P0401

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 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 the accessories switched OFF.
3. Run the vehicle at 70 - 90 kph (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.
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 steps (2) to (6) from some times 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 light up after step (7) above is done. (2trip detection logic)

INSPECTION PROCEDURE

HINT: 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 was warmed up or not, the air-fuel ratio was lean or rich, etc. at the time of the malfunction.