Toyota 1 MZ–FE Manual page 512

EG2–512
DTC P0401 Exhaust Gas Recirculation Flow
Insufficient Detected
CIRCUIT DESCRIPTION
The EGR system recirculates exhaust gas, which is controlled to the proper quantity to suit the driving
conditions, into the intake air mixture to slow down combustion, reduce the combustion temperature and
reduce NOx emissions. The amount of EGR is regulated by the EGR vacuum modulator according to the
engine load.
If even one of the following conditions is fulfilled,
the VSV is turned ON by a signal from the ECM.
This results in atmospheric air acting on the EGR
valve, closing the EGR valve and shutting off the
exhaust gas (EGR cut–off).
Under the following conditions, EGR is cut to
maintain driveability.
Coolant temp. below 602C (1402F).
During deceleration (throttle valve closed).
Light engine load (amount of intake air very
small).
Engine racing.
DTC No. Diagnostic Trouble Code Detecting Condition
After the engine is warmed up and run at 80 km/h
(50 mph) for 3 to 5 minutes, the EGR gas
temperature sensor value does not exceed 402C
P0401
(1042F) above the ambient air temperature.
(2 trip detection logic)
1MZ–FE ENGINE – CIRCUIT INSPECTION
EGR valve stuck closed.
Short in EGR VSV circuit.
Open in EGR gas temp. sensor circuit.
EGR hose disconnected.
ECM
Trouble Area