB Cable Short
  • MB992748: V.C.I.-Lite USB Cable Long
  • MB991958: Scan Tool (M.U.T.-III Sub Assembly)
    • MB991824: Vehicles Communication Interface (V.C.I.)
    • MB991827: M.U.T.-III USB Cable
    • MB991910: M.U.T.-III Main Harness A (Vehicles with CAN communication system)
STEP 1. Using scan tool (M.U.T.-III), check data list item 8: Manifold Absolute Pressure Sensor.
cautionTo prevent damage to scan tool (M.U.T.-III), always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool (M.U.T.-III).
(1) Connect scan tool (M.U.T.-III). Refer to HOW TO CONNECT THE SCAN TOOL (M.U.T.-III) .
(2) Start the engine and run at idle.
(3) Set scan tool (M.U.T.-III) to the data reading mode for item 8, Manifold Absolute Pressure Sensor.
(4) Warm up the engine to normal operating temperature: 80°C to 95°C (176°F to 203°F).
  • Should be between 16 - 36 kPa (4.7 - 10.6 in.Hg) at engine idling.
(5) Turn the ignition switch to the "LOCK" (OFF) position.
Is the sensor operating properly?
Clean the EGR valve and EGR passage. Then go to Step 2.
Refer to DTC P0106 - Manifold Absolute Pressure Sensor Circuit Range/Performance Problem , DTC P0107 - Manifold Absolute Pressure Sensor Circuit Low Input , DTC P0108 - Manifold Absolute Pressure Sensor Circuit High Input .
 
STEP 2. Check the EGR system
Refer to GROUP 17, Emission Control - Exhaust Gas Recirculation (EGR) System - General Information (Exhaust Gas Recirculation) .
Are there any abnormalities?
Repair it. Then go to Step 4.
Go to Step 3.
 
STEP 3. Check the trouble symptoms.
(1) Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 3 .
(2) Check the diagnostic trouble code (DTC).
Is DTC P0401 set?
Replace the ECM (Refer to Removal and Installation ). Then go to Step 4.
It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions .
 
STEP 4. Test the OBD-II drive cycle.
(1) Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 3 .
(2) Check the diagnostic trouble code (DTC).
Is DTC P0401 set?
Retry the troubleshooting.
The inspection is complete.