Lexus SC300 / Lexus SC400. Service manual - part 935

WIRING DIAGRAM

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–107

NG

OK

OK

NG

OK

NG

INSPECTION PROCEDURE

1

Check voltage between terminal EGR of ECM connector and body ground.

C

OK

P

1.

Connect the Check Harness A. (See page 

TR–34

).

2.

Warm up engine to normal operating temperature.

Measure voltage between terminal EGR of engine (&
ECT) ECU connector and body ground.

Voltage:

Go to step 

.

2

Check resistance between terminals of VSV for EGR.

C

OK

P

Remove VSV for EGR. (See page 

EC–13

).

Measure resistance between terminals of VSV for EGR.

Resistance:

38.5 – 44.5 

 at 20



 C (68



 F)

Replace VSV for EGR.

3

Check for open and short in harness and connector between EFI main relay and VSV for EGR,

VSV for EGR and engine (& ECT) ECU. (See page 

IN–27

)

Repair or replace harness or connector.

Check and replace engine (& ECT) ECU.

TR–108

–

ENGINE TROUBLESHOOTING

Circuit Inspection

OK

NG

OK

NG

OK

NG

4

Check EGR system (See page 

EC–12

).

Repair EGR system.

5

Check resistance of EGR gas temp. sensor.

C

OK

P

Remove EGR gas temp. sensor.

Measure resistance between terminals of EGR gas
temp. sensor connector.

Resistance:

69 – 89 k

 at 50



C (122



F)

12 – 15 k

 at 100



C (212



F)

2 – 4 k

 at 150



C (302



F)

Replace EGR gas temp. sensor.

6

Check for open in harness and connector between EGR gas temp. sensor and engine (& ECT)

ECU. (See page 

IN–27

).

Repair or replace harness or connector.

Check and replace engine (& ECT) ECU.

–

ENGINE TROUBLESHOOTING

Circuit Inspection

TR–109

Diag. Code  71

EGR System Malfunction (Only for USA
spec.)

CIRCUIT DESCRIPTION

The EGR system recirculates exhaust gas, which is controlled to the proper quantity to suit the driving condi-
tions, into the intake air mixture to slow down combustion, reduce the combustion temperature and reduce NOx
emissions.
The lift amount of the EGR valve is controlled by a step motor operated by the ECU. The ECU operates the motor
only a preprogrammed amount in response to the engine operating conditions (engine rpm, intake air volume
to adjust the EGR volume to the target valve.)
Under the following conditions, EGR is cut to maintain driveability.

•

Coolant temp. below 535C (127.45F)

•

During deceleration (throttle valve
closed)

•

Light engine load (amount of intake air
very small)

•

Engine speed over 4,000 rpm

•

Engine idling

•

Neutral start switch on

Code No.

Diagnostic Code Detecting Condition

Trouble Area

(1) Open or short in EGR step motor circuit for 1 sec.

or more.

Open or short in EGR step motor circuit

ECU

71

(2)  EGR gas temp. is 65

°

C (149

°

F) or below for 

1 ~ 4 min. under conditions (a) and(b).

(2 trip detection logic)*

(a) Coolant temp.: 65

°

C (149

°

F) or more.

(b) EGR operation possible (EX. ECT in 3rd speed,

A/C ON, 60 mph (96 km/h), Flat road).

Open in EGR gas temp. sensor circuit

ECU

*: See page 

TR–21

.

TR–108

–

ENGINE TROUBLESHOOTING