Lexus ES300 (1997 year). Service manual - part 326

–

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 

DI–71

.

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 

DI–164

, 

DI–14

).

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 

SF–50

).

NG

 Replace VSV for EGR.

OK

Check for short in harness between VSV for
EGR and ECM.

4

Check EGR valve (See page 

EC–7

).

NG

 Repair or replace EGR valve.

OK

5

Check EGR valve position sensor (See page 

DI–118

).

NG

 Repair or replace EGR valve position sensor or
 harness.

OK

Check and replace ECM (See page 

IN–27

).

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 

DI–164

, 

DI–14

).

OK

 Go to step 4.

NG

3

Check operation of VSV for EGR (See page 

SF–50

).

NG

 Replace VSV for EGR.

OK

Check for short in harness between VSV for
EGR and ECM.

4

Check EGR valve (See page 

EC–7

).

NG

 Repair or replace EGR valve.

OK

5

Check EGR valve position sensor (See page 

DI–118

).

NG

 Repair or replace EGR valve position sensor or
 harness.

OK

Check and replace ECM (See page 

IN–27

).

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