P0401

DTC P0401: Exhaust Gas Recirculation Flow Insufficient Detected

TECHNICAL DESCRIPTION
- When the EGR vacuum regulator solenoid valve switches from "OFF" to "ON" while the engine is running, EGR gas flows.
- The ECM or 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 vacuum regulator solenoid valve monitor
Sensor (The sensor below is determined to be normal)
- Volume airflow sensor
- Engine coolant temperature sensor
- Intake air temperature sensor
- Barometric pressure sensor
- Throttle 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 1,000 and 1,650 or 910 and 1,650 r/min.
- Intake air temperature is higher than 10° C (50° F).
- Barometric pressure is higher than 76 kPa (22.4 in.Hg).
- Vehicle speed is 1.5 km/h (1.0 mph) or 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.
- The throttle valve is closed.
- Volumetric efficiency is lower than 18 or 28 percent.
- While fuel is being shut off.
- 20 seconds have elapsed from the start of the previous monitoring.
- The ECM or PCM monitors for this condition for 3 cycles of 2 seconds each during the drive cycle.

Judgement Criteria
- When intake manifold pressure fluctuations width is lower than 2.6 kPa (0.77 in.Hg). When the EGR vacuum regulator solenoid valve is turned ON.

OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function - OBD-II Drive Cycle - Procedure 5 - Exhaust Gas Recirculation (EGR) System Monitor.

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- EGR valve does not open.
- EGR control vacuum is too low.
- EGR vacuum regulator solenoid valve failed.
- Manifold absolute pressure sensor failed.

DIAGNOSIS
Required Special Tool:
- MB991502: Scan Tool (MUT-II)

STEP 1. Check the EGR system. Refer to Emission Control System Exhaust Gas Recirculation (EGR) System - EGR System Check.

Q: Are there any abnormalities?

YES: Repair it. Then go to Step 3.
NO: Go to Step 2.

STEP 2. Using scan tool MB991502, check data list item 95: Manifold Absolute Pressure Sensor.

CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502.

1. Connect scan tool MB991502 to the data link connector.
2. Start the engine and run at idle.
3. Set scan tool MB991502 to the data reading mode for item 95, 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 18 - 32 kPa (5.3 - 11.2 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 - Procedure 5 - Exhaust Gas Recirculation (EGR) System Monitor.
2. Check the diagnostic trouble code (DTC).

Q: Is DTC P0401 set?

YES: Retry the troubleshooting.
NO: The inspection is complete.