Description

DATA TROUBLE CODE: P0401

SYSTEM: Exhaust Gas Recirculation Flow Insufficient Detected

CIRCUIT DESCRIPTION





The Exhaust Gas Recirculation 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 Exhaust Gas Recirculation is regulated by the Exhaust Gas Recirculation Vacuum Modulator according to the engine load.
If even one of the following conditions is fulfilled, the Vacuum Switching Valve is turned ON by a signal from the Engine Control Module. This results in atmospheric air acting on the Exhaust Gas Recirculation Valve, closing the Exhaust Gas Recirculation Valve and shutting off the exhaust gas (Exhaust Gas Recirculation cut-off).

Under the following conditions, Exhaust Gas Recirculation is cut to maintain driveability;
- Coolant temp. below 60°C (140°F).
- During deceleration (throttle valve closed).
- Light engine load (amount of intake air very small).
- Engine racing.

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 Exhaust Gas Recirculation gas temperature sensor value does not exceed 40°C (72°F) above the ambient air temperature (2 trip detection logic).

TROUBLE AREA
- Exhaust Gas Recirculation Valve stuck closed.
- Short in Exhaust Gas Recirculation Vacuum Switching Valve circuit.
- Open in Exhaust Gas Recirculation Gas Temperature Sensor circuit.
- Exhaust Gas Recirculation hose disconnected.
- Engine Control Module.

SYSTEM CHECK DRIVING PATTERN





1. Connect the OBDII scan tool or LEXUS hand-held tester to the Data Link Connector 3.
2. Start and warm up the engine with all accessories switched OFF.
3. After the engine is warmed up, run the vehicle at 70 - 90 km/h (43 - 56 mph) for 3 minutes or more.
4. After driving, idle the engine for about 2 minutes.
5. After idling, check the "READINESS TESTS". If "COMPL" (test completed) is displayed, the system is normal. If "INCPL" is displayed, run the vehicle again and check it. If there is a malfunction in the system, "INCPL" (test incomplete) will be displayed, so perform troubleshooting.