P0401

DTC P0401: Exhaust Gas Recirculation Flow Insufficient Detected [California]

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)
- 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 higher than 76 °C (169 °F).
- Engine speed is at between 1,250 and 2,500 r/min [M/T] or 1,188 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 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, 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. OBD-II Drive Cycle

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Contaminated EGR valve and EGR passage.
- ECM failed.

DIAGNOSIS

Required Special Tools:
- 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

Refer to Exhaust Gas Recirculation (EGR) System.

Q: Are there any abnormalities?

YES : Repair it. Then go to Step 3.

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.

NO : Go to Step 3.

STEP 3. 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. OBD-II Drive Cycle
2. Check the diagnostic trouble code (DTC).

Q: Is DTC P0401 set?

YES : Retry the troubleshooting.

NO : The inspection is complete.