P0401

CIRCUIT DESCRIPTION

DTC Detection Condition:

The EGR system recirculates exhaust gas, which is controlled to the proper quantity to suit the driving conditions, into the intake air mixture so as to slow down the 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 the atmospheric air acting on the EGR valve, closing the EGR valve and shutting oft the exhaust gas (EGR cut-off).

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

Wiring Diagram:

SYSTEM CHECK DRIVING PATTERN
a. Connect the OBD II scan tool or TOYOTA hand-held tester to the DLC3.
b. Start and warm up the engine with all the accessories switched OFF.
c. Run the vehicle at 60 - 80 km/h (38 - 50 mph) for 3 minutes or more.
d. Idle the engine for about 2 minutes.
e. Do steps (c) and (d) again.
f. Stop in a safe place and turn the ignition switch OFF.
g. Do steps b.to e.again.
h. 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 (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 will light up after steps b.to e.above are done (2 trip detection logic).

Step 1:

Steps 2 - 4:

Steps 5 - 7:

INSPECTION PROCEDURE

HINT:
- If DTCs P0105, P0106 and P0401 are output simultaneously, perform a troubleshooting of DTC P0105 first.
- If DTCs P0401 and P0402 are output simultaneously, perform troubleshooting of DTC P0402 first.
- Read freeze frame data using TOYOTA hand-held tester or OBD II scan tool, as freeze frame data records the engine conditions when a 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.

Step 1:

Steps 2 - 4:

Steps 4 (continued) - 7:

OBD II scan tool (excluding TOYOTA hand-held tester):