Lexus ES300 (1997 year). Service manual — part 326
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DIAGNOSTICS
ENGINE
DI–81
233
1997 LEXUS ES300 (RM511U)
DTC
P0402
Exhaust Gas Recirculation Flow
Excessive Detected
CIRCUIT DESCRIPTION
Refer to DTC P0401 (Exhaust Gas Recirculation Flow Insufficient Detected) on page
DTC No.
DTC Detecting Condition
Trouble Area
P0402
When the EGR cut–off, the 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 for SYSTEM CHECK DRIVING PATTERN and WIRING DIAGRAM.
INSPECTION PROCEDURE
LEXUS 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
).
OK
Go to step 4.
NG
DI09T–01
DI–82
–
DIAGNOSTICS
ENGINE
234
1997 LEXUS ES300 (RM511U)
3
Check operation of VSV for EGR (See page
NG
Replace VSV for EGR.
OK
Check for short in harness between VSV for
EGR and ECM.
4
Check EGR valve (See page
NG
Repair or replace EGR valve.
OK
5
Check EGR valve position sensor (See page
).
NG
Repair or replace EGR valve position sensor or
harness.
OK
Check and replace ECM (See page
).
OBDII scan tool (excluding LEXUS hand–held tester)
1
Check connection and blockage of vacuum hose.
NG
Repair or replace vacuum hose.
OK
–
DIAGNOSTICS
ENGINE
DI–83
235
1997 LEXUS ES300 (RM511U)
2
Check VSV for EGR (See page
).
OK
Go to step 4.
NG
3
Check operation of VSV for EGR (See page
NG
Replace VSV for EGR.
OK
Check for short in harness between VSV for
EGR and ECM.
4
Check EGR valve (See page
NG
Repair or replace EGR valve.
OK
5
Check EGR valve position sensor (See page
).
NG
Repair or replace EGR valve position sensor or
harness.
OK
Check and replace ECM (See page
).
FI7081
Waveform of Oxygen Sensor
before Catalyst
Normal Catalyst
Waveform of Oxygen Sensor
after Catalyst
FI7132
Engine Speed
2,500
∼
3,000 rpm
Idling
IG SW OFF
(1)
(2)
(3)
(4)
Time
Warmed up
3 min. or so
Check
DI–84
–
DIAGNOSTICS
ENGINE
236
1997 LEXUS ES300 (RM511U)
DTC
P0420
Catalyst System Efficiency Below Threshold
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 Condition
Trouble Area
P0420
After the engine and the catalyst are warmed up, and while
the vehicle is driven within the set vehicle and engine speed
range, the waveforms of the heated oxygen sensors (bank 1, 2
sensor 1 and bank 1 sensor 2) have the same amplitude
(2 trip detection logic)
Three–way catalytic converter
Open or short in heated oxygen
sensor
(bank 1, 2 sensor 1/ bank 1 sensor 2) circuit
Heated oxygen sensor (bank 1, 2 sensor 1/ bank 1 sensor 2)
HINT:U.S.A. and Canadian vehicles does the MIL light up when a malfunction is detected.
CONFIRMATION ENGINE RACING PATTERN
DI09U–01
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