Lexus NX: Exhaust Gas Recirculation Flow Insufficient Detected (P0401)

Lexus NX Service Manual / Engine & Hybrid System / 2ar-fxe (engine Control) / Sfi System / Exhaust Gas Recirculation Flow Insufficient Detected (P0401)

DESCRIPTION

Based on the driving conditions, the ECM regulates the volume of exhaust gas that is recirculated to the engine's combustion chambers and thus lowers the combustion temperature to reduce NOx emissions. The ECM monitors signals such as engine speed, engine coolant temperature, electric load, and vehicle speed. When the EGR permission conditions are fulfilled, the ECM controls the opening of the EGR valve linearly through signals to the EGR step motor.

DTC No.	Detection Item	DTC Detection Condition	Trouble Area	MIL	Memory
P0401	Exhaust Gas Recirculation Flow Insufficient Detected	Change in intake manifold pressure is small when the EGR valve opened and closed during fuel cut operation. (2 trip detection logic)	EGR valve assembly EGR passage EGR cooler assembly Intake system Manifold absolute pressure sensor ECM	Comes on	DTC stored

MONITOR DESCRIPTION

The ECM monitors the pressure inside the intake manifold while opening and closing the EGR valve during fuel cut operation. If there is no change in the manifold absolute pressure sensor value, the ECM interprets this as a malfunction of the EGR valve assembly, ECM will illuminate this MIL and store this DTC (2 trip detection logic).

MONITOR STRATEGY

Related DTC	P0401: EGR valve high flow rate/low flow rate
Required Sensors/Components (Main)	EGR valve assembly Manifold absolute pressure sensor
Required Sensors/Components (Related)	Engine coolant temperature sensor
Frequency of Operation	Once per driving cycle
Duration	Within 3 seconds
MIL operation	2 driving cycles
Sequence of operation	None

TYPICAL ENABLING CONDITIONS

Monitor runs whenever following DTCs are not stored	P0010 (Camshaft timing oil control valve) P0011 (VVT system - advance) P0012 (VVT system - retard) P0016 (VVT system - misalignment) P0031, P0032, P101D (Air fuel ratio sensor heater) P0102, P0103 (Mass air flow meter) P0106, P0107, P0108 (Manifold absolute pressure) P0112, P0113 (Intake Air Temperature Sensor) P0115, P0117, P0118 (Engine coolant temperature sensor) P0120, P0121, P0122, P0123, P0220, P0222, P0223, P2135 (Throttle position sensor) P0125 (Insufficient coolant temperature for closed loop fuel control) P014C, P014D, P015A, P015B, P2195, P2196, P2237, P2238, P2239, P2252, P2253 (Air fuel ratio sensor) P0171, P0172 (Fuel system) P0327, P0328 (Knock Sensor) P0335 (Crankshaft position sensor) P0340 (Camshaft position sensor) P0340, P0342, P0343 (VVT sensor) P0351, P0352, P0353, P0354 (Igniter) P106A (Canister Pressure Sensor - Manifold Pressure Sensor correlation) P219A, P219C, P219D, P219E, P219F (Air-fuel ratio imbalance)
Time after engine started	3 seconds or more
Time after engine fuel cut	2300 msec or more
Engine speed	950 to 1600 rpm
Vehicle speed	20 km/h (12.5 mph) or more
Engine coolant temperature	73°C (163°F) or higher
Auxiliary battery voltage	11 V or higher
Intake air temperature	-10°C (14°F) or higher
Atmospheric pressure	76 kPa(abs) [570 mmHg(abs)] or higher

TYPICAL MALFUNCTION THRESHOLDS

Manifold pressure change	Less than 1.75 kPa(gauge) [13 mmHg(gauge)]
At engine speed	1050 rpm

MONITOR RESULT

Refer to detailed information in Checking Monitor Status.

Click here

P0401: Exhaust Gas Recirculation / VVT / EGR FLOW INSUFFICIENCY

Monitor ID	Test ID	Scaling	Unit	Description
$31	$BD	Multiply by 0.01	kPa	Delta Manifold Absolute Pressure

CONFIRMATION DRIVING PATTERN

Connect the Techstream to the DLC3.
Turn the power switch on (IG) and turn the Techstream on.
Clear the DTCs (even if no DTCs are stored, perform the clear DTC procedure).
Turn the power switch off and wait for at least 30 seconds.
Turn the power switch on (IG) and turn the Techstream on.
Put the engine in inspection mode (maintenance mode).
Click here
Start the engine and warm it up until the engine coolant temperature reaches 73°C (163°F) or higher [A].
With the engine running, accelerate the vehicle to 75 km/h (47 mph) or more by depressing the accelerator pedal for at least 10 seconds [B].
CAUTION:

When performing the confirmation driving pattern, obey all speed limits and traffic laws.

HINT:

When accelerating the vehicle, depress the accelerator pedal more than normal to start the engine.
Idle the engine for 30 seconds or more [C].
With the engine running, accelerate the vehicle to 75 km/h (47 mph) with the shift lever in S [D].
CAUTION:

When performing the confirmation driving pattern, obey all speed limits and traffic laws.

HINT:

If the engine stops, further depress the accelerator pedal to restart the engine.
Perform the fuel cut operation for 5 seconds or more, with the accelerator pedal fully released [E].
HINT:

When the fuel cut is operating, "Idle Fuel Cut" in Data List is ON.
Enter the following menus: Powertrain / Engine and ECT / Monitor / Current Monitor [F].
Check that Exhaust Gas Recirculation/VVT / Current is Complete.
HINT:

If the monitor item Exhaust Gas Recirculation/VVT / Current is Incomplete, perform the driving pattern again.
Enter the following menus: Powertrain / Engine and ECT / Monitor / Current Monitor / Exhaust Gas Recirculation / VVT / Details.
Check the Details (EGR FLOW INSUFFICIENCY).
HINT:

Make sure that the value is between MIN and MAX.
If the monitor item Exhaust Gas Recirculation/VVT / Current is still Incomplete, perform the following procedure.
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
Read the pending DTCs.
HINT:
- If a pending DTC is output, the system is malfunctioning.
- If a pending DTC is not output, perform the following procedure.
Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
Input the DTC P0401.

Check the DTC judgment result.

Techstream Display	Description
NORMAL	DTC judgment completed System normal
ABNORMAL	DTC judgment completed System abnormal
INCOMPLETE	DTC judgment not completed Perform driving pattern after confirming DTC enabling conditions
N/A	Unable to perform DTC judgment Number of DTCs which do not fulfill DTC preconditions has reached ECU memory limit

HINT:

If the judgment result shows NORMAL, the system is normal.
If the judgment result shows ABNORMAL, the system has a malfunction.

If the judgment result is INCOMPLETE or N/A and no pending DTC is output, perform a universal trip and check for permanent DTCs.
Click here
HINT:
- If a permanent DTC is output, the system is malfunctioning.
- If no permanent DTC is output, the system is normal.

WIRING DIAGRAM

Refer to the DTC P0403.

Click here

CAUTION / NOTICE / HINT

HINT:

By using the Control the EGR Step Position Active Test, the operation of the EGR valve can be checked.
If the EGR valve is normal and is opened using the Active Test, the Data List value changes as follows.

Data List Item

Change in Data List when Number of Steps is Increased Using Control the EGR Step Position Active Test

MAP

Pressure rises
Read freeze frame data using the Techstream. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, if the engine was warmed up or not, if the air fuel ratio was lean or rich, and other data from the time the malfunction occurred.

Data List Item	Change in Data List when Number of Steps is Increased Using Control the EGR Step Position Active Test
MAP	Pressure rises

PROCEDURE

1.	CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO P0401)

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

(d) Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

(e) Read the DTCs.

Powertrain > Engine and ECT > Trouble Codes

Result	Proceed to
DTC P0401 is output	A
DTC P0401 and other DTCs are output	B

HINT:

If any DTCs other than P0401 are output, troubleshoot those DTCs first.

GO TO DTC CHART

2.	PERFORM ACTIVE TEST USING TECHSTREAM (CONTROL THE EGR STEP POSITION)

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

(d) Put the engine in inspection mode (maintenance mode).

Click here

Powertrain > Hybrid Control > Utility

Tester Display
Inspection Mode

(e) Start the engine and warm it up until the engine coolant temperature reaches 75°C (167°F) or higher.

HINT:

The A/C switch and all accessory switches should be off.

(f) Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position / Primary / MAP and Throttle Idle Position.

Powertrain > Engine and ECT > Active Test

Active Test Display
Control the EGR Step Position

Data List Display
MAP
Throttle Idle Position

(g) Confirm that the Throttle Idle Position is ON and check the MAP values in the Data List while performing the Active Test.

HINT:

Do not leave the EGR valve open for 10 seconds or more during the Active Test.
Be sure to return the EGR valve to step 0 when the Active Test is completed.
Do not open the EGR valve 30 steps or more during the Active Test.

OK:

MAP change in response to EGR step position when Throttle Idle Position is ON in Data List.

Standard:

-	EGR Step Position (Active Test)
0 Steps	0 to 30 Steps
MAP (Data List)	(EGR valve is fully closed)	MAP value is at least +10 kPa (75 mmHg) higher than when EGR valve is fully closed

EGR Step Position (Active Test)

0 Steps

0 to 30 Steps

MAP

(Data List)

(EGR valve is fully closed)

MAP value is at least +10 kPa (75 mmHg) higher than when EGR valve is fully closed

HINT:

While performing the Active Test, if the increase in the value of MAP is small, the EGR valve assembly may be a malfunctioning.
Even if the EGR valve assembly is malfunctioning, rough idling or an increase in the value of MAP may occur while performing the Active Test. However, the amount that the value of MAP increases will be smaller than normal.

GO TO STEP 4

3.	INSPECT EGR VALVE ASSEMBLY

(a) Remove the EGR valve assembly.

Click here

(b) Check for contamination between the EGR valve and housing.

OK:

EGR valve is closed and no deposits.

GO TO STEP 5

4.	REPLACE EGR VALVE ASSEMBLY

(a) Replace the EGR valve assembly.

Click here

HINT:

Perform "Inspection After Repair" after replacing the EGR valve assembly.

Click here

5.	CHECK FOR DEPOSIT (INTAKE MANIFOLD - EGR VALVE ASSEMBLY - EXHAUST MANIFOLD)

(a) Check for exhaust gas leaks at each connection point.

(b) Check for cracks, damage, and clogs in the pipes between the exhaust manifold converter sub-assembly, the intake manifold and the EGR valve assembly.

(d) Check if there is a built-up of deposits in the EGR valve of pipes.

OK:

No deposits

HINT:

Perform "Inspection After Repair" after repairing or replacing the exhaust system.

Click here

REPAIR OR REPLACE MALFUNCTIONING PARTS, COMPONENTS AND AREAS

6.	INSPECT EGR COOLER ASSEMBLY

(a) Check for blockage of the EGR cooler assembly.

OK:

No blockage.

REPLACE EGR COOLER ASSEMBLY

7.	READ VALUE USING TECHSTREAM (MAP)

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

(d) Enter the following menus: Powertrain / Engine and ECT / Data List / Primary / MAP.

Powertrain > Engine and ECT > Data List

Tester Display
MAP

(e) Read the MAP value.

Standard:

Engine condition	Techstream Display
Power switch on (IG)	80 to 110 kPa(abs) [600 to 825 mmHg(abs)]

GO TO STEP 10

8.	CHECK INTAKE SYSTEM

(a) Check the intake system for vacuum leaks.

Click here

OK:

No leaks in intake system.

HINT:

Perform "Inspection After Repair" after repairing or replacing the intake system.

Click here

REPAIR OR REPLACE INTAKE SYSTEM

9.	REPLACE MANIFOLD ABSOLUTE PRESSURE SENSOR

(a) Replace the manifold absolute pressure sensor.

Click here

10.	CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

(d) Clear the DTCs.

Powertrain > Engine and ECT > Clear DTCs

(e) Turn the power switch off and wait for at least 30 seconds.

(f) Turn the power switch on (IG).

(g) Turn the Techstream on.

(h) Drive the vehicle in accordance with the driving pattern described in Confirmation Driving Pattern.

(i) Enter the following menus: Powertrain / Engine and ECT / Trouble Codes / Pending.

(j) Read the pending DTCs.

Powertrain > Engine and ECT > Trouble Codes

HINT:

If a pending DTC is output, the system is malfunctioning.
If a pending DTC is not output, perform the following procedure.

(k) Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.

Powertrain > Engine and ECT > Utility

Tester Display
All Readiness

(l) Input the DTC: P0401.

(m) Check the DTC judgment result.

Result

Techstream Display	Description
NORMAL	DTC judgment completed System normal
ABNORMAL	DTC judgment completed System abnormal
INCOMPLETE	DTC judgment not completed Perform driving pattern after confirming DTC enabling conditions
N/A	Unable to perform DTC judgment Number of DTCs which do not fulfill DTC preconditions has reached ECU memory limit

END

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