Page 2721 of 4770
S05410
Vacuum
EGR Valve
± DIAGNOSTICSENGINE (1MZ±FE)
DI±301
536 Author: Date:
7 Check EGR valve.
PREPARATION:
(a) Disconnect the vacuum hose from EGR valve.
(b) Start the engine.
CHECK:
Check whether the engine stall when apply vacuum to EGR
valve.
OK:
Engine runs rough or stall.
NG Repair or replace EGR valve.
OK
8 Check vacuum control valve (See page EC±11).
NG Replace vacuum control valve.
OK
Check and replace ECM (See page IN±31).
Page 2722 of 4770

DI±302
± DIAGNOSTICSENGINE (1MZ±FE)
537 Author: Date:
DTC P0402 Exhaust Gas Recirculation Flow
Excessive Detected (Ex CA Spec.)
CIRCUIT DESCRIPTION
Refer to DTC P0401 (Exhaust Gas Recirculation Flow Insufficient Detected) on page DI±292.
DTC No.DTC Detecting ConditionTrouble Area
P0402
When EGR cut±off, lift amount of EGR valve is
2.6 mm (0.1 in.) or more
(2 trip detection logic)
EGR valve stuck open
VSV for EGR open malfunction
Short in VSV circuit for EGR
Open or short in EGR valve position sensor circuit
EGR valve position sensor
ECM
See DTC P0401 (Exhaust Gas Recirculation Flow Insufficient Detected) on See page DI±292 for SYS-
TEM CHECK DRIVING PATTERN and WIRING DIAGRAM.
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 warmed up or not, the air±fuel ratio lean or rich, etc.
at the time of the malfunction.
TOYOTA hand±held tester
1 Check connection and blockage of vacuum hose.
NG Repair or replace vacuum hose.
OK
2 Check VSV for EGR (See page DI±292, step 5).
OK Go to step 4.
NG
DI07X±06
Page 2723 of 4770
± DIAGNOSTICSENGINE (1MZ±FE)
DI±303
538 Author: Date:
3 Check operation of VSV for EGR (See page SF±56).
NG Replace VSV for EGR.
OK
Check for short in harness between VSV for
EGR and ECM (See page IN±31).
4 Check EGR valve (See page EC±11).
NG Repair or replace EGR valve.
OK
5 Check EGR valve position sensor (See page DI±358).
NG Repair or replace EGR valve position sensor or
harness.
OK
Check and replace ECM (See page IN±31).
OBDII scan tool (excluding TOYOTA hand±held tester)
1 Check connection and blockage of vacuum hose.
NG Repair or replace vacuum hose.
OK
Page 2724 of 4770
DI±304
± DIAGNOSTICSENGINE (1MZ±FE)
539 Author: Date:
2 Check VSV for EGR (See page DI±292, step 5).
OK Go to step 4.
NG
3 Check operation of VSV for EGR (See page SF±56).
NG Replace VSV for EGR.
OK
Check for short in harness between VSV for
EGR and ECM (See page IN±31).
4 Check EGR valve (See page EC±11).
NG Repair or replace EGR valve.
OK
5 Check EGR valve position sensor (See page DI±358).
NG Repair or replace EGR valve position sensor or
harness.
OK
Check and replace ECM (See page IN±31).
Page 2725 of 4770

FI7081
Waveform of Oxygen Sensor
before CatalystNormal Catalyst Waveform of Oxygen Sensor
after Catalyst
FI7132
Engine Speed
2,500 ~ 3,000 rpm
Idling
IG SW OFF(a)(b)(c) (d)
Time Warmed up 3 min. or so Check
± DIAGNOSTICSENGINE (1MZ±FE)
DI±305
540 Author: Date:
DTC P0420 Catalyst System Efficiency Below Threshold
(Except California Spec.)
CIRCUIT DESCRIPTION
The ECM compares the waveform of the oxygen sensor located before the catalyst with the waveform of
the oxygen sensor located after the catalyst to determine whether or not catalyst performance has deterio-
rated.
Air±fuel ratio feedback compensation keeps the waveform of the oxygen sensor before the catalyst repeat-
edly changing back and forth from rich to lean.
If the catalyst is functioning normally, the waveform of the oxygen sensor after the catalyst switches back
and forth between rich and lean much more slowly than the waveform of the oxygen sensor before the cata-
lyst.
But when both waveforms change at a similar rate, it indicates that catalyst performance has deteriorated.
DTC No.DTC Detecting ConditionTrouble Area
P0420
After engine and catalyst are warmed up, and while vehicle is
driven within set vehicle and engine speed range, waveforms
of heated oxygen sensors (bank 1 sensor 1, 2) have the same
amplitude
(2 trip detection logic)
Three±way catalytic converter
Open or short in heated oxygen sensor circuit
Heated oxygen sensor
CONFIRMATION ENGINE RACING PATTERN
DI07Y±06
Page 2726 of 4770

FI6514
OX Signal Waveform (Oscilloscope)
1 V
0 V
200 m sec./Division
DI±306
± DIAGNOSTICSENGINE (1MZ±FE)
541 Author: Date:
(a) Connect the TOYOTA hand±held tester to the DLC3, or connect the probe of the oscilloscope between
terminals OXR1, OXL1, OXS and E1 of the ECM connector.
(b) Start engine and warm it up with all accessories switched OFF until water temp. is stable.
(c) Race the engine at 2,500 ~ 3,000 rpm for about 3 min.
(d) After confirming that the waveform of the heated oxygen sensor, bank 1, 2 sensor 1 (OXR1, OXL1),
oscillate around 0.5 V during feedback to the ECM, check the waveform of the heated oxygen sensor,
bank 1 sensor 2 (OXS).
HINT:
If there is a malfunction in the system, the waveform of the
heated oxygen sensor, bank 1 sensor 2 (OXS), is almost the
same as that of the heated oxygen sensor, bank 1, 2 sensor 1
(OXR1, OXL1), on the left.
There are some cases where, even though a malfunction
exists, the MIL may either light up or not light up.
INSPECTION PROCEDURE
HINT:
Read freeze frame data using TOYOTA hand±held theater or OBD II scan tool. Because freeze frame re-
cords the engine conditions when the malfunction is detected, when troubleshooting it is useful for determin-
ing whether the vehicle was running or stopped, the engine warmed up or not, the air±fuel ratio lean or rich,
etc. at the time of the malfunction.
1 Are there any other codes (besides DTC P0420) being output?
YES Go to relevant DTC chart.
NO
2 Check gas leakage on exhaust system.
NG Repair or replace.
OK
Page 2727 of 4770
± DIAGNOSTICSENGINE (1MZ±FE)
DI±307
542 Author: Date:
3 Check heated oxygen sensor (bank 1, sensor 1) (See page DI±255).
NG Repair or replace.
OK
4 Check heated oxygen sensors (bank 1, 2 sensor 2) (See page DI±265).
NG Repair or replace.
OK
Replace three±way catalytic converter.
Page 2728 of 4770

A01674
Waveform of
A/F Sensor
Normal CatalystWaveform of Heated Oxygen
Sensor Behind Catalyst
Abnormal Catalyst DI±308
± DIAGNOSTICSENGINE (1MZ±FE)
543 Author: Date:
DTC P0420 Catalyst System Efficiency Below Threshold
(Only for California Spec.)
CIRCUIT DESCRIPTION
The ECM observes the waveform of the heated oxygen sensor located behind the catalyst to determine
whether the catalyst is performance has deteriorated.
If the catalyst is functioning normally, the waveform of the heated oxygen sensor located behind the catalyst
switches back and forth between rich and lean much more slowly.
When the waveform of the heated oxygen sensor located behind the catalyst alternates flatteringly between
rich and lean, it indicates that catalyst performance has deteriorated.
DTC No.DTC Detecting ConditionTrouble Area
P0420
After engine and catalyst are warmed up, and while vehicle is
driven within set vehicle and engine speed range, waveform of
heated oxygen sensor (bank 1 sensor 2) alternates flatteringly
between rich and lean
(2 trip detection logic)Three±way catalytic converter
Open or short in heated oxygen sensor
(bank 1 sensor 2) circuit
Heated oxygen sensor (bank 1 sensor 2)
Open or short in A/F sensors (bank 1, 2 sensor 1) circuit
A/F sensors (bank 1, 2 sensor 1)
DI1K4±03