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 lift amount of EGR valve is controlled by the vacuum which is regulated by the Duty-VSV operated by the ECM. The lift amount of EGR valve is detected by the EGR valve position sensor which is mounted on the EGR valve and it provides feedback to the ECM to control the lift amount of EGR valve in response to engine operating conditions.
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 speed over 4,000 rpm
- Engine idling

DETECTING CONDITION

WIRING DIAGRAM

SYSTEM CHECK DRIVING PATTERN
(a) Connect the OBD II scan tool or LEXUS hand-held tester to the DLC3.
(b) Start and warm up the engine with all accessories switched OFF.
(c) Run the vehicle at 70 - 90 km/h (43 - 56 mph) for 3 min. or more.
(d) Idle the engine for about 2 min.
(e) Start the engine and do steps (c) and (d) again.
(f) Check the READINESS TESTS mode on the OBD II scan tool or LEXUS 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 step
(e) for some times and check it.

HINT: INCMPL is displayed when either condition (1) or (2) exists.

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

INSPECTION PROCEDURE

HINT: Read freeze frame data using LEXUS 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.