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 <M/T> or PCM <A/T> checks how the EGR gas flow signal changes.
DESCRIPTIONS OF MONITOR METHODS
• The changes in the intake manifold pressure is monitored while the EGR valve opens and closes, and if the changes are small, the EGR flow rate is determined to be insufficient.
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
• Barometric pressure sensor
• Intake air temperature sensor
• Engine coolant temperature sensor
• Throttle position sensor
• Manifold differential 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 1,800 <M/T> or 880 and 1,800 <A/T> 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 1.5 km/h (1 mph) <M/T> or 30 km/h (19 mph) <A/T> 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 15 <M/T> or 25 <A/T> percent.
While fuel is being shut off. <M/T>
20 seconds have elapsed from the start of the previous monitoring.
The ECM <M/T> or PCM <A/T> monitors for this condition for 3 cycles of 2 seconds each during the drive cycle.

Judgement Criterion
• The intake manifold pressure fluctuation width is lower than 3.5 kPa (1 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 - Pattern 3 .
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 differential pressure sensor failed.
• ECM failed. <M/T>
• PCM failed. <A/T>