P0401

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 valve1 closing the EGR valve and shutting off the exhaust gas (EGR cut-off).
Under the following conditions, EGR is cut to maintain driveability.
- Before the engine is warmed up.
- During deceleration (throttle valve closed).
- Light engine load (amount of intake air very small).
- Engine idling.
- Engine speed over 4,400 rpm.
- High engine load (amount of intake air very large).

DETECTING CONDITIONS

WIRING DIAGRAM

SYSTEM CHECK DRIVING PATTERN
(1) Connect the OBD II scan tool or TOYOTA hand-held tester to the DLC3.
(2) Start and warm up the engine with all accessories switched OFF.
(3) Run the vehicle at 70 - 90 km/h (43 - 56 mph) for 3 min. or more.
(4) Idle the engine for about 2 min.
(5) Do steps (3) and (4) again.
(6) Stop at safe place and turn the ignition switch OFF.
(7) Do step (2) to (5) again. hand-held tester.
(8) Check the READINESS TESTS mode on the OBD II scan tool or TOYOTA hand-held tester.
If COMPL is displayed and the MIL does not light up, the system is normal.
If INCMPL is displayed and the MIL does not light up, run the vehicle again and check it.

HINT: INCMPL is displayed when either condition (a) or (b) exists.

(a) The system check is incomplete.
(b) There is a malfunction in the system.
If there is a malfunction in the system, the MIL will light up after steps (b) to (f) above are done. (2 trip detection logic)

INSPECTION PROCEDURE

HINT:
- If DTC P0105 (Manifold Absolute Pressure/Barometric Pressure Circuit Malfunction) and/or P0106 (Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance Problem) and P0401 (Exhaust Gas Recirculation Flow Insufficient Detected) are output simultaneously, perform trouble- shooting of DTC P0105 first.
- If DTC P0401 (Exhaust Gas Recirculation Flow Insufficient Detected) and P0402 (Exhaust Gas Recirculation Flow Excessive Detected) are output simultaneously, perform troubleshooting of DTC P0402 first.
- Read freeze frame data using TOYOTA hand-held tester or OBD II scan tool. Because freeze frame records the engine conditions when the malfunction is detected, when troubleshooting it is useful for determining whether the vehicle was running or stopped, the engine warmed up or not, the air-fuel ratio lean or rich, etc. at the time of the malfunction.

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TOYOTA hand-held tester: