P0401

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 stored in memory for the item monitored below)

- Exhaust gas recirculation (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
- Accelerator pedal position sensor
- Manifold absolute pressure 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 more than 76°C (169°F).
- Engine speed is between 1,250 and 2,500 r/min[M/T] or 1,188 and 2,500 r/min[CVT].
- Intake air temperature is more than -10°C (14°F).
- Barometric pressure is more than 76 kPa (22.4 in.Hg).
- Fuel is being shut off.
- Vehicle speed is more than 30 km/h (19 mph).
- At least 90 seconds have passed since manifold absolute pressure sensor output voltage fluctuated more than 1.5 volts.
- Battery positive voltage is more than 10.3 volts.
- Accelerator pedal is not depressed.
- Volumetric efficiency is less than 20 percent[M/T] or 24 percent[CVT].
- The ECM monitors for this condition for 3 cycles of 1.8 seconds each during the drive cycle.
Judgement Criterion

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

FAIL-SAFE AND BACKUP FUNCTION

- None

OBD-II DRIVE CYCLE PATTERN

Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 3 Monitors, Trips, Drive Cycles and Readiness Codes .

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

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


DIAGNOSIS

Required Special Tool:

- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991910: Main Harness A

STEP 1. Check the EGR system

Description and Operation.

Q. Are there any abnormalities?

YES Repair it. Then go to Step 4.
NO Go to Step 2.
STEP 2. Check the EGR valve contamination and the EGR passage contamination.

Q. Are the EGR valve and the EGR passage clogged?

YES Repair the EGR valve and the EGR passage contamination. Then go to Step 4.
NO 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 Monitors, Trips, Drive Cycles and Readiness Codes.

(2)Check the diagnostic trouble code (DTC).

Q. Is DTC P0401 set?

YES Replace the ECM (Refer to, Removal and Installation Removal and Replacement).
Then go to Step 4.
NO It can be assumed that this malfunction is intermittent. 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 Monitors, Trips, Drive Cycles and Readiness Codes.

(2)Check the diagnostic trouble code (DTC).

Q. Is DTC P0401 set?

YES Retry the troubleshooting.
NO The inspection is complete.