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 or the PCM 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
- Throttle position sensor
- Accelerator pedal position sensor
- Manifold absolute pressure sensor

DTC SET CONDITIONS

Logic Flow Chart:

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 1,100 and 1,750 r/min.
- Intake air temperature is higher than -10 °C (14 °F).
- Barometric pressure is higher than 76 kPa (22.4 in.Hg).
- Vehicle speed is 20 km/h (32 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 23.8 percent.
- The ECM or the PCM monitors for this condition for 3 cycles of 2.0 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 2.0 kPa (0.59 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.
- EGR valve (stopper motor) failed.
- Open or shorted EGR valve (stopper motor) circuit, or connector damage.
- Manifold absolute pressure sensor failed.
- ECM failed.
- PCM 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 Emission Control System - Exhaust Gas Recirculation (EGR) System - General Information.

Q: Are there any abnormalities?

YES: Repair it. Then go to Step 3.

NO: Go to Step 2.

STEP 2. Using scan tool MB991958, check data list item 8: Manifold Absolute Pressure Sensor.

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.

1. Connect scan tool MB991958 to the data link connector.
2. Start the engine and run at idle.
3. Set scan tool MB991958 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.

Q: Is the sensor operating properly?

YES: Clean the EGR valve and EGR passage. Then go to Step 3.

NO: 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 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.