Toyota TechDoc

DTC P0401 Exhaust Gas Recirculation Flow Insufficient Detected

for Preparation Click here

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, 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.
The ECM opens and closes the EGR valve during fuel-cut and monitors changes in the manifold absolute pressure to detect poor movement or sticking of the EGR valve.

DTC No.	DTC Detection Condition	Trouble Area
P0401	Target and actual manifold absolute pressure rates differ (2-trip detection logic)	Open or short in EGR circuit EGR valve assembly EGR passage Manifold absolute pressure sensor ECM

HINT:

DTC P0401 is set while the engine is in fuel cut condition and the brake pedal is pressed for 5 seconds.
If DTC P0403 has already been set, P0401 is not set.

WIRING DIAGRAM

INSPECTION PROCEDURE

NOTICE:

Inspect the fuses for circuits related to this system before performing the following inspection procedure.

HINT:

Read freeze frame data using an intelligent tester. 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.

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

Connect the intelligent tester to the DLC3.

Turn the ignition switch to ON.

Turn the tester on.

Enter the following menus: Powertrain / Engine and ECT / DTC.

Read the DTC.

Result
Result	Proceed to
P0401	A
P0401 and P0403	B

CHECK EGR VALVE CIRCUIT (Click here)

A

2.PERFORM ACTIVE TEST USING INTELLIGENT TESTER (OPERATE EGR VALVE)

Connect the intelligent tester to the DLC3.

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.

Turn the tester on.

Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position.

Check the MAP in Data List and the idling condition while performing Active Test.
OK:
MAP and idling condition change in response to EGR step position.

Standard:

-	EGR Step Position (Active Test)
-	0 Steps	0 to 30 Steps	30 to 40 Steps or Higher
Idling condition	Steady idling	Engine changes from steady to rough idling	Engine changes from rough idling to engine stall
MAP value (Data List)	28 to 48 kPa (EGR valve is fully closed)	MAP value is at least +10 to 15 kPa higher than when EGR valve is fully closed	80 to 110 kPa (After engine stall)

HINT:

During Active Test, if the idling condition does not change in response to EGR step position, then there is probably a malfunction in EGR valve.

EGR Valve is Sticking in Close Side:

-	EGR Step Position (Active Test)
-	0 Steps	30 Steps or Higher
Idling condition	Steady idling	Steady idling

EGR Valve is Sticking in Open Side
-	EGR Step Position (Active Test)
-	0 Steps	30 Steps or Higher
Idling condition	Rough idling or engine stall (Engine difficult to start)	Rough idling or engine stall (Engine difficult to start)

Result
Result	Proceed to
Outside standard range	A
Within standard range	B

Go to step 9

A

3.READ VALUE USING INTELLIGENT TESTER (MANIFOLD ABSOLUTE PRESSURE SENSOR)

Connect the intelligent tester to the DLC3.

Warm up the engine.

Turn the tester on.

Enter the following menus: Powertrain / Engine and ECT / Data List / MAP.

Read the MAP value at racing the engine.
Standard:
Engine condition
Tester Display
Ignition switch ON
80 to 110 kPa
racing the engine
Changes in response to accelerator pedal operation

Go to step 8

OK

4.CHECK FOR DEPOSIT (EXHAUST MANIFOLD CONVERTER TO EGR VALVE ASSEMBLY)

Check for cracks, damage, and clogs in the pipes between the exhaust manifold converter and the EGR valve assembly.

Check for exhaust leaks at each connection point.

HINT:

This check may require the removal of components (Click here).

OK:: No deposit

REPAIR OR REPLACE MALFUNCTIONING PARTS, COMPONENT AND AREA

OK

5.CHECK FOR DEPOSIT (EGR VALVE ASSEMBLY TO INTAKE PORT)

Check for cracks, damage, and clogs in the pipes between the exhaust manifold converter and the EGR valve assembly.

Check for exhaust leaks at each connection point.

HINT:

This check may require the removal of components (Click here).

OK:: No deposit

REPAIR OR REPLACE MALFUNCTIONING PARTS, COMPONENT AND AREA

OK

6.REPLACE EGR VALVE ASSEMBLY

Replace the EGR valve assembly (Click here).

NEXT

7.CHECK WHETHER DTC OUTPUT RECURS (DTC P0401)

Connect the intelligent tester to the DLC3.

Turn the ignition switch to ON.

Turn the tester on.

Clear the DTC.

Turn the ignition switch off and wait for 30 seconds.

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.

Switch the ECM from normal mode to check mode.

Drive the vehicle at 60 km/h (37 mph) with the shift lever in B (2nd or 3rd).
CAUTION:
1. Strictly observe speed limits and traffic laws when performing the confirmation drive pattern.

Perform fuel-cut operation for 5 seconds or more, with the accelerator pedal fully released.
HINT:
1. If the deceleration was not completed, perform the confirmation driving pattern again.

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

Input the DTCs to be confirmed.

Check the DTC judgment result.

Result
Result	Proceed to
NORMAL	A
ABNORMAL	B

Intelligent Tester
Tester Display	Description
NORMAL	DTC judgment completed System normal
ABNORMAL	DTC judgment completed System abnormal
INCOMPLETE	DTC judgment not completed You should perform driving pattern after confirming DTC enabling conditions
UNKNOWN	Unable to perform DTC judgment Number of DTCs which do not fulfill DTC preconditions has reached ECU's memory limit

HINT:

If the DTC judgment result is INCOMPLETE or UNKNOWN, drive the vehicle again at 60 km/h (37 mph) with the shift lever in B (2nd or 3rd), perform fuel-cut operation for 5 seconds or more with the accelerator pedal fully released, and check the DTC judgment result.

REPLACE ECM (Click here)

END

8.INSPECT VACUUM HOSE SUB-ASSEMBLY

Vacuum hose is connected correctly and is not damaged.

If a hose is damaged do not repair by cutting, and replace with a new part.

REPLACE VACUUM HOSE SUB-ASSEMBLY

REPLACE MANIFOLD ABSOLUTE PRESSURE SENSOR (Click here)

9.CHECK HARNESS AND CONNECTOR (ECM - EGR VALVE ASSEMBLY - INTEGRATION RELAY)

Disconnect the EGR valve assembly connector.

Disconnect the ECM connector.

Remove the integration relay from engine room relay block.

Measure the resistance according to the value(s) in the table below.

Standard Resistance (Check for Open):

Tester Connection	Condition	Specified Condition
B8-51 (EGR1) - B49-4 (EGR1)	Always	Below 1 Ω
B8-50 (EGR2) - B49-3 (EGR2)	Always	Below 1 Ω
B8-49 (EGR3) - B49-6 (EGR3)	Always	Below 1 Ω
B8-48 (EGR4) - B49-1 (EGR4)	Always	Below 1 Ω
1F-10 - B49-2 (+B1)	Always	Below 1 Ω
1F-11 - B49-5 (+B2)	Always	Below 1 Ω

Standard Resistance (Check for Short):

Tester Connection	Condition	Specified Condition
B8-51 (EGR1) or B49-4 (EGR1) - Body ground	Always	10 kΩ or higher
B8-50 (EGR2) or B49-3 (EGR2) - Body ground	Always	10 kΩ or higher
B8-49 (EGR3) or B49-6 (EGR3) - Body ground	Always	10 kΩ or higher
B8-48 (EGR4) or B49-1 (EGR4) - Body ground	Always	10 kΩ or higher
1F-10 or B49-2(+B1) - Body ground	Always	10 kΩ or higher
1F-11 or B49-5(+B2) - Body ground	Always	10 kΩ or higher

Text in Illustration
*1	Front view of wire harness connector: (to EGR Valve Assembly)
*2	Front view of wire harness connector: (to ECM)
*3	Front view of wire harness connector: (to Integration Relay)

Reconnect the EGR valve assembly connector.

Reconnect the ECM connector.

Reinstall the integration relay.

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

10.READ DTC OUTPUT RECURS (DTC P0401)

Connect the intelligent tester to the DLC3.

Turn the ignition switch to ON.

Turn the tester on.

Clear the DTC.

Turn the ignition switch off and wait for 30 seconds.

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.

Switch the ECM from normal mode to check mode.

Drive the vehicle at 60 km/h (37 mph) with the shift lever in B (2nd or 3rd).
CAUTION:
1. Strictly observe speed limits and traffic laws when performing the confirmation drive pattern.

Perform fuel-cut operation for 5 seconds or more, with the accelerator pedal fully released.
HINT:
1. If the deceleration was not completed, perform the confirmation driving pattern again.

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

Input the DTCs to be confirmed.

Check the DTC judgment result.

Result
Result	Proceed to
ABNORMAL	A
NORMAL	B

Intelligent Tester
Tester Display	Description
NORMAL	DTC judgment completed System normal
ABNORMAL	DTC judgment completed System abnormal
INCOMPLETE	DTC judgment not completed You should perform driving pattern after confirming DTC enabling conditions
UNKNOWN	Unable to perform DTC judgment Number of DTCs which do not fulfill DTC preconditions has reached ECU's memory limit

HINT:

If the DTC judgment result is INCOMPLETE or UNKNOWN, drive the vehicle again at 60 km/h (37 mph) with the shift lever in B (2nd or 3rd), perform fuel-cut operation for 5 seconds or more with the accelerator pedal fully released, and check the DTC judgment result.

END

A

11.REPLACE EGR VALVE ASSEMBLY

NEXT

12.READ DTC OUTPUT RECURS (DTC P0401)

Connect the intelligent tester to the DLC3.

Turn the ignition switch to ON.

Turn the tester on.

Clear the DTC.

Turn the ignition switch off and wait for 30 seconds.

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.

Switch the ECM from normal mode to check mode.

Drive the vehicle at 60 km/h (37 mph) with the shift lever in B (2nd or 3rd).
CAUTION:
1. Strictly observe speed limits and traffic laws when performing the confirmation drive pattern.

Perform fuel-cut operation for 5 seconds or more, with the accelerator pedal fully released.
HINT:
1. If the deceleration was not completed, perform the confirmation driving pattern again.

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

Input the DTCs to be confirmed.

Check the DTC judgment result.

Result
Result	Proceed to
ABNORMAL	A
NORMAL	B

Intelligent Tester
Tester Display	Description
NORMAL	DTC judgment completed System normal
ABNORMAL	DTC judgment completed System abnormal
INCOMPLETE	DTC judgment not completed You should perform driving pattern after confirming DTC enabling conditions
UNKNOWN	Unable to perform DTC judgment Number of DTCs which do not fulfill DTC preconditions has reached ECU's memory limit

HINT:

If the DTC judgment result is INCOMPLETE or UNKNOWN, drive the vehicle again at 60 km/h (37 mph) with the shift lever in B (2nd or 3rd), perform fuel-cut operation for 5 seconds or more with the accelerator pedal fully released, and check the DTC judgment result.

END

REPLACE ECM

Engine condition	Tester Display
Ignition switch ON	80 to 110 kPa
racing the engine	Changes in response to accelerator pedal operation