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 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 910 and 1,650 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 30 km/h (18.7 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 28 percent.
• The 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 2.0 kPa (0.59 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.
• Open or shorted EGR vacuum regulator solenoid valve circuit, or connector damage.
• Manifold absolute pressure sensor failed.
• PCM failed.